hi guys welcome to my IDC se headaches our all-in-one physics video for the new specification 9 to 1 I'm so excited that it is here now these are my incredibly detailed videos where I try my absolute best to hit every single specification point as we go through you'll notice my path for answers popping up these are the exact phrases I think you should be using in the exam don't forget you can purchase my perfect answer revision guide on my website which is www.hyken.com now we're going to take a look at the speed distance time topic so there are some very key equations that you need to be aware of so you know me I love formula triangles so I'm going to have my first one here which is D at the top then ask then T now you cover whatever it is that you're after so I'm after distance so if I cover that over with my thumb I can see that it's there for speed times time if I'm after speed then we're going to do distance divided by time and then lastly time is distance divided by speed so if they ask you for the equation sure use your formula triangles to actually work out what the equation is but you must write out the full equation to get the mark formula triangles do not count so as you can see on the left hand side I've drawn very poorly a distance time graph and I'm after this speed at point a so to work out the speed I know that I need to do distance divided by time I can read that straight off the graph so I can see that the distance traveled is 8 the times was 4 seconds so simple calculations the speed is therefore 2 meters a second meters per second due to the units we can see on the y-axis which was that distance was given in meters and time was given in seconds it's important to understand these grasp fully because they could ask you for example how long was the car stationary for so in terms of stationary you're looking at the flat parts of the graph so the car is stationary here why because it remains that 8 metres throughout that time so how long was the car stationary for have a look along here and the answer here is 4 seconds this is a different type of graph so the velocity time graph or the speed time graph not to be confused with the distance time graph so we are being asked to find out the acceleration at Point a on the graph so acceleration is given by the equation acceleration in each Clause final speed minus initial speed over time and I need to wait like that is a equals b minus u over t so looking at portion a of the graph what is the final speed well it's given here so read across and you'll see that it is five the initial speed is given here and we know that's zero so five minus zero the time taken was four seconds so the answer here is one point two five now be careful your units you're looking for meters per second squared for acceleration another thing they like to ask you is to calculate the distance traveled now this is a longer task and remember distance traveled is given by the area under the graph so let's calculate the entire distance traveled by this particular vehicle so the way I like to do this is by splitting it up you can work it out as a trapezium or you can work it out as two triangles and a rectangle which I personally find easier so I'm going to label them a B and C so area a is given by this formula well it's a triangle so I need to put in a half immediately times it by the height of the triangle which is five times it by its width do the calculation and that will therefore be ten meters area B is more straightforward it's just a rectangle so just make sure you're reading the correct lengths so it's five again this time times it by three you get a value which is 15 meters finally area C we're back to our triangle so we need 1/2 times the height of the triangle which is 5 times the width of the triangle which is 2 so we get 5 meters if you add that up you get a total area of 30 meters and that therefore is the distance traveled 9.6 by measuring the length of the skid marks in an accident to investigator determines at the distance a car traveled between the brakes being applied in stopping was 22 meters the investigator used a sled to determine the friction the investigator then calculated that the car decelerated at 7.2 meters per second squared calculate the speed of a car just before the brakes were applied give your answer to two sig fig okay so this is soo bad so we're using this equation which is V squared equals u squared plus two a s and now it's just a matter of identifying what everything is so the distance here is as the acceleration is well as minus seven point two but that's the acceleration so that's a looking at the speed of the car just before the brakes were applied so we're looking for the initial speed which is U so that's the question mark and we know that it stopped so that means the final speed was zero so just substitute in all these values so it's literally zero squared which is zero equals u squared plus two times minus seven point two times the distance which was 22 so zero equals u squared minus three hundred and sixteen point eight how do we get u square bites off well add it to both sides three hundred and sixteen point eight equals u squared and then square root that answer in order to calculate your U so u will equal 18 to two significant figures I've picked up some questions so question one a toy car whilst on a ramp and hits a cushion the graph shows how its velocity changes with time so this is effectively a speed time graph constant velocity on the graph is shown by what does the word constant mean well it means same so where on this graph is it the same velocity now you can kind of imagine a y-axis and the numbers going up the y-axis so it could be something like 0 10 20 30 on the velocity front so where does that not change but it's obviously going to be the horizontal portion of the line because at that point the speed or the velocity is going to be the same everywhere so the answer here is be the horizontal parts of the line and with these sorts of questions rather than reading the options through and getting confused I would look at the question first of all work out what you think is the answer and then see if that is an option below the distance traveled is shown by well again I told you to work our distance it's the area under the graph line let's look at the options and that's a the average velocity of the toy car is given by so remember your equation velocity or speed equals distance divided by time therefore that is be a bus travels along a straight road the graph shows how the velocity of the bus changes during a short journey okay so we've got a velocity time graph so again distance will be given by area under the curve acceleration will be given by the gradient any way state the velocity of the bus after 25 seconds so you're looking up here the answer here is 6 meters per second how long is the bus stationary during its journey now I've seen loads of people get this wrong because they think that it's stationary here and here well no that's absolute rubbish because look at the velocity it's 12 so stationary means that it was standing still so standing still means that the velocity must have been zero which is just this chunk here and therefore your answer here is 10 seconds state the equation linking acceleration changing velocity and time taken they're giving you the exact wording so you want to write it out as they've written it so you're going to write acceleration equals change in velocity over time taken or you could have written a equals v minus u over T calculate the acceleration of the bus during the first 10 sec give the unit that's worth three marks so we'll have a look back up here and we're looking at this portion of the graph the first ten seconds were looking at the gradient so that equation was acceleration equals V minus u over T so that is final speed which is 12 minus initial speed which was zero over time taken which was ten so 12 taken zero over ten is one point two the units of acceleration are meters per second squared state the equation linking average speed distance meter and time taken average speed equals distance move divided by time taken the bus moves a total distance of 390 meters during the journey calculate the average speed of the bus so speed equals distance divided by time distance is 390 divided by look on the graph for whatever the time was and it was 60 seconds pop that into your calculator and your answer will be six point five meters per second the bus travels further in the first 30 seconds of its journey than it does during the last 30 seconds of this journey explain how the graph shows this well remember that I told you distance is given area by area under the graph line and you can see that the trapezium for the first 30 seconds is way bigger than the one for the seconds 30 seconds so therefore clearly the bus traveled further so for the first mark state the fact that distance is given by area under the graph and then for the second might compare the two areas under the line and you're done question for the diagram shows some people waiting in a cute supermarket the queue moves forward each time a person leaves the checkout person expands 7 minutes in the queue before reaching the checkout and the graph shows how distance changes with time for person X so it's the last person in the queue and notice that it is a distance time graph so what is the initial length of the queue and we're looking for that in meters so all you have to do is read off here on the y axis so read along and you'll see if my pen wasn't as fat that it is six point one meters they explain how you could use the graph to work out the number of times person X is stationary so explain is going to be a very crucial word here and we also need to work out the number of times the person is stationary so station mu means that they don't move so when aren't they moving well it's all the flat portions of the graph so that's one two three four five six seven so you're going to say seven times that they were stationary and we know this because the flat part of the graph indicates zero speed state the equation linking average speed distance move done time taken so out of the way I'm going to write my formula triangle DST so therefore average speed equals cover the ass distance moved over time taken part to calculate the average speed of person X in the queue give the unit don't forget to give the unit so the distance moved we know is six point one meters the time is seven minutes don't get caught out here I know the graph looks confusing but it tells us up here that the person spent seven minutes in the queue I'm going to multiply it by sixty because the SI unit for time is seconds so obviously there are 60 seconds in a minute hence why I'm timesing it by sixty pop that into your calculator and you'll get a value which rounds to 0.01 five to three significant figures and we know that the distance was in meters I've already told you that I've converted to seconds which is why the unit here is meters per second we now need to discuss the difference between weight and mass so people constantly get this confused they talk about how much they weigh when actually they're talking about their mass and I'm going to explain what I mean by that so weight first of all is given by the unit and which stands for Newtons mass is given by the unit kilograms and so surely we can see that they have different units now it's worth noticing that your mass is unchanged it doesn't matter where you stand with which planet you're standing on where you are in space your mass will remain the same so if your mass is 50 kilograms on earth it will be 50 kilograms on Mars and that's because it's really a description of what you're made up of however with weight weight has to take into account gravity and therefore when gravity changes your weight will change if we look at the equation linking the three you find that weight equals mass times gravitational field strength so if you have a mass of 50 kilograms you're standing on the earth in which has an approximate gravitational field strength of 10 your weight will therefore be 500 Newtons so this would be the case on earth however on the moon if we do the same calculation we find that although your mass is still 50 your gravitational field strength is hugely reduced on the moon to in fact only 1.6 meaning that your weight on the moon is only 80 Newton's so this is a huge change your weight has drastically decreased on the moon whereas your mass has stayed the same so there in everyday life we talk about how much we weigh we say 50 kilograms remember that's inaccurate and they were actually discussing our mass and as long as you can use this equation weight equals mass times gravitational field strength they'll have no problems we now need to look at the topic of force so just remember first of all the effect that force has on an object and that can be that the force changes the object speed it can change the object's direction or it can indeed change the object shape you need to be able to list the different types of force so I've written them out here and now we just need to have quick chat about what all of those things mean so first of all notice that some of these forces are contact forces and these are forces which act between two objects that are actually physically touching each other non-contact forces is obviously as the name suggests when they don't touch so let's actually have a look at this normal reaction first of all because that's quite a strange one this normal reaction force or reaction force or normal contact force it's all the same thing that's when an object is on the ground and it experiences a force which is perpendicular to the surface and what that means that's where the word normal comes from because remember in the light topic a normal line is the line for example drawn like this so here's your glass block and here are some normal lines because they're 90 degrees to the surface of the glass block so in a similar way the reaction force is felt perpendicular to the surface and I'll show you an example of that later with a car so don't worry too much now friction is a nice straightforward one that's when two objects slide past each other they experience a friction force so for example a toy car sliding down a slope will experience friction where its wheels touch the slope air resistance or drag that's to do with objects moving through the ass it could be a car being driven along the road and our particles collide with the car creating a small force which acts to slow it down the faster the cars traveling the more particles that will hit per second hence air resistance increases and that's why things like cars have to be streamlined to reduce air resistance looking at non-contact forces so let's start with the magnetic force and that is experienced by any magnetic material inside magnetic field do you remember that opposite magnetic poles are trapped so North and South Poles will attract like poles such as to north poles or to south poles repel and electrostatic forces all to do with static charge so we're talking about the buildup of charge and it's experienced by any charged particle that's held within an electric field so a gravitational force as the name suggests is to do with gravity and it's experienced by any mass which is found within a gravitational field and remember these muscles may be attracted towards each other due to this gravitational force the easiest example here is the Sun and the earth they're both masses they're both very large objects and they're held in position to you to the gravitational force between them weights I've already touched upon remember that is a force acting downwards from any object and it incorporates both the mass and gravitational field strength up thrust this is when we're talking about water say for example a boat sitting on water although its weight is acting downwards there's the force of the water pushing back up so it's the equivalent of the normal reaction force so we call this up thrust and if weight and up to us to equal then we know the boat will float the nuclear force is as Anna suggested with the nucleus of atoms or the nuclei of atoms and it's the strong attractive force between the protons and the neutrons within the nucleus that helps hold the nucleus together remember that force is measured in Newtons and that you often see a force diagram and that's basically an object which is moving and it will have arrows and the size of the arrow represents how large the forces so obviously the larger the arrow the larger the force remember in your textbook I often talk about balanced forces that is when two forces acting on an object they'll be acting in opposite directions to each other and remember that they have to be the same size for them to be balanced forces and that basically means that an object which is standing still I stationary it won't speed up it will stay exactly as it is and it also means an object which is traveling at a certain speed when it has balanced forces acting on it will continue to travel at that speed it won't speed up and won't slow down so therefore could move my unbalanced forces it makes sense so one of the forces opposing the other force is larger than the other so if the object is stationary it will start moving and if the object is traveling at some speed only the speed up or slow down so one of these forces that we're talking about I'm going to use the example of a car driving along the street to help illustrate this so you have a car that sat on the tarmac and it's driving so the forward force is going to be the driving force from the engine and that will be causing the car to neither accelerate or just carry on traveling at the same speed opposing that driving force will be several other forces first of all air resistance otherwise known as drag now what is that basically if you've got a car moving you've got air whistling past it and these air particles they'll collide with the car and they've generate a tiny tiny force which acts in the opposite direction to the direction the cars traveling and by doing that they oppose the motion of the cast they act to slow it down and we have lots of other forces opposing motion so there's friction remember friction is the force that occurs between surfaces so friction of this example will be between the car wheels and the road so remember it's that friction which is useful because Allah allows the car to grip onto the road and in certain conditions like icy conditions wet conditions or if the ties have been too worn you'll decrease the friction between the tires in the road and that can lead to dangerous occurrences like the car skidding so a bit of friction is important you have other forces acting on the car you have weight remember that's the downward force due to gravity and don't forget this force it's called the normal reaction and that occurs between the tires and the road surface and it occurs upwards so perpendicular to the road and basically all the normal reaction is is it's the force which stops objects kind of being forced into the earth so acts against gravity it's quite a hard one to imagine but just remember that it occurs at 90 degrees to the surface you reward to a bottom of velocity we tend to use the example of a parachutist jumping out of an aeroplane and you'll often see lots of diagrams of areas of different sizes I'm going to try and talk to you about that now so let's start at the top was starting in our aeroplane and our parachutist is looking out he's about to jump the moment he jumped the only force acting on him is went so that will cause him to accelerate towards the Earth's surface now the faster he accelerates via the bigger the air resistance because remember as he's dropping he's going to be hitting lots of air and that those air particles are going to be acting in the opposite direction to his motion trying to slow him down and the faster he travels the more particles will hit him per second so the overall force of drag or air resistance will become very large so at a certain point you will find that the size of the air resistance or the drag will match the size of the weight force acting downwards and we call that terminal velocity because all that means is that the two forces are balanced and the parachutist will no longer accelerate he'll just continue falling at a constant speed and that is what time the velocity is basically mean accelerating or decelerating just traveling at a constant speed before too long the parachutist will choose to open his parachute because he won't obviously want to splatter on the ground we knew this is parachute you see a massive increase in the surface area of the parachutist and therefore when more air particles will be will be trapped inside the parachute and therefore air resistance won't increase hugely and he'll jerk upwards as a result of that and you'll see that he'll slow down however because his speed decreases that actually causes air resistance to decrease because if you think about it the slower he now travels the fewer air particles will be hitting him and opposing his motion and therefore he'll slow down and eventually his weight and the size of the drag air resistance force will become the same and we call that time we've lost again because he's now traveling at a constant speed now remember that tunnel city will be a much lower speed than the initial one and that's due to the fact he's opened up his parachute another physics equation you need to be aware of is farm so f stands for force a stands for acceleration and M stands for mass so let's work out the various variations so force equals we can see that it's acceleration times mass four after acceleration half of that up you can see that it is force divided by mass and lastly mass equals force divided by acceleration touching quickly on the units mass should always be in kilograms forces Newtons it's acceleration is meters per second squared so make sure you have that sorted and we'll look at a couple of examples now so in this question we're calculating the resultant force required to accelerate a 30 kilogram object at 1.5 meters per second squared say yeah we have mass we have acceleration we're looking for force so force equals acceleration times mass this is a simple experience of substituting in those values so 1.5 times 30 which gives you a value of 45 Newtons question 2 the force on a moving object is 1,000 Newtons calculate the mass of an object if it is accelerating at two point five meters per second squared so we've been given the force in the acceleration masses given by F over a our forces of thousand Newton's divided by the acceleration which is two point five giving us a value which is 400 don't forget your units it is in kilograms a student investigates terminal-velocity she uses a tool glass tube filled with oil she drops the metal ball into the tube and the ball falls through the oil use ideas about forces to explain how a falling object can be to terminal velocity doesn't matter what this question is if it's someone jumping out of a plane or a ball being dropped into a tube of oil if it mentions terminal velocity this is your perfe answer so first of all you want to state that the ball has a weight and that will be its downward force acting upwards will be the force of drag as the ball accelerates the drag force will increase and eventually the weight will equal drag at this point the ball no longer accelerates it travels at a constant speed and there is no further acceleration and this means that terminal velocity has been reached so that's your powerful answer try and write it in sentences I've written it like that for ease of iPad use describe how the train could find out if the ball each is tunnel velocity as it falls through the oil in your answer you should include the measuring instruments that the student will need the measurements she should take and how she could use her measurements to find out if the ball has reached terminal velocity you may include a label diagram in your answer so clearly we need to use a timer to time how long the ball falls for and we need to use a ruler to make sure that the ball is falling over the same distance every time in terms of the measurements taken you need to take a measurement of time for the amount of time that it took for the ball to pass between two points you obviously wants to work out that distance using your ruler and then repeat and calculate an average to increase the reliability to make it even more specific you could have used a light gate and then lastly once you've worked on the distance on the time you can obviously calculate speed using speed equals distance divided by time so I want to quickly talk to you about Hookes law now Hookes laws are pretty boring experiment whereby a guy called hook amazingly originally hung various weights off a spring and measured their new length of the spring and then obviously as more weights were added this spring got longer and then he plotted a graph which was force and it's okay to plot force because remember for some weight have the same unit which is Newtons against the extension and you see on the graph that it should be a proportional relationship which means that as the length as the weight increases the length of the spring increases which makes sense then you'll find that the line distorts and that's because we're no longer increasing proportionally and that's because the elastic limit of the spring has been reached it's deformed it's bent out of shape and it won't return to its original length so that's what underpins hopeful now we're going to look at a past exam question on it so a street investigates whether spring a base Hookes law she is separate or shown in the photograph which additional measuring instrument does the student need for the investigation I've told you it's all about measuring the length of the spring so we need a ruler explain how the student can investigate whether the spring a Bayes Hookes law so we're basically looking for experimental details on what they're going to do so first of all you want to measure the original length of the spring using that meter Lulla and then we're going to add a known weight to that hook and measure the new length of the spring and then we just repeat the process using a range of different weights so we can be up to 20 Newtons 30 Newtons 40 Newtons or we could repeat at each weight because remember repeating calculating an average is really important and that's worth mark for just pointing out that particular experimental detail so we're going to start by looking at the for the various components within a circuit then we're going to move on to looking at the graphs Ohm's law and I'm going to finish with all the calculations because there's a lot to do on that but like I said we're starting with the electrical components so let's start with drawing a cell first of all and remember it has both a negative and positive terminal the positive terminal is the longer line if you have two or more cells together such as this you have a battery what's lighting up inside a circuit is known as a lamp or a bulb and we draw it using this particular symbol next up we need to draw a resistor this is quite straightforward because it is just a rectangle now if you draw a rectangle but this time draw an arrow going to it that tells you it is a variable resistor which means you can alter its resistance of the circuit and then underneath we're going to drill what I call the hockey stick component and this is a thermistor it is a temperature dependent resistor looking at diodes now it looks a bit like the play button a diode is special because allows the current to flow in one direction only given by the direction which the arrow is pointing this means that the current in this case is moving to the left if we add a couple of arrows to this it is a light-emitting diode so that's an LED and you find those on your remote controls for example next up if we want to measure the current of a circuit we're going to use an ammeter if we're measuring the voltage we're using a voltmeter and then we can add a fuse to our circuit and now remember a fuse is a safety device it melts when the current is too high breaking the circuit remember if you're asked the difference or the advantage of using a circuit breakers or post refuse is that a circuit breaker is much faster and easy to reset why because look at the fuse the wire is going to melt and so you're going to have to replace the whole thing before you get your circuit working again let's make a couple of notes on how you add various components to a circuit so I'm just going to draw a simple circuit containing a battery and a light bulb and now I'm interested in working out the resistance of this circuit so remember we're using this formula triangle V IR to work out resistance you just covered that R and have a look at what's left so it's V over I i stands for current it's given by the letter i' because it used to stand for intensity of currents so historically speaking we've always used I to represent it now in order to work out resistance I therefore needs to know both the voltage and the current it is absolutely essential that you know that the voltmeter is added in parallel around the component in question that in this case will be the bulb so you add it as an extra branch and the ammeter needs added in series which is why I'm gonna pop it here it doesn't really matter where it goes but it needs to be in series they often give you questions with various diagrams asking you what the problem is and quite often you'll find that the voltmeter and the ammeter aren't in the correct place so do you make sure you know that remember the units for resistance is the ohm whereas for current it's amps and for voltage it is volts sometimes they want to know why the resistance increases when the temperature increases and I'm just going to quickly show you why so if I draw a wire us remember wire is made out of positive is made out of metal which is made up of positive metal ions and negative electrons now what happens if you heat that wire obviously those positive ions are going to vibrate more because they contain more kinetic energy and therefore it's going to impede or inhibit the flow of electrons through the wire so if they ask you why does resistance increase with increased temperature in a wire you're going to say it's because positive ions vibrate more stopping the flow of electrons due notice however that thermistors behaves differently as temperature increases a thermistors resistance decreases and that's because it's not actually made out of a metal you don't need to know why but do remember that as the temperature increases the resistance decreases and while we're talking about resistors let's look at this resistor which I've already forgotten to mention but it's fine this is a light dependent resistor now when the light levels increase the resistance decreases and this is used in your street lighting outside so as it gets dark this light dependent resistor this LDR is the reason why the lights come on there were a few graphs I want to talk through now now do you remember Ohm's law and that states that the current through a resistor of constant temperature is directly proportional to the potential difference across the resistor and various components are Baker Ohm's law and some do not obey Ohm's law now a wire obeys Ohm's law and you'll see that because you can see it's straight line through the origin so clearly you can see that as the current increases the voltage increases and that's a constant temperature so a wire obeys Ohm's law you get a very different shape when you show a filament bulb so a light bulb this is not a proportional relationship we've got a sigmoid or shape an S shape and the bulb therefore does not obey Ohm's law because there's no direct relationship between the two and then lastly and very strangely the diode looks like this again it doesn't obey Ohm's law and the reason it's this shape the graph is because the diode only allows current to flow in one direction only we just need to discuss current and voltage rules for both a series and parallel circuit so notice that in a series circuit the current is the same everywhere whereas the voltage of individual components adds up to the total voltage and I'm going to show you what that actually means now so I'm drawing a battery here which let's say it has eight volts across it then we've got a light bulb here a regular resistor here and I'm just going to complete the circuit so if I tell you that the current here is 12 amps because I've said that the current is the same everywhere it doesn't matter if an ammeter got added here here or here all those readings would be 12 amps however with the voltage if you added volt meter's here and here their readings would not be 8 volts let's say that this was 5 volts the reading that means that this reading here must be 3 volts and that's due to that second point that the voltage of the individual components adds up to the total voltage the opposite is true in a parallel circuit here you find that the voltage is the same everywhere whereas the count of the individual components adds up to the total current that means that each of these light bulbs here will have 12 volts going through them and that explains why with a parallel circuit how if you keep adding extra bulbs the brightness remains the same and that's because they receive the same voltage however it will mean that your battery will run out three times as quickly as if there was only one in terms of the current pretend that was a 2 amp bulb this was a 2 amp bulb well we know because it has to add up to the total current this lamp down here is slightly different in that it has a current of 1 arms you so a 4 volt battery can supply power or 5 amps for 20 minutes before charging calculate how much charge the battery can provide before it needs to be charging at this point what I always do is I draw out my formula triangles because why not it's good to get your head nice and into the question and knowing that you actually know stuff that you can use so the first one is voltage is current times resistance the next one is charge is current times time and then finally the third electrical triangle that I am use is work done is voltage times charge and just remember that the units of charge are coulombs so at the end of a question write a capital C and they're really fussy about how you write the units to make sure it's a capital C rather than a lowercase C in order to get the mark and remember I just said that resistance is measured in ohms and the sign for an ohm is like this which I'm drawing badly anyway let's look at the question then calculate how much charge the battery can provide before it needs recharging so we're looking for a triangle that has Q net so there's two of those and what else ever I've been told well I've got the current because I've been told five amps and I've been given the time which is 20 minutes so what I'm going to use is the Qi t triangle so I'm going to write out because it's always good practice to do this Q equals I times T is five okay T is 20 minutes but remember that's not very scientific so we're going to convert that into seconds by doing 20 times 60 and the answer here is 6,000 and like I just said the units of charge are coulombs so I'm going to write a capital C here be each Coulomb of charge from the battery can carry 3 joules of energy calculate how much work at the battery can do before it needs recharging okay so for Part B you're going to use the formula W equals V times K V has been given as 4 and Q is something that I just worked out which is 6000 so what's 4 times 6,000 well it is 24 and work done is measured in joules so there's the answer right there okay let's look at another type of question okay so I've drawn a horrendous circuit here but hopefully it will still manage to help UT some way so this is an example of the sort of thing you get in the exam we can see that we have a series circuit with a battery made up of three cells and a miso of the reading of Nohr point five amps and three regular resistance in series we've been given two of their resistances we don't know the third one and a voltmeter has been added in parallel around resistance number two so calculate the total potential difference across the battery okay so all you have to do here because remember potential difference is the same as voltages add up those three readings so that's 2 plus 2 plus 2 which is 6 volts nice and straightforward ok work out the total resistance so it'd be tempting here to try and add up all the resistances of the individual resistors you can't do that because you don't know the resistance of a resistor three so we're going to have to do this a different way and we're going to use this equation triangle so resistance is V divided by I the V is 6 which I just worked out I is not point five given by the ammeter and therefore the answer is 12 and the units are ohms okay finally calculate the resistance of r3 so if we know that the total resistance is 12 ohms but we've been given R 1 and R 2 that's 6 ohms that tells us the difference between those two values will be r3 s value so 12 type 6 there's obviously 6 and that is 6 ohms 3 the first row shows and that'll appliance called a toaster the toaster has a power of 1800 watts when operating a voltage of 230 volts state the equation linking power count and voltage so I'm going to put my formula triangle nice not the way over here it spiv so P at the top current and voltage in the bottom so what is the equation it is power equals current times voltage part to show that the current in the toaster is about 8 amps so current equals power divided by voltage always had the equation I'm using we know that power is 1800 dividing it by 230 to give seven point eight three to three sig fig which is approximately eight amps which fuse vation would be suitable for the toaster remember the fuse rating needs to be slightly higher than that calculated current and so it's not ideal because 13 is a lot higher but you can't say one three or seven you can't say seven because it's lower which means it would constantly have melted when the toaster was in use which is why D is the correct answer here be the toaster uses main electricity mains electricity provides alternating currents describe the difference between alternating current and direct current so learn these definitions off by hearts an alternating current is one where the current continuously changes direction whereas the direct current is one where the current flows in one direction only the photograph shows an electric heater the power of the heater is 2,000 watts the heater was connected to a 230 volts main supply state the equation linking power current and voltage and I can remember that is pip so therefore power equals current times voltage calculate the current in the heater so rearranged so that current is power divided by voltage power is 2,000 watts divided that by 230 volts and you get an answer which is eight point seven amps which of these fuses should be used with the heater so you're looking for one which is higher and not too high compared with the current you've calculated and that will have to therefore be 13 amps deep because it's the only current higher than the one we've calculated the two heating elements can be connected in series or parallel describe an advantage of each method so with parallel the obvious advantages that you have independent control so you can turn on and off the heating elements independent of each other so you could just have one on or both on at the same time the series one is a bit more of a state the obvious here you can use a single switch only to control both heating elements some electrical appliances a fitted with an earth wire described found earth wire acts as a safety feature that is worth four marks so state that first of all the earth wire is connected to the metal casing and that if the casing becomes alive the earth wire provides a low resistance path to obviously the earth and then you can talk about the use of a fuse which is attached to the earth wire so that increase in current will cause the fuse to mount breaking the circuit which cuts off the supply the explain why this heater should be fitted with a NOS wire and the obvious thing is because it has a metal casing and we met and remember metals are good conductors of electricity so the wave topic let's try and cover as much of this as possible there are two types of wave you need to know about transverse and longitudinal waves learn the perfect definition for both transverse waves of vibrations occur perpendicular to the direction in which the wave was traveling key examples here are water waves and light waves and any member of the e/m spectrum infrared radiation ultraviolet x-rays etc longitudinal waves vibrations this time occur parallel to the direction in which the wave is traveling your key example here is a sound wave being prepared to draw a longitudinal wave will notice that there are periods of refraction and compression so it's like a slinky but it comes close together that's compression where it moves further apart that's a rarefaction now the wave equation states that wave speed equals wave frequency times wavelength waves to be measured in meters per second frequency measured in hertz and wavelength measured in meters what is the frequency of the wave well it's the number of waves per second if you're labeling a wave be prepared to draw the amplitude which is from either the middle ranks at the top of the wave or to the bottom of the wave it's not from top to bottom that's two times the amplitude the wave length is the distance between two peaks or two troughs the time period of a wave is the time taken to produce one wave and it's given by the equation that frequency equals one over time period so let's talk about reflection that's all to do with waves bouncing so remember the key thing here is to no difference between the angle of incidence and the angle of reflection so the wave coming in and hitting the substance is the incident ray it bounces off and what you find is the angle at which it bounces off so that angle of reflection will equal the incident angle don't forget to lower your normal line which is a line that's like an imaginary line drawn at 90 degrees to the boundary surface refraction is all about a way of changing direction when it enters a new medium and that's due to either slowing down speeding up so it's due to a change in wave speed what you find here is that if you have a light wave entering a glass block it will slow down and it will Bend Ward's the normal on exiting the block it will speed up again and Bend away from than almost so be prepared to draw that they'll ask you to draw it for IGCSE headaches and lots of different shapes who do try and practice that before the exam and also be aware of what happens when water waves move from a different depth so when they go from deep water you find that they're traveling really quickly and that the waves are very far apart from each other as they enter shallower water they slow down and the waves come closer together and you'll actually see the wavefront getting closer together if you're struggling to remember that just remember cars on the road there'll be further apart when they're travelling nice and quickly and then when you're stuck in a traffic jam and they're traveling slowly they're basically on top of each other but now an image that can be produced on a screen is known as a real image one which cannot be produced on the screen is known as a virtual image you need to know the properties of an image inside plane mirror now remember that clearly the image is going to be the same size as the original object it's going to be laterally inverted which means your left and right sides will have swapped over in the mirror go check in a mirror if you don't really understand what I'm saying it's going to be the same color and it's going to be the same distance behind the mirror as you're standing in front of it now the equation for the package and the refractive index is n equal sign I over sign R which you'll have to learn now sign I so remember is the incident angle so you just need to pop that into a calculator with the sign in front of it and so now that's the angle of refraction so again pop into a calculator but first of all pressing the sine button now the critical angle is something there like asking you about and it's all to do with the angle of incidence so every type of medium every type of substance has its own critical angle now if the angle of incidence is less than the critical angle you get both refraction and reflection taking place if the angle of incidence is the same as the critical angle you get a refraction which occurs along the boundary if the angle of incidence is greater than the critical angle you get what's called total internal reflection so you don't get any refraction all the light is totally internally reflected and they make use of this in optical fibers now to calculate critical angle you simply need to do sciency equals and making sure you inverse sign on your calculator to get the correct value for C dispersions all to do with light splitting up and spreading out so if you get white light remember it's made up of lots of different colors if you shine it into a prism it will split into those colors remember the order of the rainbow and that'll help you with knowing what colors the likes fits into so Richard of York gave battle in vain red orange yellow green blue indigo violet now red is refracted the least because it's so down the least violet is refracted the most because it was traveling the fastest and therefore slows down the most what is an echo well it's a reflected sound wave remember ladies echo sounding for working out to the depths of the ocean so there's some dance in some waves they were called the time it takes for the sound wave to be transmitted and then be received again by the transmitter you use the equation speed equals distance over time so you know the speed of the sound wave you've recorded the time just make sure you have the time because obviously if you use the full time then that's the time it took tip for the wave to hit the bottom and come back up whereas the distance is only from the transmitter to the bottom which is why you have to have their time five eschew uses of ik tango glass block to determine effective index of glass the diagram shows a ray of red light in there as it enters the glass block @p the normal @p is shown as a dotted line which as we would expect is perpendicular complete the diagram by drawing the way that continues inside the block labeling the angle of incidence and the angle of refraction and drawing the Ray that leaves the block so use your ruler here and a pencil so remember as it enters the block it enters the more dense medium so it bends towards the normal which is why I'm doing it here we need to draw a second normal line down here try and draw that more straight than I have and then remember as the Ray leaves it is again parallel to that Ray that came in which is why I'm doing it at this angle now we must label the angle of incidence and the angle of refraction so the angle of incidence is between the normal and the incident ray the angle of refraction is going to be hard to show that that's in there and that's between the normal and the way that has been refracted the student measures values for the angle of incidence and the angle of reflection R so I is given as 60 degrees I was given as 34 degrees so we need to complete the table wine setting values for sine I and sine R so that's quite straightforward just put into your calculators sine 60 and when you've done that that is zero point eight seven to two decimal places put into your calculator sine 34 and that is zero point five six to two decimal places state the equation linking refractive index angle of incidence and angle of refraction remember refractive index is given by n so it's n equals sine I over sine R so in terms of calculation for active index sine I is 0.87 sine R is zero point five six and when you put that into your calculator you get a value which is one point six two two significant figures how should the student continue the investigation to obtain a more accurate value for the refractive index of gloss so that's worth three marks to make three separate points so the most obvious point to make is to increase the reliability you want to repeat and calculating average you want to vary the angle of incidence more secret do 50 degrees 70 degrees 80 degrees and then next you could draw a graph plotting sinaï against sine and remember that the gradient will give you the refractive index the electromagnetic spectrum now which is a little sub topic of the waves topic I do like this topic remember that it is a family of waves and they vary just in terms of their frequency and their wavelength so let's go through those ways first of all so starting with the longest wavelength wave so wait which looked more like this so they have long wavelengths because you remember the wavelength is the distance between two peaks or two troughs as opposed to having short wavelengths whereby the wavelength is this big as opposed to this big so we starting from the longest wavelength that is radio waves then we have microwaves infrared radiation visible light ultraviolet x-rays and gamma rays and I'll provide a link below to this video which I love one of my two T's told me about it a couple years ago and it's I think it's owned by some South Korean guys if you start playing it at thirty Seconds listen to the chorus through three times and you'll have to order nailed in your head otherwise I'm sure there are lots of mnemonics that people can remember and comment below if you know of a good one times the frequency clearly gamma rays will have the highest frequency because there's more waves per second with gamma rays because they're much closer together where is microwaves and radio waves will have a much lower frequency because their waves are much further apart the key point to notice with this topic is the various uses of all of these so we'll start with radio waves remember these are used in communication microwaves are also used in communication so satellite communication they're also obviously used in cooking food most of us have microwaves in our kitchen then we have infrared radiation and that is also used in communication and in this case we're talking about remote controls to communicating between the remote control that you're pointing at the TV for example so infrared radiation is being given off there remember we've met infrared radiation when we're talking about the heat topic so conduction action radiation because infrared radiation is simply heat being given off from objects and therefore everywhere variation is the type of radiation used in ovens because obviously they get hot to cook our food and they are giving off infrared radiation visible light as well as the usual use of so that we can see stuff with them it's also used in optical fibers and photography now we're getting down to the other end of the spectrum so when the wave start getting much closer together the next way we're going to be looking at is ultraviolet so UV remember these arrays that come from the Sun they have various uses such as tanning beds so Sun beds that will have UV rays being emitted but also you can use it to check where the banknotes have been forged or not to hold up to the UV light and you can tell if they're authentic then we're looking at x-rays obviously they're used in medicine to create images of the human body and lastly gamma rays gamma rays are used to sterilize surgical equipment because they're such high energy they kill things effectively so that could be killing bacteria on surgical equipment it could be killing cancer cells so used appropriately they're very useful if they used inappropriately they can actually cause cancer so that's worth noticing the way they'll ask the questions is it will say stuff like microwaves are used in communication named two other ways also used in communication you could have said infrared radiation you can set radio waves all visible so be aware here what dangers associated with infrared radiation well because it's effectively heat if they gets too hot it can cause skin burns if you touch it dangers associated with ultraviolet that will be skin cancer because again if used inappropriately that can cause cancer as well as the rays from the Sun if we're exposed to them for too long it can cause cancer how can we reduce danger from exposure to ultraviolet well wearing sun cream wearing sunglasses to protect our eyes limiting our exposure time coming up wearing clothes protect ourselves from x-ray we need to limit our exposure time hide behind LED screens we're protective clothing and the same is true of gamma rays you really ought to be exposed to these rays for too long they could ask you what all these Rays have in common and that is that they are all transverse waves so in all cases vibrations are cut perpendicular to the direction which the waves traveling remember that's what a fad definition of a transverse wave they clearly all transfer energy they may all be reflected refracted and diffracted so they can all bounce of objects they can all change directions they go through a different medium and lastly they travel at the same speed which is 300 million meters per second one thing they have added to the specification is the difference between x-rays and gamma rays so remember x-rays are made when high-speed electrons are stopped whereas gamma rays are emitted from unstable nuclei which we'll look at more closely in the radioactivity topic in terms of their properties remember that gamma is more penetrative goes further travels further and gamma has the shorter wavelength because it has a higher frequency the table shows the main sections of the e/m spectrum so we've got gamma rays x-rays ultraviolet visible infrared microwaves and radio waves state two sections of the spectrum that are used for communications so you're looking for the long wavelength and which is radio waves microwaves or infrared or visible any of any two picked from those four will be suitable state two sections of the spectrum that are used for cooking clearly microwaves most people own a microwave secondly it's infrared because remember infrared is just generally heat so an oven uses infrared radiation the area below the table shows the direction of and don't look at the answer to try and work it out and then spot the answer in the list below so it's pointing towards the radio wave and which means it's waves with increasing wavelength so have a look down in it is d the radio station broadcasts at a frequency of 200 kilohertz the wavelength of the radio waves is 1,500 meters state the equation linking wave speed frequency and wavelength so wave speed is given by V frequencies F lambda is wavelength so calculate the speed now make sure you convert those units so kilohertz needs to be in Hertz so times by a thousand then we have our wavelength which is fine cuz it's in meters and when you've done that you've got an answer which is 300 million meters per second don't forget the unit okay new for this specification is the types of energy they've kind of changed the naming system so some have stayed the same and some are new so we're going to go through each of them in turn talking about what they mean and some examples so starting with chemical energy this is to do with energy stores and its associated with chemical bonds and really your examples here are things like food remember food is the storage of energy the same is true for batteries kinetic energy this is to do with moving an object so anything that has movement has kinetic energy so a man running down the road a bus being driven along the street they both have kinetic energy gravitational energy as the name suggests is energy associated with an object gaining height so anything that has been lifted will gain gravitational energy for example a chairlift a ski resort an aeroplane these will have gravitational energy and Apple being picked up for example next up elastic energy this is the energy stored when an object is stretched squashed or twisted rubber bands of the obvious place here catapults balloons that have been inflated anything that you distort and then pings back to its original shape will contain elastic energy nuclear energy will become very important when we look at nuclear fission because this is the energy associated with those reactions so remember the fuel uranium-235 which you do need to know that is a huge store of nuclear fuel and therefore nuclear energy thermal energy as the name suggests is to do with heat anything that has gone hotter has gained thermal energy so a hot cup of tea for example magnetic energy is new for you guys and this is the energy stored when light poles are pushed closer together or when unlike poles are pulled further apart so light poles remember is two South Poles being pushed together unlike poles would be the North and South Pole so just name any magnets here so just a simple bar magnet a fridge magnet the e puts on the fridge door these would all count as magnetic energy stores and lastly electrostatic that's the energy stored when light charges are move closer together or when unlike charges are pulled further apart so very similar to the magnetic energy and your example here is it's hard but it's things like clouds remember when there were lightning storms there's a huge buildup of a static charge under Graaff generators the same place whether you build up static charge you will have electrostatic energy the diagram shows some electrical appliances which appliance is designed to transfer electrical energy to thermal energy so we're putting in electricity we're getting heat out of it it is clearly the kettle B which appliance is designed to transfer electrical energy to kinetic energy so again we're putting in electricity we're getting movement energy out which would be the food mix that a in all appliances energy is conserved what is meant by the phrase energy is conserved and that is the energy cannot be created or destroyed it is simply converted from one form into another the lamp has an efficiency of 20% explain what this means and that means that 20% of the energy input has been transferred usefully so in the case of the food mixer 20% of the electrical energy in will have been converted to kinetic energy or you could have argued that 80% of the energy input has been wasted draw a label Sankey diagram for the lamp okay so thank you diagrams always look like this now you do find that a lot of it is wasted so that's why the wasted energy arrow down here will be much broader than the useful energy and now let's label all of them so the lamp coming into that will be electrical energy the useful energy out will obviously be light energy and then they'll be wasted energy in the form of heat because do notice that lumps get pretty hot because we haven't been given any numbers you can't add any numbers so don't worry about that we now need to look at efficiency so using this example a filament bulb was supplied with 80 joules of energy tendrils of energy was output as light the rest was wasted calculate the efficiency of the light bulb you need this equation so efficiency equals useful energy out over divided by total energy in and I like to make it a percentage so ties by hundred that's not altogether necessary so useful energy out we know was the light so that's ten total energy input was eighty times it by a hundred so you can pop that into a calculator or just cancel it down like I've just done so the efficiency is 12.5% a hamster of mass 40 grams runs our / 2 meter curtain in 5 seconds calculate its power so we have mass which I'm going to immediately convert into kilograms make sure I don't make any errors so that becomes zero point zero four kilograms we have distance which is 2 meters we have time we're looking for power now there isn't a direct equation that links these components now this questions actually more complicated than it looks because you need quite a few equations as there's no equation which directly links mass distance time and power first equation we need is weight equals mass times gravity the next one we need is a formula triangle which is work done equals Force Times distance and the last one contains power which after all is what we're after which is work done is power times time well is the common factor linking the two formula triangles well it is work done so we need to calculate work done first of all which is Force Times distance unfortunately we don't have the force so we're going to have to work that out and this relies on you remembering that force and weight have the same unit so if we work out weight then we can work out the force so we need this equation first of all which is weight is mass times gravity I've already told you that the mass is 0.04 gravity on earth is approximately 10 so therefore the weight is 0.4 Newtons now we're going to calculate work done using the equation Force Times distance force and weight have the same unit which is y can substitute in 0.4 as the force distance is 2 as given by the question so the work done is 0.8 joules and then finally we can work out power by doing work done so the time how look how I've laid out my answer with all my equal signs lined up with all my working out shown so the work done we know is 0.8 I'm only writing here cuz I'm running out of space divided by time which is 5 so that becomes 0 point one six don't forget your units for power which is what's right I'm going to go through some miscellaneous calculations to show how you should be approaching questions if you're not quite sure which equation to use so my first piece of advice is the moment they tell you to start during your exam turn over to a blank page and start scribbling out all your formula triangles so you're pretty much making yourself your own personal formula sheet even though that will probably take you about a minute it will be totally worthwhile because it means when you get to a particular calculation of which there are many in the physics exam you don't need to be scrambling around in your brain for the correct one you just refer to your formula sheet and it should literally just be sitting there waiting for you so let's have a look at what we have here though so student pushes a trolley of weight 150 Newton's up the slope of length 20 meters the slope is 1.2 meters high calculate the GPS that's the gravitational potential energy of the trolley and calculate the work done by the student so what do we have here let's identify look at the unit it's a Newton which means it's both weight and force we know the slope length is 20 meters and we know that it is 1.2 meters high so gravitational potential energy is given by mass times gravitational field strength times height we see an immediate issue which is that we don't have the mass of the object we only have its weight so we need to do a preliminary calculation using this formula triangle which is weight equals mass times gravity we're looking for mass so that's going to be weight divided by gravity now the way we've been told is 150 Newton's gravity on earth is approximately tan you could put a 9.8 but I'm going to write 10 and therefore you're going to write the mass as being 15 kilograms now we're ready to use the original equation so mass is 15 gravity I've just said is 10 the height it says that the slope is 1.2 meters high hence 1.2 is substituted in here so once I've substituted that in I get a value which is 180 it's an energy value so it needs to be in joules so I've rubbed the best out so we've got more space so and B we're calculating the work done by the student if she pushed the trolley with a force of 11 Newtons so we have work done we have force so the formulas on Google so we need this time is work done equals Force Times distance so we're looking for work done let's write out the equation equals Force Times distance the force we know is 11 Newtons the distance look higher up in the question she pushed it up a slope of length 20 meters that's why we substituted in 20 here pop it into the calculator and you know that it is 220 work done remember has the same units as energy which is why I'm putting 220 joules next equation I'm interested in is kinetic energy which is half of mass times velocity squared I prefer not to put this into a triangle I think it's easier if you keep it exactly as it's written and I'll show you how to calculate the different parts so you can actually see that it can be rearranged easily in this first question we're being asked to calculate the kinetic energy of a tennis ball traveling at 46 meters per second with a mass of 500 grams so as always write out our equation which is ke is half MV squared be careful with your units because 500 grams isn't in kilograms so I'm going to put that into kilograms so remember 500 grams is is 0.5 kilograms so start substituting in your values so it's 1/2 times 0.5 times 46 squared so start to simplify so half of 0.5 is obviously 0.25 46 times 46 or 46 squared is 2 1 1 6 times that by 0.25 and that gives us a value which is 529 it's an energy value so it's in joules calculate the velocity of a bus traveling through town with a mass of 5040 kilograms and kinetic energy of I'm not gonna read this number of five hundred and twenty seven thousand six hundred and forty-three jaws so writing out the equation ke equals 1/2 MV squared we know the ke this time so I'm just gonna pop that in here I find it easier to answer these questions if I rearrange later so half of mass so that's 1/2 times 504 oaths and we're looking for velocity so we'll keep that as B squared the easiest thing now is to work out half of the mass which is two thousand five hundred and twenty times that by V squared now we need to get V squared by itself so the way in which we do that is divide both sides by two 5 200 so I'm going to do five hundred and twenty seven thousand six hundred and forty three divided by two thousand five hundred and twenty which gives me a value of 209 point three eight two dot equals b squared and then we just need to square root to make sure we just get a value for V so V equals fourteen point four six nine notice I have a rounded to early I'm now going to round to three sig fig so that becomes fourteen point five and it's a velocity which means the unit's meters per second so the meaty topic of conduction convection radiation this is all to do with thermal energy transfer so things heating up things cooling down starting with conduction now I'm sure you're aware that metals are good conductors the reason being is due to their delocalized electrons or you can say they're free electrons but delocalized sounds a bit fancier remember the structure of a metal you'll need to know this for both chemistry and the electricity topic of physics so to be honest it's worth learning so remember that a metal is made up of positive ions surrounded by a sea of delocalized electrons so what happens in the process of conduction is that when heat is applied the positive metal ions start by bracing and they gain kinetic energy what you find then is that the kinetic energy is transferred from the hot parts of the metal to the corner parts by the presence of these delocalized electrons so as the electrons move through the matter they carry the thermal energy with them vibrating the positive ions more and before long you can see how an entire metal object becomes hot now the opposite of a good conductor is an insulator and these are clearly going to be poor conductors so to point out things which are poor conductors first of all plastic and wood why because they have no delocalized electrons and that is the key point here air is also a poor conductor it is a good insulator and not just because it doesn't have any delocalized electrons but cleaning its ass so the particle is going to be extremely far apart so the chance of them vibrating and colliding with other particles to pass on the kinetic energy is going to be very slim hence why air is a good insulator so touching on some exams style questions so polystyrene why is it a poor conductor and that's because it contains at all air spaces and air is a good insulator because it has no delocalized electrons and the particles are very far apart so you want to link every single object you're given whether it's a poor conductor or insulator next up for example a duvet how does a duvet keep you warm it's full of feathers or synthetic material that looks a bit like cotton wool and the point is again that it traps air air is a good insulator it's a poor conductor so less heat transfer will take place meaning that you stay warmer so what we learn we have learnt that metal is a good conductor wood and plastic are poor conductors and that notice that solids will be better conductors than gases now convection is a very different type of heat energy transfer it only occurs in liquids and gases you cannot get convection in a solid and it makes no sense whatsoever and the key example we always use is a radiator in a house now my is wonderful drawing comes out so here's our rubbish radiator and it's nice and hot because it's got hot water flowing through it and what happens is that heat causes particles of air above the radiator here to gain kinetic energy now because they've gained kinetic energy the air expands which means that that the particles occupying more space now because they're occupying more space it means that they become less dense so they rise up to here as they rise they become cooler by definition they become denser and therefore they sink and before you know a convection current has been set up whereby the process keeps repeating and that's how a radiator in the corner of a room can actually heat up the entire room so we've got coffee in here and we don't want it to be getting cold too quickly so what can we do well I've already said you can put it in a polystyrene cup wipe to prevent conduction losses however because the coffee's hot can you imagine that bizarrely it will heat the air above the coffee and it will literally set up a mini convection current above the coffee that keeps repeating itself speeding up the process of cooling down that coffee so what you want to do here is add a lid and that's to prevent convection currents being set up the other great thing about adding the lid is you add a layer of air in here and remember air is a good insulator so you're preventing heat losses by both convection and conduction by adding a lid last hour radiation infrared radiation which we will have met in the electromagnetic spectrum it is a wave which means it is not dictated to by the state of matter what I'm trying to say here is that it can travel in solids and liquids and gases and that kind of automatically makes it the most difficult to try and prevent heat losses via however there are certain things you can do and that's all to do with the color of objects so do try to remember that white shiny surfaces reflect infrared radiation which is why in very hot countries like certain parts of Spain you might see the houses a white same in same was true for Greece and that's because the white colour reflects infrared radiation anyone with dark hair black hair you'll notice that your head gets really hot in the Sun why because black matte objects are very good absorbers of infrared radiation and notice that the hot of the object or the grace of the difference between the object and the surrounding temperature the greater the rate at which heat is lost but in this more into contact said looking at a thermos flask am I even going to try and draw this oh God okay so that's appalling you John but I can still point out a few things so first of all the most obvious thing here to point out is that it has a vacuum now remember that a vacuum is a space with no particles and we know that both conduction and convection require particles in order to occur so we say that there is no conduction or convection that can occur within this vacuum and as always unlinking the property with which type of heat transfer it prevents there are silvered surfaces which line the bottle or line the flask and the point of that is that it reflects infrared radiation back at the contents of the fast keeping it hot or keeping it cold the lid prevents convection currents which I've already touched upon and you can say that the whole thing is made out of plastic because plastic is a good insulator and that's the way you get these answers nice and scientific is by pointing on the various parts of it and what it stops so looking at heat transfers within a home how can we stop all our heat escaping so first of all in the loft you can have loft insulation which contains lots of air spaces air is a good insulator preventing conduction heat losses you could talk about the cavity walls so cavity meaning a hole like a cavity in your teeth so there's holes within the walls which contain air again because air is a good insulator do you notice though that convection currents can still be set up in air which is why you often find there's also foam because that solid foam stops the convection currents being set up you could talk about the radiators now having a silvered surface and that's to reflect infrared radiation back at the room and lastly double glazing remember that's when you have two window panes which trap air between them helping to prevent conduction question 9 the diagram shows how an waves near the coast on a warm day explain why our me man moves explain why air moves are shown on the diagram hopefully the fact that there are arrows and we're talking about a gas which is air and heat hopefully that's screaming convection at you so again this is a pupper answer you need to learn your convection answer so first of all state that energy is transferred from the Sun which heats the land this means that above the warm land becomes warmer so the particles gain kinetic energy and effectively the air expands and becomes less dense this means that that heated air rises and therefore there's a space so cooler denser air falls in order to replace that warm air and you've therefore created a convection current which repeats so this is a convection current answer which you need to have just learn off by heart although they have given you a different scenario to the usual radiator in a hot room so try and make it applicable to the questions so let's start by looking at the warm land initially the warm land heats the air and that means that the air has gained kinetic energy so the air expands becomes less dense and rises so as that warm air moves over the sea it becomes cooler and therefore denser so that cooler denser air Falls and replaces that air that was above the warm land and then by doing so you've created a convection current which keeps repeating itself explain how brainian motion provides evidence that air is made of small particles so remember of Rayleigh emission our example here of pollen grains in water or smoke particles and remember that these large particles will move with random motion and they collide with smaller invisible particles and that's the particles which we find in a so we're looking now at the density and pressure topic so remember density is to do with how close together particles are heavy objects have high density and that's because the particles are close together lighter objects are less dense and that's due to the further apart spacing of the particles in an equation you need to know about is density equals mass over volume now I use a formula triangle as usual to remember this and one of my tutees taught me a good way to know this is drunk men vomit so you want D at the bottom of the triangle and at the top V at the bottom so to work out density it's the mass over volume mass is density times volume and volume is mass divided by density they're quite interested in you being able to determine the density of various objects so let's start with symmetrical objects things that we can easily measure the volume of so things like cubes cuboids brick for example now what you want to do here is obviously looking at the equation density because mass over volume you want to measure the object's mass using a top pound balance and get that measurement in kilograms then to measure the volume we simply use a ruler we measure the length width and height multiply those values together to work out the volume substituting your mass and volume values into the equation and out pops the density now it's going to be far more difficult measuring the density of an asymmetric object something like an ornament or avars or a stone and that's because you can't easily measure the length width and height of the objects so it's very difficult to determine its volume this time we're going to use the displacement method the simplest way to describe this is you fill a measuring cylinder with water you measure the volume then you add the object to that measuring cylinder and you measure the new volume and the difference between those two values will clearly be the volume of the object so it's volume is now sorted its mass is easy to determine using the top and balance method substitute the values into the equation so make sure you state the equation in your answer that would be worth a mark and out pops density now pressure so pressure is acting all around us remember the press Brown atmospheric level is a hundred thousand Pascal's or 100 kPa and the pressure increases underwater and if anyone goes scuba diving you'll notice when you have to do your training you need to be aware of the pressure around you and the reason the pressure and create increases is simply because there's more water above you that must fear above that and it's all bearing down on you hence you experience a higher pressure at the top mountains you'll have less pressure and not simply because there's less air above you now in terms of when you go up in an hour painters to try and give you some context is anyone ever notice that you get bread rolls and those little plastic packets or packet of crisps and it looks like a pillow in an aeroplane you get super puffy and that's because when the packet crisper example was sealed at ground level then you have the upside pressure around so that gets sealed into the packet and so you've got those particles collide increasing pressure against the walls of those crisp packets however when you go into an airplane and you're at altitude and what you find is the surrounding air there's less pressure so you find there's more pressure within the crisp packet less pressure surrounding it which is why it puffs out and you need to have to describe what pressure is in terms of particles so taking particles within a crisp packet or within a container within a square tea cream container just remember that those air particles collide with the walls of the container no what are you doing Lara no no claws no claws no no together this is be good be good she always me out and I talk to her as you know she's been naughty like oh so those particles collide with the walls of the container creating a small force and that force given over a specific area is the pressure and we know this because of the equation pressure equals force over area so you can use the triangle FAPE to help you remember that do you be prepared to provide answers to what pressure is or how the pressure is produced within a container as that could be worth 4 marks I do remember those particles within the container have random movement because they are air particles and they are gas why did that pressure increase with increased temperature well clearly increased temperature provides those particles with greater kinetic energy which means they collide with the walls of the container both more frequently and with greater force hence you see an increase in the pressure so if we go the opposite where we decrease the temperature clearly the decrease in the temperature will decrease the kinetic energy eventually the particles will have no kinetic energy whatsoever and at this point we say that Absolute Zero has been reached because particles have no kinetic energy there is no pressure it has a value which is minus 273 degrees Celsius and if we're using the Calvin cycle which is a different scale for measuring temperature so we we are used to dealing with Celsius however the Kelvin is also a very good system and we say that absolute zero is zero Kelvin so be able to come up between the two scales so minus 270 two degrees Celsius is zero Kelvin so in order to combat between the two to get from Kelvin to degrees Celsius you want to add 273 and to get from degree Celsius to Kelvin you want to minus 273 so let's take an example 20 degrees Celsius what is that in Kelvin it is 293 Kelvin because we've added 273 here I'm looking at a question so which exerts more pressure on the ground at anchor the weight of 8,000 Newtons or cyclists for the weight of 1000 Newton the tank trucks have a contact area 10 meters squared and each of the cyclos tires have a contact area of not pointing up six meters furred so what you need to do is begin by drawing the triangle to help you sort out your formula so it looks like this forces at the top and it is area and then it goes pressure so I'm going to change it to black so I'm obviously looking at the pressure so I need the form of the equation which looks like this force over area I'm going to start by looking at the tank so it's pressure will be its force and obviously that will be the 8,000 Newtons why because weight and force have the same units so that is Newtons and therefore we can use them interchangeably so that's 80,000 divided by the area which I've been told is 10 and here's the answer answer 8,000 Newtons per meter squared now let's look at the cyclist okay so the pressure will equal the force again which is this time a thousand Newton's divided by the area now don't make a mistake here the area is to lots of naught point naught naught six the reason being because obviously the cyclist has two tires so I'm gonna do not point naught six times two equals 1,000 please don't let me run out of space by a naught point naught one two I'm going to use the calculator here and the answer here is eight three three Newton's meters squared so as you can see it's obvious that the cyclist exerts more pressure because their pressure is 80 2333 to make sure you write that the cyclist is the answer question for a diver works in the sea on a day when the atmospheric pressure is 101 kiloPascals and the density of the sea water is 1028 kg per and the driver uses compressed air to breathe underwater 1,700 liters of air from the atmosphere is compressed into a 12 liter gas cylinder the compressed air quickly calls to its original temperature calculate the pressure of the air in the cylinder the only reason these questions are hard is because you need to actually pull out the information and the question once you've done that it's straightforward enough so what numbers have we been given well we've been given atmospheric pressure of 101 kPa density which is here but I don't think we need to use that quite yet we've been told that 1700 liters of air is compressed into a 12 liter gas and so we can see here straight away we've got two volumes we've got a pressure and we've got another pressure so which equation contains two lots of volumes and two lots of pressures well it's this one correct me if I'm wrong but I think this is given on the front of your paper but it's quite straightforward to remember anyway just make sure your units are all the same and then start subbing in these numbers so pressure one is going to be a hundred and one times volume one which is one thousand seven hundred equals we're looking for p2 so I'll keep that there times 12 and then the way to work this out is work out the left hand side first of all so 101 times 1700 and then divide both sides by 12 and then when you round that to three sig fig you're going to get p2 equals one four three zero zero the units will be killer Pascal's state the equation linking pressure difference data density and G so you can write this out in words you can literally write pressure difference equals depth times density times G or you can write it out as symbols which would be P equals H times remember it's the Greek letter Rho which looks like a piece that's why it's a bit confusing times G so if in doubt I would write it out in words whatever you do don't write gravity for G they're very fussy over this you need to write acceleration due to gravity calculate the increase in pressure when the diver descends from the surface to a depth of 11 meters so what you're going to do here I'm just going to write out the equation so pressure equals height times density Rho times G so 11 time density which we were given like the beginning of the question which is 1028 times G which is 10 and we need to know that number you can use 9.8 also but 10 is easy and then you write that out and you get an answer which is a hundred and ten kPa part three calculate the total pressure on the diver at depths of 11 meters assume that the atmospheric pressure remains 101 kPa well because it's worth only Walmart they've only given you a small gap you shouldn't be doing any proper calculations here so no substituting into equations you simply need to add together your previous value to the atmospheric pressure so that's 101 plus 110 which equals 211 kilo Pascal's see as the diver breathes out bubbles of gas over lease term rise to the surface the bubbles increase in volume as they rise explain this increase in volume two months make two separate points one of the most basic arguments you can make here is that'll be warmer closer to the surface of the sea because you're closer to the Sun that would be worth 1 mark and what that does because remember if it's warmer the particles vibrate more and therefore the pressure will increase inside the bubble which needs to its volume increasing or you could give an argument to do with the fact that pressure decreases closer to the surface always provide an equator in this case that would be pressure equals height times density times G and then you would state that the PV value is constant for a fixed mass of gas and if that sounds weird you can state the other pressure equation once again which is p1 times v1 equals p2 times v2 the diagram shows some gas particles in a container the piston can be moved in or out to change the volume of the gas add hours to the diagram to show the random motion of the gas particles just literally show them just moving around really randomly just make sure you add enough arrows that just a gas so it's quite straightforward explain how the motion of the gas particles produces the pressure inside the container this is an answer you can write learn so you want to first of all talk about the fact that gas particles have random motion and that they collide with the walls of the container then this creates a force and then lastly States an equation which is pressure equals force over area and that is the easiest way in which you'll get three marks I would really recommend you learn the ants off by heart state what would happen to the pressure if you push the piston into the container without changing the temperature well you've got a smaller volume so therefore the pressure would increase when the gas in the container is heated the piston moves outwards place ticks against the three correct statements the gas particles get bigger no that's not true the mass of gas particles stays the same yeah that makes sense the gas particles move faster more clearly if you heat them they're going to gain kinetic energy so they will move faster the average distance between the gas particles increases again true because if they're moving faster they'll be moving away from each other therefore increasing the distance the temperature of the gas decreases will know the containers been heated so that's actually absolute rubbish I'm going to show you some more density questions because I've touched on this density triangle which I told you is drunk from any vomit here but there's another equation you need to be aware of with density which I'm going to bring up now because I found at this particular example so I could talk about it so question six this about pressure in a liquid the teacher uses this operators to demonstrate pressure difference in water the apparatus is hollow and has three short tubes are different apps the teacher completely fills the apparatus with water and water comes out of all the tubes so look part of the water from the top of the tube state the relationship between pressure difference height density and G so I wouldn't use a triangle here you do just need to learn this and it is pressure difference equals height times density times G that does not look like a G don't know I can't do it that times properly the diagram shows the path of water coming from the top tube complete the diagram by joining the pass of water you would expect to see from the other tubes now notice that this question exists I have a lot of people I teach the probably wouldn't even have spotted that that was a question I would have lost two months immediately so do make sure you read every single question and then you indeed attempt every question now I already told you that the lower down you go in water so the farther onto the ocean the same is the case here the greater the pressure that is experience that means that the path of water coming out the lowest pipe will have traveled the furthest you to that increased pressure so we're looking at something like this and then for the middle tube we're looking for an intermediate pass so like that explain the pattern of the pass of water from the tube so I've accidentally already alluded to this you want to say that the water at the bottom of the tube has greater pressure and therefore the force acting on it is the greatest meaning that it travels furthest in another demonstration of the teacher uses this container the containers made of glass each section has a different shape the teacher pours water on to the container until it reaches the level shown in the left-hand section complete the diagram by drawing the water levels in the other four sections so if we this is probably quite a hard question so just be aware that the air pressure is the same for all visors after all they are connected and that means that the water level will be the same for each regardless of the shape make sure you actually draw within the bars I have a habit of drawing outside of the bars so I'm going to use in the exam a ruler to show is constant for each vessel explain why the water fills the container in the way you have shown so we need to describe why we've drawn it at that constant level well I've already said that the air pressure is the same for all so that's worth one mark we know that its water we know we haven't changed liquids throughout therefore the density of the liquid will remain the same and then look at how that equation links so pressure difference equals height times density times G gravity hasn't changed density hasn't changed pressure hasn't changed therefore height won't change hence the same height for each and lastly you could point out that the vessels are connected so magnetism well we're going to start by first of all stating which metals are magnetic that is iron steel cobalt and nickel and the two most common examples we'll come across that obviously iron and steel do notice that steel is an alloy of iron which means that it contains iron but it also contains the element carbon a few basics to point out which is if you have a bar magnet or any magnet remember that two North Pole's will repel so if you try and push them together the slide past each other the same is true with South Poles they'll repel as well and that opposites attract so a North Pole will attract a South Pole looking at the difference between a soft magnetic material and a hard magnetic material now the real difference is that a hard magnetic material maintains its magnetism so steel for example is a hard magnetic material it does not lose its magnetism easily whereas iron loses it very easily and to put this into context if we use a scrap metal yard as our example here scrap metal yards are full of big old lumps of iron which needs moving around now you actually use a magnet to move them around and what you do is you turn on the massive iron electromagnet and it becomes magnetized it plumps down and picks up that metal that it's trying to move and then when you've moved it across to the new position you can basically cut the power source and it will lose its magnetism you couldn't use steel in this case because you did effectively find that all that scrap metal would remain stuck to the magnet and you'd never be able to pull it off so what is a magnetic field line well it's the space around a magnet whereby magnetism can be detected and in terms of designing experiments whereby you can determine the shape of magnetic field lines you have two options here first of all iron filings and secondly using plotting compasses so what you do is to get a piece of paper you sprinkle or iron filings onto it and then you place a bar magnet underneath and you'll see that those iron filings are lying themselves with the magnetic field with a plotting compass instead you place your bar magnet on a piece of paper you place their plotting compass near and you make a note of the direction in which the arrow on the plotting compass is pointing and then you pick it up put it in a new position keep repeating that process and who you've drawn the magnetic field lines you now just remember that a solenoid is a cylindrical coil of wire touching now on the right hand grip rule so this is just a way of showing the direction of magnetic field lines so my thumb represents a wire so in this case it's going from north to south or from up to down and you might be asked to draw the magnetic field line directions and just follow the direction in which your fingers are pointing be aware of a uniform magnetic field and all you'll see here is that the lines the magnetic field lines are evenly spaced and that they're parallel and there's the two points you need to point out with a uniform magnetic field so how can an object's Magnus's and being juice so how can it become magnetic well first of all you need to start with a magnetic metals such as iron and steel and then you can place it inside the magnetic field of a permanent magnet and it's magnetism will be created or induced obviously the moment you remove that object the iron object from that magnetic field it will lose its magnetism still I've already pointed out is a hard one netting material so it will tend to retain its magnetism so how is a simple electromagnet constructed and that's simply by connecting a wire to a circuit and running a current through it how can we increase the strength of the magnetic field of that wire carrying a current well the most basic thing we can do is obviously increase the current and we can also wrap the wire into a solenoid so if we coil it up that will also increase its magnetic field strength we're now interested in increasing the magnetic field of a solenoid because it's already in a coil what you can do now is add more turns of coil or you could add an iron ore which is just like an iron bar which you thread through the middle of the solenoid you can also increase the current as I've already specified we're now looking at the motor effect which is the part of this topic which people really aren't a fan of but if I talk you through the overview first of all and then we'll look a bit more closely about how it all works so let's start by looking and what the motor to effectuate is a normal motor effect is know their motors a piece of wire that spins so that's what's happening in a motor a wire is spinning and we're trying to work out how we can create that and that is why the motor effect and you might have seen a simple motor being built at school so what you have here is you have two permanent magnets you have a wire in between them which is coiled up and then that is attached to an electrical circuit so it can carry a current and the point here is that when the wire carrying account is placed within this magnetic field of the two permanent bar magnets you find that there's a phenomenon which we call the motor effect and what will happen is that wire will start spinning and you have a simple motor that's only if you've got a coil of wire placed within the magnetic field or two permanent magnets and it needs to carry a current and you've probably heard of Fleming's left hand rule and that's what I'm going to talk about now and that's just a way of working out whether the coil moves up on one side or whether it moves down because obviously has to move up to begin its spin then it moves down moves up and moves down so that's what's happening with our motor so looking at Plemons left hand rule you've got to hold your thumb forefinger and second finger at right angles to each other now the thumb represents the force for the motion and that will show the direction in which one side of that coil will be moving so taking a left-hand side for example in this instance it would be moving upwards the first finger magnetic feet the first finger shows the direction of the magnetic field I remember that the magnetic field always runs from north to south so based on that diagram you get given in the example in your textbook have a look at those two permanent bar magnets look at the North Pole look at the South Pole and make sure that your first finger matches up with that your second finger shows the direction of the current and on your textbook it should show an arrow showing which way the currents running if it's running clockwise or anti-clockwise just make sure that that finger is lined up that so once you've lined up your magnetic field which is your first finger your current which is your second finger you'll find that your thumb even points up or it points down and so it will ask you which direction will the coil move and you will say upwards or you will say downwards just make sure you've got them all in 90 degree planes to each other my way of remembering what finger stands for what is that the first finger is your magnetic field first field second it contains a seeing means that it is showing you the direction of the current so in terms of answering the five markers which tend to be something like a wire is placed within the magnetic field and a force is felt discuss it's worth five marks so it doesn't matter how they word up these questions answer is always the same you want to start by saying the wire carrying the current so your coil has 8 ampere magnetic field and what that does is indigent and it interacts with the permanent magnetic field of the bar magnets this creates a force causing the wire to turn and believe it or not this applies as well when you're talking about a large speaker because anything that moves in and out in this way involving magnets will use the motor effect even though it doesn't seem particularly obvious so taking the speaker cone for example we start by saying that the wire carrying the car has a temporary magnetic field this interacts with the permanent magnetic field of the bar magnets found in the speaker this creates a force and this force moves the speaker cone upwards vibrating air particles causing the sound that reaches your ears so you're using the same answer here and honestly as long as there's a wire moving or the speaker cone moving your answer remains the same the photograph shows a small electric motor explain why the coil starts to spin when the switch is closed remember this is a magnetism question so this is an answer which you can definitely wrote learn so what you want to say is when the switch is closed that the current flows around the circuit this creates a temporary magnetic field around the magnet which you can see is near the coil it's it's stuck in the coil so right here is where the magnet is so this temporary magnetic field interacts with the permanent magnetic field of the magnet which creates a force and that force is what is used to turn the coil and you can mention Fleming's left hand rule just for an extra mark so just how to make the coarse spin in the opposite direction the obvious thing here is to switch the direction of the current or you could have swapped the magnets over so just how to make the coil spin more slowly so how do we weaken that magnetic field well we can reduce the current you could also produce the voltage or had a weaker magnetic field which is harder to quantify 3a state what is meant by the term magnetic field line and that's the line that shows the direction of the magnetic field that eigem shows the cross-section through a wire placed between two magnetic poles and the wire cows that actually come into the page at X the shape of the magnetic field is shown add arrows to any two lines to show the direction of the magnetic field now remember that it runs from north to south and we have to do that on at least two lines so I've done two there draw an owl on the diagram to show the direction of the force on the wire and label this F so this is where Fleming's left hand rule comes in so remember that your thumb shows the direction of the force your index finger shows the direction of the magnetic field and you'll see and finger shows the current so make sure you you're holding your left hand up here make sure that your second finger is pointing downwards at X then line it up so that your first finger is pointing north to south and then when you've done this you'll see that your thumb is pointing to the right and remember that shows the force which is why it's in this direction now we need to describe the magnetic field in the region shown inside the dotted square so if you have a look at that you can see that first of all the magnetic field is in uniform because there the lines are different spaces apart and also notice that they're flowing in the same direction so they are parallel to each other now we're gonna look at electromagnetic induction or basically how voltage or current may be induced it's a very similar concept we just need to look at it from a slightly different angle so I hope you realize that with your force and your magnetic field in your current it's a bit like a physics formula triangle which is that if you put in a magnetic field and you put in current then you get force so it makes sense therefore that if you put in the force you put in the magnetic field then you should be able to make current and indeed that's what electromagnetic induction is all about if a wire is moved into a magnetic field at right angles then you find that a voltage will be induced and if it's connected up to a complete circuit that's where your current comes from do you notice that you must move the wire all the magnets it doesn't matter which way around you do it you must move them at 90 degrees to each other if they're parallel then you won't induce your voltage now in terms of working out which direction everything is going to move in this time you use Fleming's right-hand rule so you find again that the thumb shows the direction of the force or the motion first thing is the magnetic field second finger is the current but you have to use your right hand because otherwise it won't line up properly if you use your left hand and this is really how a simple generator works because if you're creating current then clearly you could make electricity from that and all the generator is is a machine which creates electricity so how could you increase the size of that induced current or clearly you could use stronger magnets you could use to have a stronger magnetic field you could move the wire more quickly and you can backed away into a coil looking at the use of generators in everyday life you can use the example of a bicycle dynamo and just to explain what this is so some bikes they don't if you've ever used the Boris bikes in London or any of those bikes you can rent in other countries do it if you've ever cycled them in the night but they have lights and it's not because they have batteries that need replacing it's because they contain simple dynamos which uses your motion or pedaling the bike to actually power the lights so you need to explain from an electromagnet point of view how that works so as you turn your pedals clearly the bicycle wheel turns this turns a magnet which is located within a coil and this magnetic field of the magnet cuts the surrounding coil which induces a current so within a bicycle dynamo you find that there is indeed a simple generator also be aware of the involves of the relay switch and the circuit breaker and an electric doorbell do notice that with these sorts of questions it's most likely they'll give you a diagram and it's just up to you to describe what is happening so always start with the switch when you're talking about the door bar so you press the switch causing a current to flow the current flows to the electromagnet causing it's become magnetized and the designs of these bolts will vary a fair amount but they're fundamentally the same there'll be an iron rod or an iron armature which will be attracted and because of the way it's pivoted it means that it's attached to a valve that hits argon and that's how the doorbell sounds so just make sure you look at the diagram you're given and follow those steps around starting from the switch being pressed it and you will get your marks do you notice that relay switch is effectively a safety device it's used to turn on very large currents so what you find is you press the switch to complete the circuit and it will be attached to a different circuit which contains a much larger voltage and it's the safety device because you don't want a person touching the switch attached to the very high voltage supply such as 1 million volts because if there's a fault it could easily kill them you could electrocute them and this is seen in things like flood lights at stadiums there can be millions of volts going through those huge lights you don't know person in danger so that's where relay switch may be used and you can also find it in car engines you turn your key that will be involved in a relay switch which will be involved in turning on the car engine with the circuit breaker this is a safety device used in houses so it's when the comment becomes dangerously high you find that the electromagnet becomes magnetized pulling away part of the circuit meaning that the circuit is no longer complete and therefore you cut off the supply in electricity love meth users they work in a similar way they're both safety devices however you will find that a circuit breaker is preferred because it responds far more quickly and it's much easier to reset because you simply press a button we start by looking back in history and look at the original structure of the atoms so we can actually understand all our findings that we know to be true today so originally there was the Thomson plum pudding model now you don't need to know too much about this but just know that a plum pudding this was in the 1800 by the way so you can imagine a Christmas pudding if you don't know what a plum pudding is I don't know one what is so big sphere of sponge embedded with different types of fruit and in the case of the plum pudding those were plums and Thompson stated that the sponge was made out of positive charge and that those plums embedded within that sphere of sponge were the electrons now we know that this is false because we now know the modern-day structure of the atom with its nucleus and its shells with the electrons suckling and we're going to talk about the gold foil experiment to help us understand why this new item became the accepted model so Rutherford fired alpha particles and we'll talk about alpha particles soon at gold foil now he found that most of them passed straight through and this was strange because really if the atom was structured like a plum pudding there's no way these alpha particles should have passed straight through but because they pass straight through it told him that the atom is largely empty space which we know to be true some alpha particles would deflect it and because an alpha particle is positive he had told him that they had to hit something also positive and that they had been repelled and that made him understand that the nucleus was positively charged which we know to be true because that's where the protons are found lastly very few of the alpha particles were deflected in this way and this told him that the nucleus was very small so do link together what he did with what findings he found out and the conclusions he drew from those findings and I'll help you score really highly so we now have our structure of the atom we know that it has a nucleus containing protons and neutrons remember this is also known as the nucleon number and that's just the name given to all the particles found within the nucleus and surrounding the nucleus are the shells of electrons where the electrons orbit so just to remind ourselves that the mass of a neutron and approach it's one a mass of an electron is very small so 1/2 thousand or 1800 depends where your teachers taught you and that the neutrons because they're neutral have no charge protons have a positive one charge and electrons have a negative one charge now looking the periodic table just remember that the atomic number is the number of protons and the neutron and the mass number is the number of protons plus the number of neutrons and this has become really important when we now come to look at isotopes you've probably met isotopes in chemistry so things like carbon-12 carbon-14 remember that these are atoms of the same element with the same number of protons but different number of neutrons if we look at carbon-12 and carbon-14 in the periodic table they both have an atomic number of six which makes sense because they're the same element which means that they must have the same atomic number then mass numbers are different no carbon-14 has two extra neutrons when compared with carbon-12 so when we look at radioactive isotopes we're just talking about isotopes which are unstable and tend to give off radiation so ionizing radiation may be given off an atom and this is a random process and it may give off alpha beats or gamma radiation and that's what we need to talk about now so I'm going to start by chatting you will opt out four beats and gamma radiation is and then I'll show you some decay equations so alpha radiation first of all so what happens when alpha radiation happens is that two protons and two neutrons are lost from a particular atom and clearly therefore you will have a new element whose atomic number remember that's the proton number is to fewer than it was before and the mass number because it's lost two protons and two neutrons will have gone down by four with beta radiation what's happened this time is that a neutron has turned into a proton and stayed within the nucleus of that particular atom so because a neutral and a proton has the same charge clearly the mass number will be unchanged for the proton number will have gone up by one so you will have a new element now gamma radiation very different because it's an electromagnetic wave so you see no change in mass or atomic number do you notice that alpha radiation is the largest it has the largest mass because it's made up of two protons and two neutrons and it is the most ionizing whereas gamma is the least ionizing an ionizing leech is the ability to cause something else to become an ion which is a charged particle so if we compare the properties of alpha beta and gamma notice that alpha as I've already said it's the most amazing beauty is in the middle gamma is the least ionizing in terms of their penetrating powers that's how easily they passed through substances you notice that alpha is stopped by a has stopped for aluminium foil and gamma is stopped by several centimeters of lead or several meters of concrete in terms of their range in air alpha has a range of only about five to ten centimeters besa has a few meters range whereas gamma has an indefinite infinite range in air the table shows the nature of alpha beta particles so alpha we know is a helium nucleus made up of two protons and two neutrons and b2 is a fast-moving electron you explain why alpha particles and beta particles have different penetrating powers so basically let's start by looking at the difference so state first of all that alphas are much larger because they're made up of two protons and two neutrons so they have a heavier mass they have a higher charge this means that they cause more ionization which means they can't penetrate as far and that's due to all energy which has been lost as they've caused lots of ionization and also point out that the alpha particles are more likely to collide with the atoms because they are bigger or you could give the converse argument for beta so you could say they're smaller they have less charge they cause less ionization they have a lower mass so in this first alpha decay equation let's have a look we need to work out the new mass number and the new atomic number of thorium so we're starting with uranium-238 that is its mass number well I've just told you that you lose two protons and two neutrons in alpha decay which means the net mass number must have therefore decreased by four which is why it's new must is two three four because you've lost two protons it means that the atomic number decreases by two to ninety and that is your answer in the second example I'm after the new mass number of lead so we've lost two protons two neutrons again which is why the mass number will have decreased by four to become to one two and this time we're looking for the original atomic number or proton number of polonium so we know that we've lost two protons to get to 82 which means the original atomic number must have been to more than 82 so the answer here is 84 in this b2 equation we're looking at what happens to sodium so I've already told you that in beta decay a neutron turns into a proton and stays within the nucleus of an atom because of that the mass number is unchanged so we're going to stay having a mass number of 22 the neutron turns into a proton and stays within the nucleus and because of that we have an increase of 1 on the atomic number so that turns into 12 and because we've increased our Tomic number we clearly have a new element and if you look in the periodic table you'll see that the element with the atomic number of 12 is neon so in this question we're looking for the new mass number in a new proton number again so we have a neutron turning into proton meaning that the mass number is unchanged which is why I'm going to write a 14 here because we've gained an extra proton it means the atomic number will have gone up by one forming seven and because you have a new atomic number we have a new element and that element of according to the periodic table is nitrogen now we're going to be moving on to looking at half-life and background radiation so let's first of all state what is background radiation and it is radiation which is always present in our surroundings and so you may need to list several sources so that could be cosmic rays from space it could be radioactive rocks like granite found in Cornwall could be food and drink and medical sources such as x-rays now what is the unit for measuring radiation it is the Becca L capital B little Q and what instruments to be used to measure the level of radiation whether that's background or not we use the Geiger Miller detector or counter do you remember if you're given a radioactive source and you need to determine its radioactivity you must work out the level of background radiation and then to and then subtract that from the value you get from your Geiger melih counter to make sure that you remove it from your calculations so half-life now let's define it first of all remember this is the time taken for half the radioactive nuclei to decay and you might have used coin tossing at school to help you model this the reason why that works really well is because radioactive decay is a random process and as is tossing the coin and with tossing coins you've no idea you can't predict where they will land on heads or tails and it's the same with radioactive decay you have no idea which of the radioactive atoms will decay first in terms of using tossing a coin as a model does have several limitations and this is really the number of times you can do it I mean realistically probably at most about thousand times whereas with radioactive decay you're looking at millions of atoms which need to decay and now I'm going to show you a question involving half-life and I'll talk you through the half-light calculations because they're probably the most difficult part of this topic a sample of sodium 24 has an activity or fourteen hundred becquerels on the access sketch a graph to show how the activity of this sample changes over the next 40 hours the half-life of sodium 24 is 15 hours so at time equals zero we're going to have an activity which is 1,400 we know that the half-life is 15 hours so look along 15 hours half for 1,400 is 700 so we need across there when another 15 ours has taken place so at 30 hours that's 700 will have hard again for 350 so we need a mark here and now you can attempt to draw a curved line which I'm appalling up oh it's not too bad granite is a rock it contains a radioactive isotope of uranium that decays very slowly explain how scientists can use this radioactivity to find the edge of a piece of granite so first of all make a note that there is a known proportion of activity when the rocks are formed this means that you can now measure the proportion of uranium now and then you compare the activity of the original uranium value with the activity now and this can help you determine the number of half-lives to which have elapsed and then you calculate the age from reference to half-life so Jess why the age of a piece of granite could not be fine using uranium isotope with a half-life for 15 hours and that's obvious because the half-life is too short 15 hours as meant that the decay has occurred far too quickly and so the activity now would be far too small to measure even 25 has a half-life of 1 minute what fraction of it remains after 3 minutes so what you have to do here is work out how many laughs half-life's have occurred and because it's 3 minutes and one goes into three minutes three times three half-lives they've occurred and then all you have to do because you're finding out a fraction is do 1/2 times 1/2 times 1/2 to find that 1/8 remains after 3 minutes question 3 then on 1 3 3 is a radioactive gas use for diagnosing lung problems in 15 days it's activity falls to 1/8 of its original value what is its half-life so we need to work out how many half-lives occurred to get to 1/8 so what you need to do is you might have to do trial and error but you need to just do as many half-lives as you need to in order to get to 1/8 and the answers actually going to be three of them so three half-lives occurred in 15 days so how long did it take for one half-life to occur where you just need to do 15 divided by 3 and answer is five so five days is its half-life question for the half-life the radioactive isotopes alien 24 is 15 hours a sample has a camera to a to 240 counts per minute this can't wait 60 hours later we'll be okay so this time again we need to find out how many half-life's I've occurred so I'm going to do 60 hours divided by 15 and I see that four half-lives have occurred so therefore after one half-life 120 counts would remain but there were four of them so I'm going to times it by a half four times and that is the same as 240 times answer and that is 15 as my answer so it's count me after four half-life's have occurred so I divided 240 by 2 or times them by half 4 times and I have got 15 as my answer so that's 15 counts per minute question 5 a radioactive isotope of silver has a half-life of 20 minutes a sample gives a rate of 6400 counts for a second at 9 o'clock what time will decant maybe about two hundred counts per second okay this sounds hard but again just use trial and error to work out how many half-lives have occurred so I'm just gonna gee 6400 times 1/2 and I've got 3,200 so I'm going to times it by half again and I'm gonna keep going until I get to 200 and actually what I found here is that it has taken five half-lives in order to get to 200 counts so all I did was times 6400 by 1/2 five times and I got to 200 so like I said that means five half-lives have occurred and each half-life took 20 minutes so therefore five half-lives takes a hundred minutes so all you need to do now is work out what 100 minutes past 9 o'clock is and remember there 60 minutes an hour so that brings us up to 10:40 that one was quite hard but you can work it out like I said just use trial and error to work out how many half-lives have occurred practicing as many questions that these as possible in order to get good at answering the different types of question remember when you're reading off graphs to look at you can beat off the half-life by looking at how long it took for the counts to reduce by half and then you need to read a cross to see how long that took take into account background radiation because you'll see that the graph line will never actually touch the x-axis and that's because background radiation exists and remember but that comes from things like cosmic rays x-rays rocks just general stuff really and remember half-life is actually the amount of time taken for half the radioactive nuclei to decay so after 42 days the activity of a sample of phosphorus-32 has decreased from four hundred becquerels to fifty backwards what is the half-life of phosphorus-32 so we've gone from having an activity of four hundred becquerels to fifty so we need to work out how many half-lives took place so there's the first one which would have taken us down to two hundred becquerels the second one would have taken us down to one hundred becquerels and then the third one would have taken us 250 back around so we can see here that three half-lives have taken place and what was our time frame well three half-lives must have occurred in 42 days so then it's a simple expedient of June 42 divided by three to work at how long each half-life took and that answer is there for 14 days looking at uses of radiation alpha radiation is used in smoke alarms I'm going to chat see how this works so you have an alpha source in a smoke alarm which is giving off alpha particles and what happens is those upper particles collide with particles in the air and they ionize them creating a small electric current which is picked up by the detector now I've already told you that alphas range in air is very limited so the moment there's a fire there's now smoke particles in the air and they obstruct the Alpha and they stop it reaching the detector so they're detected get zero reading and therefore the alarm goes off Beauty radiation is used in aluminium foil thickness to kitchen for the eruption sandwiches in so there were two bowlers and there's a detector either side so you've got a source of beta detector on the other side and there's a certain amount that should be picked up and if that detector reading is too low it tells you that the aluminium foil is too thick so the rollers pressed together to make the foil thinner and so the detector can pick up the correct amount in terms of been used in medicine do you remember that we used radioactive sources in medicine such as radioactive iodine and we call this a medical tracer and that's because it's used to diagnose things like kidney problems so the patient takes a sample of radioactive iodine it flows through their body and as a detector which picks up how much radiation there is and you'll see a characteristic graph meaning where the reading stays high and that tells you that there's a blockage within the kidney so they do make great diagnostic tools do notice some crucial properties there and that is that you've got to have a an isotope which decays into a stable product which makes sense because you don't want it giving off radiation it has a medium-sized half-life you don't want it to have such a short half-life that you can't actually pick up how much there is because it's already decayed away but you also don't want it to be so long that you're staying radioactive for many years to come because that is dangerous and this is because of all the dangers relating to radiation to remember ionizing radiation causes mutation within ourselves a mutation is the first step leading towards cancer so it's pretty nasty stuff we can reduce our risk and limit our exposure to radiation by wearing protective clothing by standing behind LED shields by using tongs to handle the radioactive material and for using things like photographic film you see these internal medical badges that radiographers wear and that will show up if they've been exposed to too much radiation looking at use of radioactive carbon - carbon 14 in carbon dating so that's when you determine how old plant material is for example so carbon-14 is radioactive and during a plant's lifetime remember when it photosynthesizes it takes in carbon dioxide so a certain proportion of the plant will contain carbon 14 now once it dies clearly it won't be photosynthesizing anymore and over time that radioactivity decreases and by comparing the radioactivity of a sample with the radioactivity of a living version of that particular plant you can work out how old it is that's a very clever dating technique so nuclear fishin let's be very specific with our definition remember that it is the splitting of an atomic nuclei do say atomic nuclear if you don't say that you don't get the mark so where is this carried out its carry out artificially within a nuclear reactor which means we need to add a fuel and we tend to use uranium-235 so we have our nuclear reactor which contains uranium-235 to get the nuclear fission process underway we have to fire a single Neutron at that uranium nuclei the uranium nuclei splits into two daughter nuclei and I'm being very specific with my wording and you should be using this exact wording in your exams releasing 3 2 to 3 neutrons these go off and collide with other uranium nuclei which splits forming two more daughter nuclei and three more neutrons are released and before you know it's a chain reaction has been set up and this can obviously become extremely dangerous if it isn't controlled hence the Chernobyl disaster back in the 80s so how do we try and improve the safety of the nuclear reactor well we have several mechanisms such as control rods these dip into the nuclear reactor and what they do is they absorb neutrons so clearly if you take away neutrons they can't collide with any uranium so the whole reaction slows down you also have a moderator and what a moderator does is that it slows the neutrons notice the difference control rods to remove neutrons moderators slow the neutrons so they lower the kinetic energy meaning that they collide with less energy and therefore subsequently of the reaction is made safer you might find there's a coolant and that's just called water which should remove some heat from the reaction and you'll also see that it is contained within a big lead box or concretes and that's to improve their safety to make sure that people that work in the nuclear reactor don't get exposed to radiation now the type of energy released is going to be kinetic energy and the kinetic energy is converted to thermal energy which is used to heat water that water turns into steam and steam turns the turbines and the turbines Tanager and that's how the electricity is actually produced from a nuclear reactor there are disadvantages although this is a great way in which we can produce electricity only in a very small amount of uranium in order to generate huge amounts of electricity it is extremely dangerous the radioactive waste remains radioactive for many years it needs to be stored safely underground and make sure that it can't contaminate water sources which we drink it has high decommissioning costs and that's to do with how you actually take apart the nuclear reactor once you are done with it and that's obviously due to the safety aspects and it also has high startup costs we're building it in the first place will be extremely expensive 11 in a nuclear reactor uranium-235 nucleus absorbs a neutron and fish and occurs complete the equation below that shows the typical fission reaction please don't find this totally overwhelming we can work it out so we've got uranium-235 going in and a neutron is fired at it leading to I think that's barium and Krypton being produced as a smaller nuclei and three neutrons given off so basically it's like just like maths or algebra or something you just need to make sure that whatever you started out with which was uranium-235 everything else produced after that has to add up to 235 you can't just randomly lose matter so effectively what you need to do is add 142 to one and also to one because that's the neutrons accounted for and then if you add those all up and take them away from 2 3 5 you'll get an answer which is 91 and that needs to go here and then the same below you've now used got a proton number an atomic number of 92 and we can see zero against the neutron so we'll need to worry about is the Krypton 36 so just do 92 take 36 and you'll get an answer which is 56 be explained how nuclear fission can lead to a chain reaction so for the first mark you want to say that the neutrons are released that these are then absorbed by other uranium nuclei and this causes further fish and reactions for another mark you could have said that neutrons are slowed by the moderator but I don't really know why you'd think to write that particularly see the diagram shows a nuclear reactor on the diagram label the control rods and the shielding so the black things hanging down here are the control rods and the shielding is the Box on the outside which prevents excess radiation getting out explain while shielding is needed you need to talk about the fact here that the reactor material or the waste is radioactive and then the second mark that can lead to cancer which is very dangerous so that's why you obviously need to shield it and keep it away from people and the reason why you do need shielding is because remember that radiation is very penetrating it will pass through a huge amount of air so you do need that concrete box around it we rented getting out 12 the diagram shows the main parts of a nuclear reactor so we've got our control rods moderator fuel rod shielding reactor vessel and coolant in do you remember the control rods absorb excess neutrons and the moderator removes the kinetic energy and the moderator reduces the kinetic energy of the neutrons the fuel rod will obviously provide the source of uranium anyway draw a straight line linking each part of the reactor to its correct purpose so I've already accidentally said what the control rod does which is that it absorbs neutrons I'm going to go to a fuel rod because that's the next easiest one to answer remember that contains uranium the moderator I said decreases kinetic energy which is the same as slowing them the reactor vessel keeps radioactive material inside the reactor that makes sense so the coolant transfers thermal energy that also makes sense which of these is a nuclear fission product should remember that's what is made after nuclear fission takes place and remember nuclear fission is the splitting of the atomic nuclei which releases neutrons which is why see as the answer here describe the process of nuclear fission so neutral a neutron is fired at the uranium-235 nucleus and the nucleus splits producing two daughter nuclei and up to three extra neutrons and I've actually already said three or four marks worth of things and you can say that kinetic energy is released state three ways in which nuclear fission differs from radioactive decay remember nuclear fission is a human artificial process whereas radioactive decay occurs naturally so start by saying that decay is a random process which occurs naturally whereas fission is not random it's due to humans firing neutrons uranium-235 you want to talk about the fact that fission produces to daughter nuclei whereas decay only produces one and remember that alpha and beta or gamma are produced by decay whereas in nuclear fission either alpha or beta gamma are released instead it simply daughter nuclei and neutrons so let's start by looking at the solar system so the solar system contains all the planets that you guys have heard of and in order starting closest to the Sun you have Mercury Venus Mars Jupiter Saturn Uranus Neptune and sometimes people can't please her but I don't think we're supposed to cancer anymore because it is too small to be counted as a planet you saw me do my thing of me remembering this the way I remember the order of the planets is my very easy method just speeds up naming and that is a great mnemonic for how can you remember the order of the planets now more terminology we need to look at things like the galaxy a galaxy is made up of billions of stars so it's a collection of billions of stars what is the universe or the universe is made up of billions of galaxies so we on earth are living on a teeny tiny planet which exists in a galaxy the galaxy you do need to know the name of it's the Milky Way and the Milky Way is just one of billions of galaxies which make up our universe so yeah it's kind of mind-boggling I try not to think about it too much because it freaks me out now what holds all the planets in position that is gravitational pull and thus will keep everything in position so for example it keeps planets orbiting the Sun it keeps moons orbiting planets it keeps artificial satellites orbiting the Earth for example and lastly it keeps comets orbiting the Sun do you remember the satellite is any object which orbits the planet there's both artificial and natural satellites artificial ones are ones which are man-made that we have placed into the sky whereas natural one is one such as the moon now comets as with planets have elliptical orbits which means they have an oval orbit they don't have a perfectly circular one the thing you'll notice with comets is they have very elliptical orbits that can very squash circle and what that means is the comet travels fastest when it's closest to the Sun due to increased gravitational pull and travels more slowly further away from the Sun now what dictates the strength of the gravitational pull that will be both the mass of the planet in question so larger planets have a strong occasional and also the distance from the Sun so the farther away our planet is from the Sun the less strong the gravitational pull will be the diagram shows the orbits of some objects in the solar system path x is the orbit of a so if you have a look at its path it is pretty much circular which means it can't be a comet it's orbiting the Sun which means it must be a planet so that it's C pathway is the orbit of a we've got an extremely elliptical or oval orbit which sometimes takes the object close to the Sun and other times takes it really far away and this is characteristic of a comet and the objects are held in orbit by remember this is gravitational force which is option C we now need to look at a life cycle of stars both very large stars and stars which are smaller like our Sun first of all we need to understand the term nebulae now a nebula is just a big cloud of dust and gas and us beginning other stars like we're going to take a small star to begin with such as our Sun and we're going to look at its life cycle so to begin with that nebula that big old ball of gas and dust needs to be brought together how do gravitational pull so it pulls together all that dust and gas and then at that point it can start burning fuel and the fuel in question is hydrogen because the hydrogen nuclei come together we call that a nuclear fusion because they're fusing and they released a huge amount of both light and thermal energy at this point the stars in its main sequence it's like the adult part of its life it will eventually run out of hydrogen fuel and it will start burning helium and then it will swell up to form a red giant then at this point it turns into a white dwarf and then when it totally runs out of fuel it will turn into a black dwarf large stars so very very large stars have a slightly different lifecycle they start in the same place which is that they have a nebula so the huge dust cloud gas cloud will be pulled together through gravity then it will enter its main sequence and will start burning through its hydrogen fuel again nuclear fusion is occurring however this time when it runs out of fuel it woman talyn's for huge events supergiant's and then at this point a huge explosion occurs called a supernova I love that word and then depending on the size of the star it will leave a forming neutron star and if the stars very very massive it will form a black hole which you probably heard of from films very hot styles of a pair blue and the cooler stars appear red and the million stars appear orange so now I need to talk you through the orbital speed part of the paper I'm just going to do the whole of this question because it's all relevant a this question is about planets in the solar system the planets in the solar system have different sizes and masses the bar chart shows the gravitational field strength strength of each planet compared to earth and we can see Jupiter has the largest gravitational field strength which makes sense because it's the largest planet therefore it has the largest mass so in order to answer this question remember the equation weights equals mass times gravitational field strength the mass is staying the same because if you look at all the options below that will one kilogram so it's just a matter of using the graph to work out which gravitational field strength is the greatest so let's look at option a a one kilogram mass with way more and Venus than on Neptune have a look at the graph that's incorrect a one kilogram mass would weigh more on earth than on Uranus that is correct because the bar for Earth is slightly higher than that for Uranus but as all good scientists should do keep checking the final two options a one kilogram mass would weigh more on markku then on Saturn that is incorrect a one kilogram mass would weigh more on Mars than on Jupiter also incorrect on earth the gravitational field strength is 10 which of these is the by the gravitational field strength on Mars we know that the gravitational field strength for Earth is 10 and we use the graph and we can see that it has been given as one so obviously 10 is 1 times 10 so we need to do the same calculation when we get Mars to read off we can say see it's 0.4 multiplied by that 10 and that gives to serve ru of 4 damos is a natural satellite of Mars damos has an orbital time period of 1820 minutes an orbital speed of 1,350 meters per second to calculate the orbital radius and we've been given the time period and the orbital speed so I like to underline those and just have a quick look down here where in meters so we're looking at standard SI units everywhere and this here needs converting because minutes is not the standard SI unit so obviously we need to convert that to seconds by doing 1800 20 times 60 to get 100 and 9200 then we're going to write this equation V equals 2 pi R over T so V stands for orbital speed R is for the orbital radius T is for the time period it's a matter of substituting in numbers so we know that the orbital speed is 1,350 2 pi we're looking for our we've worked out the time period is this number so how do we get rid of that 100 9200 you have to times both sides by it three times by that both sides and that means 1,350 times 100 9200 to get this very large number which I'm not even going to attempt to read it cos 2 pi R to get our bite site itself just divide both sides by 2 pi so keep that number in your calculator and divide by 2 pi and R will therefore equal this large number again and it's up to you how many significant figures you want to give it to you seeing as they haven't specified so I'm going to write it like this the diagram shows damos an orbit around Mars which hour shows the direction of the force of gravity that Mars exerts on damos that would be like this so it's a and that's because Mars is attracting damos the moon to itself so we're done well done for staying all this way I'm really impressed if you manage to watch the video all in one don't forget about my revision guides my perfect answer vision guides are available on my website right now at WWII so Cody can you can click on this card to buy yourself a copy of my revision guide which makes the perfect accompaniment to these videos [Music]