hello l in this video we're going through everything you need for physics paper one to a foundation level so you don't need to wor about anything in here that's for highy or for separate science so take things slowly take things carefully make notes when you finish you can try free questions the free flash card and the prity papers over on the [Music] [Applause] website I want to start off here by looking at prefixes these are used throughout physics through all of the topics to describe the order of magnitude of a quantity and when we're doing calculations we need to make sure that we use the SI unit so if they give you something such as milliamps we need to convert it to amps so we need to know that Terra means time 10^ 12 it's a very big number Giga is * 10 9 Mega is * 10 6 kilo is * 10 3 CTI like centimeter is * 10- 2 Milli is time 10us 3 micro which is this little Greek symbol a bit like a curly U is time 10 the - 6 and Nano is time 10- 9 and you'll see here that I've highlighted out the CTI one and the reason I did that is I just want you to imagine if that wasn't there notice the pattern with the numbers they're going down by three each time this is a really easy way to remember these so all you need to do is remember the order of these prefixes and then you can work out the order of magnitude so an example of how we might use this in practice is if we're told that we have 40 milliamps for example but we need to calculate something using that value we will need to rewrite it in just amps so in place of the M for Millie we write time 10us 3 so 40 milliamps is equal to 40 * 10 Theus 3 an please do make sure that you get these memorized we need to know about energy stores and systems a system is an object or a group of objects we might refer to a Clos system which is a system when energy can't Escape or enter the system so closed systems are particularly important because in a closed system the total energy remains constant however the energy may be transferred between its stores so getting on to energy stores we need to know the following ones we need to know about kinetic energy gravitational potential energy elastic potential energy internal or thermal energy chemical nuclear magnetic and electrostatic energy so kinetic energy is the energy of a moving object an example of this is a moving car gravitational potential energy is the energy an object has when it's raised above the ground so an example of something with gravitational potential energy is a book on a shelf elastic potential energy is the energy an elastic object for example a spring has when it's stretched or compressed internal or thermal energy is the total kinetic and potential energies of all the particles within an object an example of this is a hot cup of tea then we've got chemical energy this is the energy stored in chemical bonds an example of this is a battery or some food nuclear energy is the energy stored in the nucleus of an atom an example of something that has this nuclear energy is the uranium fuel in a nuclear reactor then we've got magnetic energy this is the energy that a magnetic object has when it is near to a magnetic field an example of this is a fridge magnet then we've got electrostatic energy and this is the energy that a charged object has when it is held near to another charged object this can be seen in vandag graph generators energy can be transferred between different stores using four different methods the first is heating so energy will be transferred from one object to to another if there's a difference in temperature a temperature gradient and it will travel from the hottest to the coolest radiation is another way we can transfer energy and in this case the energy is transferred as a wave an example of this is infrared radiation from the Sun then we've got electrical work this is the energy transferred by the flow of charge due to a potential difference finally we have mechanical work this is the energy transferred due to a force moving an object through a distance or changing its shape so an example of an energy transfer is a book falling from a shelf initially that book on its shelf had a gravitational energy store however that was transferred mechanically by the force of gravity to the kinetic energy store we need to be able to say different energy transfers dependent on a scenario given to us in an exam kinetic energy is the energy of a moving object so the equation for this is kinetic energy equals half * Mass * velocity squared or the simple equation of this is ekal a half mv^2 so the units of kinetic energy is jewles the units of mass is kilog and the unit of velocity is me/ second elastic potential energy is the energy stored in a stretched spring the equation for elastic potential energy is equal to2 time spring constant time extension squared so if we were to do this just using the symbols that would be e with a little e is equal to a half K E2 where that little e there is the extension measured in meters K is the spring constant measured in NE per meter and the elastic potential energy is measured in jewles gravitational potential energy is the energy gained by an object raised above ground level to calculate the gravitational potential energy we multiply together the math with the gravitational field strength and the height if we do this using symbols then that's EG is equal to M * by G the gravitational field strength Times by the height now looking at units gravitational potential energy is measured in Jews just like all of the energies are Mass is measured in kilograms gravitational field strength is measured in Newtons per kilogram and height is measured in meters specific heat capacity is the amount of energy required to raise the temperature of 1 kilogram of the substance by 1° Celsius we can calculate the change in thermal energy during a change in temperature by using the following equation the change in thermal energy equals the mass times by the specific heat capacity Times by the temperature change or if we were to use the symbol equation this is Delta eal M * C * by Delta Theta now that Delta is that little triangle symbol and whenever we see that in physics that is telling us that we need the change in that quantity so we want the change change in energy and the change in temperature which is given by that Theta symbol so in terms of units the change in thermal energy is measured in jewles the Mass is measured in kilogram the specific heat capacity is measured in jewles per kilogram per degre Celsius and the temperature change is measured in degrees celius power is the rate at which energy is transferred we can find the power in one of two ways the first way we can use is that power equals energy transferred divided by time or P = e/ T now remember power is measured in watts energy transferred is measured in Jews and time is measured in seconds alternatively we could say that power equals work done over time in this case that's P = w/ T power is still measur measured in watts time is still measured in seconds and work done is measured in Jewels we should know that an energy transfer of one Jew per second is the same as a power of one Watt and we should also be able to compare different systems if for example I was picking up a box and lifting it up to a certain height the quicker I do that the more power I have the law of conservation of energy states that energy can be transferred usefully stored or dissipated but it cannot be created or destroyed and this is a really key fact in physics that we will use all the time so when energy is dissipated it is transferred to less useful stores for example if we have a light bulb we take that electrical energy store that's inputed and it gets transferred to light energy which is useful but also thermal energy as it heats up now this thermal energy is the wasted energy or the dissipated energy it's important that we know that all energy will eventually be transferred to the thermal store of the surroundings in the exam we might be asked how we can reduce unwanted energy transfers there's two examples that they expect you to know firstly we can lubricate it and secondly we can add thermal insulation those are two ways that we can reduce unwanted energy transfers however always have a think to the context of the question for example lubrication might be useful if we're talking about things rubbing over each other because that will reduce the friction and therefore that thermal energy transfer that wouldn't be useful however I'm sure you could imagine that that wouldn't be useful for every example so try and always think about the context and think how can you reduce that unwanted energy transfer the thermal conductivity of a material tells us how quickly energy is transferred through the material via thermal conduction the higher the rate of thermal conductivity of a material the higher the rate of energy transfer by conduction across the material now there's an experiment that you may have carried out which shows this so the experiment uses dots of wax on different metal rods to compare the thermal conductivity of them now all of these rods we want to have identical lengths and identical diameters to make sure that any differences in the time it takes to melt this wax will be purely due to the material they're made of of and the thermal conductivity of those materials the rod whose wax will melt first when heated on one end is the one that has the highest thermal conductivity houses are designed to minimize heat loss houses that have a lot of heat loss are going to cost more money to heat and therefore require more fuel to heat all of these things are negative ti so the rate of energy transfer through a material such as a building's roof and its walls depends upon three things it depends upon the thermal conductivity of the material it depends on the thickness of the material and it depends on the temperature gradient between inside and outside so when we want to minimize the rate of heat loss when building a house we want to ensure that we use materials with a low thermal conductivity this is because those materials are going to have a lower rate of energy transfer P conduction this means that more of the heat would remain inside the home and not leave the home having thicker walls would also decrease the rate of energy transfer because the conduction would have to take place through a greater distance which means that that less heat loss will take place the Energy Efficiency of an energy transfer can be calculated using one of two equations efficiency is equal to the useful output energy transfer divided by the total input energy transfer so useful output over the total input alternatively if we're given Powers instead we can say that the efficiency is equal to the useful power output divided by the total power input so very similar idea it's that useful output divided by the total input now both of these equations as they stand will give our answer as a decimal now in the exam you might be asked to give your answer as a decimal or as a percentage if we needed to get the efficiency as a percentage all we do is we use these equations but then we multiply our answer through by 100 if we ever needed to increase the efficiency we need to increase the amount of useful energy transfer therefore we need to minimize the amount of energy dissipated and wasted the way that we could do this is things like streamlining things like lubrication try and stop frictions within the system which could of course lead to energy transfers into less useful forms of energy we need to know the difference between renewable energy resources and non-renewable energy resources so renewable energy resources are energy resources that can be replenished as they're used up so we can always get more of it and therefore it's never going to run out a few examples of these but we'll look at them more later include wind geothermal and so energy let's think about non-renewable energy resources then this is just the opposite it's an energy resource that cannot be replenished as it's used up and will eventually run out so there's a finite amount of that resource available so some examples of these include fossil fuels which are oil coal and natural gas and nuclear fishing now the reason why it's important we say it can't be replenished as it's used up it's because in theory we are making more oil coal and natural gas however it takes millions of years we are not making it at the rate we're using it up and this is why this is classed as non-renewable we also need to know what these energy resources can be used for they can be used for transport energy generation and heating now let's take a look at those nonrenewable resources in a bit more detail so let's think about those fossil fuels of coal natural gas and oil to start off with so some advantages of these is that there is enough available to currently meet the demands they're also relatively cheap to extract from underground and they're reliable we know what we're getting with them some disadvantages however include the fact that they are a finite resource they're going to run out another disadvantage is that they release carbon dioxide when they're combusted now this contributes to the Greenhouse Effect and global warming they also release other pollutants such as sulfur dioxide which can cause acid rain and there's a risk of oil spills which could damage aquatic environments now let's have a think about nuclear fish so with nuclear ficient another Advantage is that there is enough available to currently meet demand another the great thing this time though is that no pollutant gases are released so there's no sulfur dioxide causing acid rain there's no carbon dioxide causing the greenhouse effect is also reliable however some disadvantages of nuclear fishing include the fact that nuclear waste that's produced is difficult to safely dispose of and it needs to be stored for hundreds of years before it can become safe again nuclear waste is danger dangerous it can lead to mutations which can cause things such as Cancers and other serious conditions another disadvantage of nuclear fishing is the fact that those nuclear power plants are very expensive to build to run and then at the end of their lifetime decommission now let's have a look at the other renewable resources and we'll look at all of the different ones here so we've got solar power which is used the Sun the advantage of this is that it's cheap to run after it's installed in the first place and it also produces no pollutant Gases such as sulfur dioxide or carbon dioxide however it's not reliable we need it to be a sunny day to be able to get energy from the Sun and the initial installation to put those solar panels down is expensive and it takes a long time to recoup that benefit next we have tidal which is using the tides in the sea to get energy now this is reliable as there will always be tides and of course again it produces no pollutant Gases such as carbon dioxide or sulfur dioxide it can produce large amounts of energy which is a great advantage and there are no fuel costs involved however there are of course some disadvantages when we install the equipment needed to harness this tidal energy we can damage Marine habitats this installation is expensive and an issue is is that we can't control the supply we're dependent on the time of the month according to the tides we can't say oh we need a lot of energy now so let's turn it up a bit no we can't do this unfortunately we're unable to control that supply and get more when we need more we're limited by the tides according to the time of the month now we've got hydroelectric energy so these use hydroelectric dams once these are installed they're cheap to run and there are no fuel costs and they're reliable and we can control the energy Supply dependent on demand however there are again some disadvantages when we build this hydroelectric Dam initially it costs a lot of money and is very expensive we will also destroy some habitat when we set this up which can be a big problem wave energy is another source of energy that uses waves to generate it this is cheap to run there are no fuel costs and no pollutant gases like sulfur dioxide or carbon dioxide are formed however this can again damage Marine habitats and the installation is initially very expensive another issue is that we're unable to control Supply it depends upon on the weather because we have bigger stronger waves in certain weather conditions compared to others now very similarly we're on to wind power so wind again is cheap to run there are no fuel costs and no pollutant gases are released however we have certain problems wind turbines are very noisy so noise pollution is an issue we're also unable to control Supply as just like the wave and energ it's weather dependent another disadvantage of wind energy is the fact that for large scale demand we're going to need a lot of wind turbines and therefore we're going to need a lot of land that could be used for other things next we've got geothermal energy this is again cheap to run there are no fuel costs and it produces no pollutant gases however installation is very expensive and are limited locations that we can set this up finally we have biofuels now biofuels are reliable because the supply can be controlled dependent on demand so when there's a high demand we can make more they can also be carbon neutral because as you grow the plants needed for biofuels they're going to take in carbon dioxide using photosynthesis and then when they're combusted they will release it back into the atmosphere so they are carbon neutral however some disadvantages of biofuels is the fact that they can lead to deforestation and they are expensive to produce so make sure that you can say some advantages and disadvantages of all of these different renewable and non-renewable resources [Music] [Music] [Music] in the electricity topic we really do need to know the following electrical component components we need to be able to draw them and recognize them so let's start off with the switch we can see it open and closed we know that a cell is two little parallel lines one's bigger than the other and a battery is several of these cells could be two could be more than two that's what makes up a battery several cells then we have the lamp which is a circle with across through it a fuse which is a rectangle with a line going all all the way through it a voltmeter is a circle with a v in it and of course we need to know that a voltmeter is used to measure voltage an ameter is used to measure current and its circuit symbol is a circle with an a in it ather Amer a thermister is a rectangle with a tick through it it's really important that we recognize that this rectangle with no line through it is resistor so different variations of these rectangles are going to be different types of resistors so an ldr is a rectangle with two lines going towards the rectangle you may see it with a circle around it but you may also see it without that Circle and this is a light dependent resistor and that's why the arrows go towards it because it depends on the light so the light's shining on it and it's a rectangle because it's a resistor then just a plain old resistor is simply a rectangle a variable resistor is a rectangle with an arrow going diagonally through it and a diode which is a component which only lets current flow in One Direction is a triangle pointing in One Direction with a line on the end of it and sometimes this may have a circle around it sometimes it may not but they both represent a diode and finally we have an LED or light emitting diode this is just the same symbol that we have for diode so this triangle with a line on the end of it but this time because it's emitting light we're going to point two arrows away from the diode to show it's a light emitting diode an electrical current is the rate of flow of electrical charge and by electrical charge we could be talking about electrons or ions we we need to know the following equation for this we need to know that charge flow is equal to the current Times by the time it can often be helpful to use this as the symbol equation just because it's quicker to write in this equation we represent charge flow with a Q current with an i and time with a t so we can say that Q equal I * T now it's important that we know that charge flow is measured in kums current is measured in amperes or amp and time is measured in seconds so if we ever have a Time given to us in hours or minutes we do need to convert it to seconds now of course everybody's math skills is slightly different some people struggle with rearranging this equation and some people prefer to use the triangles now all I care about is you getting all of the marks in the exam I do not care how you get it at all okay some teachers can be a bit Smooty about triangles but I just want you to get the marks so if you do struggle with the algebra this can be really helpful for rearranging the equation say if we needed to find current so the bit which is times together always goes on the bottom of a triangle so we've got Q on the top I * t on the bottom and if we wanted to get I all we'd need to do is cover the I with our finger and we can see Q over T and so that's it so the current is equal to Q over T so now we that let's remind ourselves that for electrical charge and therefore a current to flow we need to have two things we need a closed circuit so no breaks in it and a source of the potential difference now this could be a cell it could be a Main's power pack it could be a battery and what we'll find is that the current is going to be the same everywhere in a single closed loop the current that flows through a component depends on two different factors so the resistance of the component that it's flowing through and the potential difference through that component we need to know the relationship between potential difference current and resistance so we need to know that the potential difference is equal to the current times the resistance and again we'll find that using the symbols can just be a quicker way to write this down and so we might see this as v = i * R where V is potential difference it's voltage current is the i and r is the resistance so potential difference is measured in volts which is V current is measured in ampir or amps which is a capital A and resistance is measured inms which is the Greek symbol Omega so again we can use a triangle if you struggle with algebra here remember that the bits times together always goes on the bottom so here we've got a v on the top an i times are on the bottom and now you should easily be able to find whatever term you're asked to find now for a given potential difference we need to know that if we increase the resistance we're going to decrease the current and that's because if we increase the resistance it's harder for that current to flow it's a bit like making a pipe narrower and so that means less current less of this charge is going to be able to flow through the circuit but like water flowing through a narrower pipe in some resistors we'll find that the resistance remains constant even when the current increases or decreases now this is said to be an omic conductor it obeys OHS law ohms law tells us that the potential difference and the current are directly proportional to each other and therefore have a linear relationship so what we'll see here is in an omic conductor at a constant temperature the resistance remains constant as the current increases however we'll find that the resistance of some different resistors actually changes as the current changes so an example of this is a filament lamp now filament lamps have tiny little wires within them and the way that that lamp works is the current goes through them they get hot and they start to glow and that's how they illuminate the room however as the current increases the filament is going to get hotter and hotter if you imagine all of the atoms within that really hot wire they are going to be bouncing around the place and what that means is that it's harder for the current to flow imagine trying to walk down the street and everyone's just running around the place you're going to be knocking into people all the time and you're not going to be able to walk as quickly that's why as the current increases and the filament gets hotter the resistance is going to increase now this doesn't obey a linear relationship this shows a nonlinear relationship and actually the resistance increases as the current increases another example of a resistor whose resistance changes as the current changes is a diode now a diode is a very important type of component it's one where the current only Flows In One Direction and the reason for this is that the resistance in the reverse direction is very high now this is shown in our IV graph for the diode we can see that in this negative direction there's actually no current flowing however when the current flows in the positive direction you can see that as current increases the potential difference increases too and an extra thing I just want to clarify and make sure that you know this is going to be the same graph in LED as well don't be afraid and think because it's not diode alone it's going to be different we're going to see this exact same graph for LEDs and for diodes make sure you learn it another example of a resistor whose resistance changes as current changes is an ldr ldrs or light dependent resistors are particularly interesting because their resistance is affected by the Light intensity and as the light intensity increases the resistance decreases now this can make them really useful for lots of applications such as lights which are sensitive to the dark a good example of this is street lights they only turn on when it starts to get dark so perhaps they have an ldr in their circuit to ensure that this happens the last resistor we're going to have a detailed look at here is the thermister now the thermister is very similar to an ldr in how it behaves except instead of light intensity they're affected by temperature so the resistance of a thermister is affected by the temperature and we'll see that as temperature increases the resistance decreases now again a bit like ldrs this makes thermas very useful for a lot of applications an example of a use for therm is a thermostat most people have thermostats in their homes where they set a certain temperature for their Central he heting to come on when it gets a bit too cold and this ther would be able to enable this to happen now we need to know how we can build a circuit to measure the resistance of a component such as a resistor however it could be something such as a bulb thermister or anything really so the two key facts that we need to know is that we need to have an ameter in series with this component to measure its current and we need need a voltmeter in parallel to measure the potential difference you can see what this looks like in the diagram here a very common six mark question that we're likely to see in the exam will ask us to investigate the IV characteristics of a component and they may name the component but remember the method is going to be exactly the same regardless the first thing that we need to say is that we need to connect a battery to the component then we need to add an ameter in series and of course we then need to add a voltmeter in parallel next up we're going to need to add a variable resistor in series with the component now this is very important because we can use the variable resistor to change the potential difference so once our circuit is all set up and make sure in the exam you draw this circuit just like I have here but with the relevant component in place of this resistor we then want to record the potential difference on the bolt meter and the current on the ammeter once we've done that we now want to use our variable resistor to change the potential difference we're now going to record the new values for potential difference and current we're going to repeat this process by changing the potential difference using the variable resistor several different times until we get enough different pieces of data now we're going to do do something quite clever we're going to reverse the power supplies and this is can to be done by something as simple as just changing the direction of the battery once we do that we're going to repeat this whole process of changing the potential difference again using the variable resistor but this is now going to give you negative values for current because the current is going to be flowing in the opposite direction so once we've repeated this several times we're now going to get all of our data and we're going to plot a graph of current against potential difference and that is going to give us one of these graphs that we've seen earlier where we have a relationship between current and voltage so circuits can be connected in two ways of course we have our series circuit where there's a single Loop and then we have our parallel circuits too now it's important that we know a few facts about series circuits and parallel circuits so in a series circuit we should know that the current is the same in each component now this comes down to the fact that current is the flow of charge imagine you've got cars driving around one Loop you're going to have the same amount of cars just driving through the whole Loop aren't you they're not got anywhere else to go so current is the same in each component however the total potential difference is shared between the components and the reason for this is the fact that potential difference is actually the work done per unit charge it's an energy and so that energy is going to get shared as it goes through each of these components now total resistance on the other hand is the sum of the resistance of each component so we need to know that if we saw this example for instance the total resistance would be the resistance of bulb one plus the resistance of bulb two if we were to look at parallel circuits though because we've got these different Loops again if we think of those cars moving along it when it gets to the little Junction there's two options for where the cars or the current goes so the current will split between the different Loops potential difference however is the same in each component and the potential difference is the work done per charge and each of those charges are just each going through one component so it's exactly the same for every one of them regardless of which route they took total resistance however in the parallel circuit is a little bit different it's actually less than the resistance of the smallest resistor in the circuit we don't however have to do any calculations for the parallel circuits at GCSE just the series circuit Why does adding resistors in series increase the total resistance well this is just simply the fact that the current has more resistors to pass through however when we ask the question of Why does adding resistors in parallel decrease the total resistance it's a little bit more complicated so the parallel Loops are going to add an additional path for the current to flow through and so more current can flow in total even when the potential difference Remains the Same Again if we think of cars for instance this really makes a lot of sense if another route opened up then suddenly the car and the traffic it's going to flow much more freely and therefore just like the current that flow will increase and this is why adding additional paths for that current flow through is actually going to decrease the resistance leading to more current flowing so Main's electricity which we have in all of our plug sockets is an alternating current Supply now what this means is that the current is repeatedly changing direction and AC current is produced by an alternating potential difference however on the other hand batteries that we use to put into our remote controls for instance or having our phones or our laptops they provide a direct current now in a DC Supply the current flows in Only One Direction and it's produced by a direct potential difference at GCSE we need to know a bit more information about our Main's electricity Supply so of course we know it's an alternating current Supply or AC however we also need to know that it has a frequency of 50 htz and a potential difference of 230 volts in the United Kingdom most of the electrical appliances are connected to the main Supply using a three core cable now this is a really safe system so we're very lucky to have it in this country now these three different wires in the Three core cable are colorcoded and this is so useful because it means we can easily identify them and keep ourselves safe so the Live Wire is brown the Earth wire is made up of green and yellow stripes and the neutral wire is blue now as well as knowing the color of these different types of wires we also need to know the role that they play and what potential difference goes through them so the Live Wire is the most dangerous wire it carries the alternating potential difference from the main Supply so it carries a voltage of 230 volts now the Earth wire which is made up of green and yellow stripes is the safety wire and this is very important because it prevents the appliance from becoming live now the only time that the earthwire will ever carry a current is if there's a fault in that Appliance but again the purpose will be to keep it safe so the potential difference normally then going through that Earth wire is 0 volts finally our neutral wire that's blue in color this is here to complete the circuit and this has a potential difference of zero volts now let's have a look at some other key features to the plug so we can see here that we have a fuse in this plug why do we have these fuses well the reason for this is that if the current gets too high a thin wire inside that fuse will melt and the importance of this is by melting this is going to break the circuit now of course we know that when we break the circuit electricity is no longer flowing and this prevents the risk of electrocution so it makes it much safer now we can also see here we have a cable grip now the importance of this is it holds the wires in place now we'll see that the cable grip as well as other parts of the wire such as the flex and the actual plastic casing is made of the material of plastic now the reason why we use plastic is because it is a good insulator however the wires are made up of copper and they're coed in plastic now the reason why we use copper in the actual wires is because Co copper is a good conductor of electricity we need to know why a live wire might be dangerous even when the switch is open and this is a really important question because of course if the switch is open you might think that the current can't flow however if we were to touch the Live Wire we could ourselves complete the circuit and this is because we are of course in contact with the ground and so that current will flow through our bodies into the ground so we could be electrocuted and that's why that live wire is always dangerous even when the switch is open we also need to know what the danger is of connecting the live wire to the Earth wire now this is a very similar answer to what we just said if the Live Wire came into contact with the Earth wire the circuit would be completed and this increases the risk of electrocution or fires so you can see there's so many important safety rules that we need to know when using plugs however they are designed to keep us as safe as possible we need to know how to calculate the power transfer in a device and we can relate it to the current and potential difference using this equation power equals potential difference time current or p = V * I again if your math skills are a little bit dodgy you can always use a triangle to help you rearrange this when needed the bit with the times always goes on the bottom so you've got p on the top and B * I on the bottom now remember that power is measured in watts potential difference is measured in BTS and current is measured in ampir or amps which is that capital A we can ALS Al calculate the power transfer in a device using the current and the resistance now this equation's a little bit trickier because it's power equals current squared time resistance don't forget that squared so using the symbols that would be P = I2 I for current time R and remember of course power is measured in watts which is a capital W current is measured in amp or amps which is a capital a and resistance is measured in ohms which is that Greek symbol of the Omega sign electrical appliance that we have in our home all over the place are specially designed to transfer energy from one store to another so an example here is the washing machine washing machines take electrical energy from the main Supply and transfer it to the kinetic store of the washing machine and they do this to rotate the drum and to wash your clothes so the toaster is another example of an appliance again the toaster takes electrical energy from the main Supply this time to the thermal store of that toaster heating elements now this is what enables the toaster to cook so make sure that you're able to think of any appliance that they could ask you about and give an idea of the energy transfer that takes place so the amount of energy transferred by an appliance depends on two factors first one being the appliance's power and secondly the amount of time that the appliance is on for when charge flows in a circuit we should know that work is done now we can calculate the amount of energy transferred by electrical work using the equation the energy transferred equal power * time we can use the symbols here e = p * T if we're using our standard SI units here energy transferred will be measured in Jewels which is a capital J power is measured in watts which is a capital W and time will be measured in seconds which is an S as is the case with most equations in physics we can write this in a triangle if you're not very confident with your math skills to do this we just put the P * t on the bottom remember the bit with the times always goes on the bottom of a triangle and an e on the top then for whatever it is that you want to find just cover it up with your finger and then use the triangle to get your rearranged equation for example power P equals energy over time here I've included a little top tip and this applies to any equation not just this one we might need to convert minutes to seconds we need to know that we do this by multiplying the minutes by 60 alternatively they might give you the time in hours instead and again in all likelihood we're going to need to convert this into seconds we do this by multiplying by 60 to get it into minutes and then by 60 again so multiplying by 3,600 converts hours to seconds so that we can use it in this equation now it's not common in physics if the question is about an electrical Appliance the energy may be measured in kilowatt hours now if this ever did happen then we can use this exact same equation however using slightly different units the energy transferred is now measured in kilowatt hours to be consistent with this the power would be measured in kilowatts and then finally the time would be measured in hours the amount of energy transferred can also be calculated using charge flow q and potential difference V energy transferred equals charge flow Times by potential difference or using the symbols e = q * V in this case the energy transferred is measured in Jews which is a j charge is measured in kums which is a Capital C and potential difference is measured in volts which is a capital V if you are someone who struggles with your maths we can just learn this triangle with the E on the top and the Q * the B on the bottom to help us with the rearranging side of this remember to use the Triangle cover up whatever it is that you need to find remember that the line means divide and the times mean times and then you should be able to work out anything you need using that triangle if you're stuck the national grid is the system of cables and Transformers linking power stations to homes and factories to transfer electrical power we're going to find two different types of Transformer within the National Grid we're going to find step up Transformers and step down Transformers stepup Transformers are found between power stations and transmission cables stepup Transformers are really important they're designed to increase the potential difference and therefore decrease the current now this ensures less energy gets lost through the heating of those cables this increases efficiency so more of that electrical energy is transferred from those power stations to the homes and the factories they're going to now step down Transformers on the other hand are found between transmission cables and homes and factories now step down Transformers decrease the potential difference to a lower and safer value it would be incredibly dangerous if we had potential differences as high as they were due to that stepup Transformer entering our homes the risk of electric shocks and fires would be very very high so we use step down Transformers decrease that potential difference and reduce those risks [Music] [Music] [Music] density is a measurement of how much stuff there is within an object and we can calculate the density using the equation density equals mass over volume now if we want to use the symol equation for this we need to know that density is represented by this Greek symbol row now row looks a bit like a curly P so we can say that row equals m over V we need to know that density is generally measured in kilog per M cubed Mass is measured in kilogram and volume is measured in meters cubed now to be able to calculate density in the exam we're often going to be asked to calculate the volume of different shapes so we need to make sure that we can work out the volumes of Cubes spheres cylinders and Cones let's remind ourselves of how we calculate these volumes and make sure you learn these formulas so if we have a cube like we have here we could use a ruler to measure the length of one of its sides and we can you can calculate the volume by taking that length x and cubing it so the volume of a cube is X cubed a cylinder of the other hand we need to know both its height and its diameter it's height we can use a ruler to measure and the diameter we may use Veria calipers formula here is going to be Pi * by d/ 2 SAR * by H or we may remember that from math is pi r 2 h because of course the radius is a half of the diameter if we had a sphere we would take those Veria calipers again and use it to work out the diameter of the sphere then the volume will be calculated using 4/3 pi * by d/ 2 cubed finally we've got the volume of a cone so here again we need two Dimensions we need its height from its peak up to its base and we need its diameter so to calculate the volume of a cone the calculation is 1/3 * by pi * by D / 2^ 2 times by the height the particle model can be used to explain the different states of matter so if we look at a solid for example we can see that its particles are arranged in a regular pattern they're very close together and they vibrate about fixed positions now because they're very close together solids are actually very dense now let's look at liquids so liquids are found in a random Arrangement this time particles are still close together but the particles move around each other now because these particles are still close just not very close they are still really quite dense however when we compare that to a gas where the particles are still randomly arranged but they're far apart now moving quickly in all directions it's the fact that they're far apart and therefore occupy a much larger volume that means that they have really quite a low density in the exam we need to be able to describe an experiment to find the density of an irregularly shaped object so this could be something like a stone something that isn't a distinctive shape which you have a formula to work out its volume for so here we need to know this method we'd start off by measuring the mass of the object using our standard Top Hand balance and then we're going to get a displacement can like the one in the diagram and we're going to fill it with water until the water is level with the bottom of that pipe just as we can see here we're then going to place an empty measuring cylinder under the pipe now we're going to be really careful here and we're going to drop our a regularly shaped object into the water now you can see in this example here we've wrapped some string around the stone so that that we can lower it in slowly and the reason why this is so important is if we just dropped it in then water would likely Splash everywhere and we would lose some water which would distort our results so we'll place it in and then we're going to see water pour out of this tube we're going to wait until the water stops leaving the displacement can and then we're going to have a look at our cylinder which was catching all of that displaced water and we're going to measure the volume of that displaced water now that volume is the same as the volume of your object so here then we can use the equation for density which is density equals mass / by the volume to calculate the density of that object we could also be asked to describe an experiment to find the density of a regularly shaped object such as a cube or something and here the method is a little bit simpler in a way first off we're going to measure the dimensions of the shape so we're going to use rulers to measure any lengths and Veria calipers to find diameters we're then going to measure the mass of the object using a top pan balance and then we're going to calculate the volume of the shape using those Dimensions that we found so here if we had this Cube we'd measure the dimension of its length and we're going to cube it to get that volume then now that we've got the mass and the volume we're going to use the equation for density to calculate the density of the object so in this case we'd say density equals mass divided by that volume we need to consider some potential errors that might arise when we find an object's density firstly let us consider that different Top Hand balances being used by different people may have different calibrations this could result in an error in measuring the mass also we need to consider that different measuring cylinders might have different resolutions one measuring cylinder might measure things to the smallest 1 cm cubed another might just measure it to the nearest 5 cm cubed that's the difference in resolution and this could lead to different students getting different ansers for those volumes finally we can consider an incorrect setup of the displacement can maybe they didn't add water right to the very bottom of that tube and therefore we might get different readings for the volumes because some people may have errors in their readings finally we need to know that when talking about density we might be given measurements for density in terms of grams per ctim cubed but we actually need it in kilogram per met cubed or vice versa so it's useful to know the conversion between the two so if we have a measurement in G per cm cubed and we want to convert it to kilog per me cubed we we simply need to multiply through by 1,000 conversely if we have a density in kilog per me cubed and we want to get it in grams per cm cubed all we need to do is divide by 1,000 during changes in States mass is conserved we need to know that changes of states are actually physical changes they're not chemical changes if we reverse the process the material will regain its orig properties so if we think of some of these processes that take place we should know that going from a solid to a liquid is the process of melting whereas going from a liquid to a solid is freezing so as we go back and forth there and we reverse those processes of melting and freezing the material will regain its original properties likewise when we go from a liquid to a gas that's the process of boiling whereas going from a gas to a liquid is condensed ing now the final process that we need to know one that we're probably less familiar with is the process of sublimation sublimation is the process where the state changes from a solid all the way to a gas and although we don't have quite as much experience of this I'm sure that you can visualize opening a really cold freezer and it looks like steam is coming off of the ice now this is the process of sublimation that solid ice is changing to a gas internal energy is the energy stored inside a system by the particles that make up that system so this means that it's equal to the sum all of the kinetic and potential energies of all of the particles that make up that system if we have a material and that material gets heated or cooled the material would change in one of two ways the first change is that that material might change temperature and this means that there's a change in the thermal energy store of the material so if you've heated up this material it will increase in temperature because it has gained the thermal energy store the second change that we might see is that chemical bonds may form or they may break between the particles this means that there's a change in the chemical potential energy store of the material if a material or a system sees a in its temperature the scale of that temperature change it depends on one of three factors firstly you've got the type of the material secondly the amount of energy that's been put into the system finally we've got the mass of the material the reason why the type of material affects the scale of that temperature change is because different materials have different specific heat capacities now it's really important we know the definition for specific specific heat capacity specific heat capacity is the amount of energy required to raise the temperature of one kilogram of a substance by 1° C we need to know this equation which enables us Define the change in thermal energy of a system so the change in thermal energy is equal to the mass times by that specific heat capacity of the material Times by the temperature change of the system as always we might find it easier to use the symbols for this here though we're going to see a triangle which is known as the Greek symbol Delta so we've got Delta E equals m * C that's specific heat capacity Times by Delta Theta now in this case those triangles or the Deltas refer to the change of the substance so we've got the change in energy and Delta Theta is the change in temperature so we also need to know the change in thermal energy is measured in Jews Mass is measured in kilograms specific heat capacity is measured in jewles per kilogram per degree celsius and finally the temperature change is measured in degrees C when a substance changes state we'll see that the temperature doesn't actually change during this process however the stored energy Within in that substance and therefore its internal energy does change so this is where we're introduced to a term which is the specific latent heat and we need to know that the specific latent heat is the energy required to change the state of one kilogram of a substance without changing its temperature so we've got two different variations of specific latent heat we've got specific latent heat of vaporization and specific latent heat of fusion so specific glant heat of vaporization involves changing the state between liquid and Vapor I like to think vaporization The Vapor in there somewhere the gas okay so that could be going from liquid to Vapor or vapor to liquid we will still refer to this as the specific latent heat of vaporization then we've got specific latent heater Fusion which this time is the energy required to change the state from solid to liquid of 1 kg of a substance so again specific latent heat of fusion could be talked about either going from solid to liquid or liquid to solid it will be the same we need to be able to calculate the energy required to change the state of material so we need to know this equation the energy for a change in state is equal to mass times by the specific latent heat so the formula for this is Delta e remember Delta means change which equals m * L the energy for a change of state is measured in Jews mass is still measured in kilograms and specific latent heat is measured in Jews per kilogram in the exam it's very common that we'll be asked to interpret Heating and Cooling curves let's take a look at this curve as an example so here we can see that we've got this region here here where we're negative temperature so it's very cold and we can see that we have a solid as we put energy in we're going to see that this solid gets warmer and warmer and warmer until eventually it stops getting warmer and it stays flat on this curve for a period now the flat regions these horizontal regions are where we have changes in state and so here in this case we're going to go from a solid to a liquid and all of that energy is going into breaking the bonds nothing is going towards increasing the thermal energy store so then we go on we've broken all of those bonds and now we have a liquid whose temperature is increasing increasing increasing until eventually it reaches another point it reaches the boiling point of the substance and this is where again it now goes flat and it remains horizontal for a while and that's because all of the bonds Within that liquid are going to be broken apart and it's going to now become a gas or a vapor now when we put more energy in what's going to happen is the gas is going to increase in thermal energy and therefore its temperature is going to increase now this particular curve is looking at Water I know that because I can see that it has a melting or freezing point of 0° and it has a boiling point at 100° so it's important that we know that water boils at 100° and it melts at 0° and this is actually the only material who's melting a boiling point they expect you to know just water but luckily we've got everyday experience of that so I'm sure you're familiar with those facts already in a gas the molecules are constantly moving around in random directions the temperature of a gas is related to the average kinetic energy of its molecules and therefore the higher the average kinetic energy of that gas So the faster those molecules are moving the higher its temperature and this is why heating a gas and so giving it more energy leads to an increase in its temperature if we had a gas in a sealed container and so is volume is constant and we increase the temperature of the gas we would see that the pressure increases let's think about why the particles are going to have more kinetic energy and therefore they're going to be moving around the container more quickly now if it's moving more quickly the particles are going to collide with the walls of that container more frequently this means that we're going to exert a greater total force on the walls of that container now this increases the pressure now temperature and pressure are directly proportional if we increase the temperature by a certain amount pressure will also increase by that same amount so say if we doubled the temperature the pressure would also double [Music] [Music] [Music] [Music] [Music] the atom is made up of three different types of particle so we have protons which are positively charged particles found within the central nucleus of the atom then we also have neutrons which are also found inside the nucleus of the atom neutrons however have no charge and we might see this referred to as being neutral now that third particle found within an atom is the electron now electrons are negatively charged particles and we don't find them in the nucleus this time we find them in shells which orbit the nucleus so you can see all this in our little diagram here and we have to get very used to these diagrams and being able to label them accurately we also need to have an idea of how small the atom actually is atoms have a radius of about 0.1 nanom this is of the order of 1 * 10- 10 m so really tiny the radius of a nucleus is less than 1,000th of that of the whole atom so the radius of the nucleus is about 1 * 10 -14 m this table here summarizes all of the facts that we need to know about the protons neutrons and electrons we need to know that the relative charge of a proton is + one the relative charge of a neutron is zero and the relative charge of an electron is minus1 we also need to know that the relative mass of both the protons and the neutrons so both particles found within that nucleus is equal to one however the electron relative mass is really tiny compared to this we might see it referred to in several different ways but essentially the relative mass of an electron is approximately 1 over 2,000 we may even sometimes see it referred to as just very small now it's important that we know a few key facts relating to this information so atoms of different elements will all have different numbers of protons this is part of what gives them different properties however all atoms of a particular element actually have the same number of protons now finally if we have a think about the mass of an atom we can see that the relative mass of the protons and the neutrons is so much more than that of the electrons and this is why almost all of the mass of an atom is found within the nucleus electrons are arranged at different distances from the nucleus now these distances are referred to as energy levels when the atom absorbs electromagnetic radiation this can cause the electrons to become excited and move to a higher energy level the diagram here shows us this the radiation comes in and the electron absorbs the radiation and moves to a higher energy level further from the nucleus if we think about it the other way around though if the atom was to emit electromagnetic radiation the electrons may move to a lower energy level again closer to the nucleus in chemistry we will often see Isotopes coming up now we need to know what is an isotope Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons here you can see I've got two different different isotopes of helium the helium 4 isotope has two protons two Neons and two electrons however the helium 3 isotope has two protons only one Neutron and two electrons so notice here the thing that makes these isotopes of each other is that they still have the same number of protons however they have a different number of neutrons now let's have a think about the ion what is an ion an ion is a charged particle which forms when an atom or a molecule gains or loses an electrons so here I've got a diagram of a buril atom I can see that it has four electrons now the buril atom can lose the two electrons within its outer shell to become a buril ion now because it's lost two of these negative electrons it has become more positive think about it like if you lose a negative thought and you become more positive and happy that's exactly what this pilion has done so because it's lost two electrons it now has a two plus charge and this is how we would represent this in an [Music] exam now let's have a look at how the atom is represented on the periodic table now the biggest number is known as the mass number the mass number is very important because it represents the sum of the number of protons and the number of neutrons now the smallest number of the two is the atomic number and the atomic number gives us the number of protons within that atom so so much information given just from this periodic table so it's important that we know atoms have no overall charge now that then leads us on to the fact that in an atom the number of protons those positive particles must be equal to the number of electrons those negative particles and that's how they can have no overall charge here we're going to have a look at the development of the model of the atom through time so we started off with Dalton's model Dalton's model told us that the at was a solid sphere cannot be created destroyed or divided into any smaller parts now different types of spheres made up different elements but this sphere did not contain any protons neutrons or electrons now over time JJ Thompson came along and proposed a new model called The Plum Pudding model here he said that the atom is not actually a solid sphere what it actually is is a cloud of positive charge with negative electrons embedded within it next came along the nuclear model and the experiment that determined this was Rutherford and his students Alpha scattering experiment now what Rutherford and his students did was he fired alpha particles at a thin sheet of gold foil now if the plum pudding model was true we would expect all of these alpha particles just to bounce back however most of them passed straight through some of them were a little bit deflected and very very few came straight back now what this told us was that the mass of an atom was actually concentrated in a central nucleus which had to have been positively charged to have repelled this positive alpha particle and most of the atom actually was empty space completely contradicting the plum hudding model and we know this because most of these atoms went straight through the gold foil with no deflection so over time or came up with the electron shell model and the electron shell model told us that rather than just randomly floating around the nucleus the electrons were actually found in fixed distances from the nucleus orbiting it in shells later experiments found that the positive charge of any nucleus can actually be subdivided into a whole number of smaller particles of equal charge these were named protons finally James Chadwick carried out some experiments that provided evidence to show the existence of neutrons in the nucleus and this more or less brings us to our upto-date understanding of the atom some Atomic nuclei are actually unstable unstable nuclei will randomly emit radiation to become more stable now this is the process of radioactive decay now there's different types of radiation emitted from the nucleus we need to know these four we have alpha particles beta particles gamma rays and neutrons now we need to know a bit more information about the nature of alpha beta and gamma radiation Alpha is represented by the Greek symbol Alpha the nature is that it's two neutrons and two protons or we might describe it as a helium nucleus and the change in the nucleus that emitted the alpha particle will be a loss of two neutrons and two protons to its nucleus now let's have a look at beta radiation beta radiation is represented by the Greek symbol beta and its nature is that it's a fast moving electron ejected from the nucleus if we think about the change that we see in the nucleus that emitted it we're going to see a neutron decaying into a proton and an electron which was of course that beta particle finally we have gamma radiation this is represented by the Greek symbol gamma and its nature is that it's electromagnetic radiation emitted from the nucleus the change in the nucleus will be that some energy is transferred away from the nucleus when that gamma rate is emitted activity is the rate that an unstable nucleus decays and we measure activity in beels which is represented with a capital b and a little Q we also need to know about the term count rate now count rate is quite similar to activity count rate is the number of decays recorded per second and we can detect this using a geiger M tube like we can see in this diagram here and we'll see the distinctive clicking sound when radi is present and that clicking sound will get more frequent when there is more radiation a higher activity in count rate Alpha radiation has a very small penetrating power it can be stopped by skin or by a sheet of paper it can also not get very far when it's in air it can only travel less than 5 cm in air however it has a high ionizing power now for this reason alpha particles aren't actually that dangerous if they're sat on the table in front of us probably they won't be able to travel as far as our bodies and even if they did they would be stopped by our skin however if we were to swallow them they would be very dangerous because they would get stopped by all of our internal tissues and cause damage beta radiation now can travel further its penetrating power is that it is stopped by 3 mm M of aluminium foil and it can travel a meter in air however its ionizing power is low finally we've got gamma radiation this is stopped by a thick layer of lead or concrete it can travel a kilometer in the air however its ionizing power is very low try notice here the pattern and the trend as you go down from alpha through to Beta how the penetrating power increases as does its range in air however its ionizing power decreases we can use nuclear equations to show radioactive decay we need to know the symbols for Alpha and beta radiations to do these equations Alpha radiation can be represented in two ways either you can represent it with an alpha particle with a four to the top left and a two to the bottom left or you could have the H E for helium and again a four on the top and a two at the bottom now with beta radiation we can represent this again in one of two ways either you can use that Greek symbol for beta with a zero in the top left and a minus one on the bottom left or you can do the same numbers but with an E representing that fast moving electron that beta is now alpha decay is going to cause both the mass and the charge of the nucleus to change remember that top number is the mass number and the bottom number is the atomic number which is the same as the number of protons it has and therefore it's charge so this is what the general equation looks like you can see that if x has a mass number of a and an atomic number of Zed that number a goes down by four and Zed goes down by two that's to balance it now this is easyest seen in practice if we look at this example here we can see if we just look at the top numbers that we've got 226 equal 222 + 4 and of course that is correct so we can see that the mass number has decreased by four then on the bottom the atomic numbers which represents the charge of these nuclei we've got 88 and then on the other side we've got 86 + 2 now that is balanced so we can see that the atomic number has decreased and gone from 88 to 86 Now Beta Decay because that top number was Zero the mass doesn't change only the charge of the nucleus due to the bottom number now here we can see that the top number has stayed the same however the Zed has decayed to give us Zed + 1 so an example of this is we've got 14 goes to 14 + 0 along the tops and on the bottoms though we've got 6 = 7 - 1 don't get confused with the fact that that atomic number goes up during the Decay the reason for this of course is that the charge of that electron that beta particle is minus one so the charge of the new nucleus has to have increased to balance that so of course here we've seen that the mass number has stayed the same but the atomic number has has increased by one radioactive decay is a random process this means that it is impossible to predict which atom will Decay next a term we're going to see used a lot is halflife halflife is the amount of time it takes for the number of radioactive nuclei of an isotope in a sample to half we could also say that a halflife is the time it takes for the count rate or the activ ity of a radioactive source to half if we look at this example here we can work out the half life using this graph and this is a common question that we get so looking at this curve we can see that it starts at 100 GS let's half this then because we're going to have half the mass once half the nuclei Decay half of 100 is 50 we read along hit the curve and go down and then we read it off the axes so here we have 4.5 billion years is the halflife of this particular isotope and we're just going to repeat that method when you're in the exam radioactive contamination is The Unwanted presence of radioactive atoms on other materials so an object that is contaminated is radioactive however there's a similar word that we can often confuse with contamination which is irradiation IR radiation is different though IR radiation is the process of exposing an object to nuclear radiation so that we've had exposure whereas contamination atoms were present and an object that is radiated does not become radioactive so we need to make sure we know the difference between contamination and a radiation this table summarizes it nicely so contamination occurs if Radioactive atoms get onto a material whereas a radiation occurs if an object is exposed to nuclear radiation with contamination the object is radioactive for as long as the atoms are on it however with a radiation the object has not become radioactive finally contamination is very difficult to remove because we're talking about atoms however a radi ition to remove it we simply need to remove the source or add some shielding we need to know how we can protect against contamination and irradiation so we can do this by keeping a distance from the radiation we might use tongs to handle radioactive substances rather than our hands we want to limit the time of exposure to the radioactive source so don't spend too long next to it and also use shielding so we can do this by storing our radioactive substances in a lead-lined box or by wearing protective clothing so we also need to know why it's so important to publish the findings of studies into the effects of radiation on humans this is to ensure that other scientists can peerreview this work peerreview is very important and the scientists will check that the research is valid original and significant ouch this is why in some videos I explain scratches [Music]