revising required practicals is absolutely essential for GCSE physics paper 2 They come up every single year and they also help you understand different parts of the physics course So the ones for paper 2 for AQA are Hook's law acceleration of a car or an object down a slope uh waves on a string and in water via ripple tank infrared radiation and there's a required practical on reflection or refraction that you only need to know about if you're studying separate science So for each of these practicals we're going to look at a perfect six mark method what the independent dependent and control variables are any graphs you might need to draw how do you make the experiment as accurate as you possibly can and how do you make it as safe as you can and what kind of different methods or unusual equipment could they give you in an exam question uh just to put you off a little bit So there are five of them We're going to start off with Hook's law So you have the setup with a clamp stand and two clamps on it One for your spring one for your meter ruler They have to be parallel to each other More on that later So how do I write the method Well first thing first hang the spring from the end of the clamp State the obvious You've got to state the obvious sometimes to get marks The next one um and it's always helpful to have a diagram for this is to position the meter ruler so that it's clamped parallel to the spring So in line with the spring in the same direction You could do that with a set square but needs to be parallel Next you're going to view the spring from eye level What do I mean by that Well let's say you were doing the experiment You'd crouch down so that your eyes were exactly level with the bottom of the spring Then you'd use the ruler to measure the initial length of the spring Let's say you were told to go up in 2 Newtons You'd say add 2 Newtons to the end of the spring or 1 Newton or 5 kg or whatever it is Once you notice you add it you should be able to see the spring has extended downwards um so that it's gone past its initial length So what you need to do then is essentially repeat step three So at eye level measure the new length using the meter ruler Okay And then to find the extension how much it's gone up by you subtract those two measurements So stage three and five the final length minus the initial length and then put it in your table Now I've forgotten to mention here you want to repeat this with two newtons added each time to make sure you get a range of results Once you've got your results um you should be able to plot a graph This graph is quite a nice graph we should find um it gives a nice neat straight line So you got force our independent variable on the x-axis extension on the y a line of best fit should go um through the origin like so It can curve up a little bit at the end Um that just means it's gone past its elastic limit So what does it show us It's a straight line through the origin It shows us the two things are directly proportional Now we can also tell it's directly proportional from the table which is as one variable doubles 2 to 4 the other variable also doubles from 03 to 06 How do you make sure this experiment is accurate Well we want to make sure the clamp um has the ruler parallel to the spring to make sure um we get an accurate reading and we want to measure it at eye level Okay so that will be a control variable Do that every time Don't change it Independent and dependent variable quite straightforward here So force you change extension you measure Uh and safety use goggles and keep the stand in the middle of the table Newton's laws over 300 years old So what could be difficult about a practical involving Newton's second law Well let's find out Now the setup is key for this practical We've got a car on a slope and we've got something called a pulley which is um just guiding the string over the edge of the table Um and we have some masses and a mass hanger at the end Okay Now what we're going to try and do is using Newton's second law which is F= ma We are going to vary the force Now how we're going to do that is put masses on the end of the hanger Don't be confused We're not changing the mass where we are but we're using that to change the force How do we find the acceleration of the car This is a really tricky bit Okay So the definition for acceleration is change in velocity divide by time or rate of change of velocity So we got to find a way of measuring the time and the change in velocity before we can find our acceleration Now hopefully it's obvious that the one easy thing to measure there is the time We can use a stop clock for that or a stopwatch So we need one person with a stopwatch measuring the car's journey over the period of time Now to measure the velocity there will be some new equipment where this is really the only point that comes up in the GCSE Um use plenty A level um but they're called light gates Okay there's different types Uh they're essentially kind of like speed cameras Um they use lasers to measure the velocity of the car They can also be used to measure acceleration Um but uh we're going to use them to measure velocity here So these light gates measure the velocity at one point then at another point And we can find the change and divide that by the time to find the acceleration So how would a method look then So first things first we've got the car up the slope We are going to release the car from a fixed point on a slope So what are we measuring when it goes down the slope Well we're going to measure those two things the change in velocity and the time The time taken we can measure between two points using a stopwatch Then we're going to measure the change in velocity And that's where the light gates come in The light gates measure the change in velocity uh between those same two points between those two points on the slope That's worth noting here the light gates can be used to measure other things but in this version of the method it's to measure change in velocity Okay this is the easy bit cuz we've already got it written down We're going to use the equation acceleration equals change in velocity / time to calculate the acceleration Next um is we're going to vary the force So to do that we are adding masses to the end of the string from the car And then we repeat So we add another one another one and repeat Meth repeat parts one two three and four Now when I say from the car what I mean is uh the total mass of the system has to be constant So you take a mass off the car and you put it to the end of the mass hanger because otherwise you're changing the mass of the whole thing as well as the force which we don't want to do Okay So what kind of results are we expecting So let's say we vary the force in 0.1 Newtons each time We don't need much force here to change the acceleration Uh let's say we have these values for acceleration So if the mass is constant um what we'd expect to find is that the more force you add the more the acceleration Um and you'll get a nice straight line uh through the origin As one variable doubles the other doubles You can see force doubles acceleration pretty much doubles um meaning that magic two words they are in direct proportion with each other Okay Now there is another version of this practical um which doesn't involve direct proportionality which is slightly trickier um to do and trickier to ask about but we're going to obviously uh tackle it as well So if the force was constant on the car uh and the question asks you about how would the mass affect the acceleration what you would um do is instead of changing the mass on the pulley you change the mass on the car Okay So changing mass on the car making the car heavier and heavier and heavier each time not the force on the end Now um changing the mass you might be able to guess like with a lorry um it's harder to speed up or accelerate Okay So actually an increase in mass makes the acceleration decrease So like this in a curve Now this relationship um that special type of curve is called inversely proportion or inverse proportionality Okay So what it means is that one variable doubles the other halves So if I doubled the mass the acceleration would half Okay So you also find this in other parts of physics an inversely proportional relationship Now everything else about the practical is the same setup etc just what you're changing Okay accuracy um regardless of what the independent and dependent variables are um control variables are absolutely vital in this practical So you got to have the same slope angle uh for the whole practical You can't change the angle uh at all You've got to make the same distance between light gates as well otherwise um again it won't be a fair comparison Um don't say things like the car for control variables because it's kind of obvious you're going to keep the car the same throughout That's not going to change Uh for safety um have someone or something catching the car at the end uh the slope Um and that should be all that One of the trickiest practicals at GCSE is all about waves There are two parts to it One is water waves using a ripple tank Now you have a lamp above a tank of water um and a motor with a straight edge that makes ripples that go from one side to another Now the light's purpose is to shine light underneath um so you can see underneath the tank the ripples on a piece of paper below and you can measure them Now what we're going to measure about these waves is a couple of things You might see a question commonly asked how do you calculate the speed of the water waves in the ripple tank Now the absolute essence of this question is knowing how to use the equation wave speed equals frequency times by wavelength We're knowing what frequency is what wavelength is and how you can measure them in this instance So let's deal with one each of those things one at a time We're going to talk about frequency first So frequency we should know is the number of waves passing a point per second So how do we go about doing that Well we'll need a stopwatch because we need to know time to get the second element of our frequency Um so one person will have a stopwatch Um and one person will be counting essentially Now we're going to count the number of waves passing a point not in 1 second I'll talk about why in a second but passing a point in let's say 10 seconds Doesn't have to be 10 but needs to be a lot bigger than one Then we're going to divide that number by 10 to find out how many waves there are in 1 second Okay Helps with accuracy We'll talk more about that later So that's frequency Now wavelength Um we are going to do a similar thing apart from this time you need something different You need a ruler or a meter stick depending on how big your tank is um to measure the length of each wave Now again we're not going to do one wave because they are really small It's really difficult to measure for one wave Um and one thing to to go before this is in before you measure it you might want to take a photo That's kind of useful or a slow-mo video But either way we're going to use the ruler to measure the distance between 10 waves Um then divide by 10 Okay Makes it more accurate if we do it for a larger number then divide by what we need to find Now to find the speed you would then just quote the equation say multiply two numbers together in this equation uh to find the speed m/ second By doing multiple waves you are improving the accuracy of your experiment By measuring one wave you have things like um measurement error random errors from timers and you also have um you know one person can measure one wave incorrectly if it's very very small on a ruler So reducing the chances of errors Now one other method you could be asked to talk about it's kind of unusual but you could be asked to measure the speed using distance divide by time It's a similarish method You just measure the distance and time taken for individual waves to reach the end Now let's talk about the waves on the string then So uh on a string you have a vibration generator which as the name suggests vibr generates vibrations um across the string The waves then reach the end of the pulley and come back Now at certain frequencies you see these patterns start to form on the string Uh these kind of like waves or loops form on the string Now you usually have a little bridge or something there to uh kind of keep the fixed the length variable Okay Now while this looks like a complicated setup and it is kind of an A-level P um it is like easier than the whipple tank in lots of ways You get a similar question something like how do you calculate the speed of waves on the piece of string Now it's a similar answer to start off with We're going to use the equation I'm not even going to write it down again So frequency times wavelength But how do we know what the frequency and what the wavelength are So let's do them one at a time again um and see if we can spot any similarities So um let's talk about initially uh the frequency Now for this the frequency is very very straightforward So the generator will have a number on it or a dial like for example 12 which is too small for me to write here Um but it will have a number on it that will tell you the frequency at which the vibration dur vibration generator is going up and down at So up and down 10 times a second is going to be 10 hertz Okay Sometimes that's called a signal generator by the way Now the wavelength is the thing you have to measure So same as before we need a piece of equipment to measure it Usually it'll be a meter ruler here not a ruler but it could be a ruler um to measure the length of a wave Now what's important to notice here is that we're going to try and do multiple waves again Now depending on how many loops you've got on the piece of string um determines what the wavelength is But essentially if you measure um across several loops then you can essentially find the wavelength using the meter ruler Now what's important to notice here is that on my diagram that is one whole wavelength Okay Now one whole wavelength would be two loops So I've actually written here divide by number of loops Um and then you for two loops that's one wavelength Now to find the speed we just do frequency times wavelength Easy peasy same as before And the reason we do those several loops again is to improve accuracy Okay lots of measurements is better than just one measurement Another way to reduce the chance of errors um is how you measure the wavelength Um so quite a common thing in physics when you're measuring something with a ruler like the wavelength is to avoid parallax errors Um parallax error means not uh viewing something um like uh side on or perpendicular to or in line with Okay So viewing it a bit higher or a bit lower means the reading is different to what it should be which would be an example of a random error Um you could also miscount the number of loops um as well which would be an issue with this practical This practical is all to do with infrared radiation which is basically heat given off by objects above absolute zero Um there are two parts to it There's the emission of infrared radiation or giving it off Now we do this in two ways One with a Leslie cube which is a cube with different sides with different surfaces one black one white one metal etc Or you can do it with four or more separate containers with different surfaces that all hold water So first job is to get hot water um from a kettle and you fill up the cube or the cans with the boiling water If it's the cans they have to have the same volume How do we measure the infrared radiation There are two ways The easy way is using a thermometer Um because thermometer measures temperature which um can be an indicator of the heat released Way two is using a radiation detector Um usually in a question they'll give you a diagram to tell you which one to use So we're going to measure the temperature making sure we mention our equipment So using a thermometer or the radiation using the radiation detector So we're going to use a stopwatch to time um a period of time let's say 5 minutes for how long the uh practical is going to run for Then we're going to measure the temperature or the radiation again using the thermometer And the surface that has the biggest temperature difference i.e the highest becomes the lowest is going to be the biggest or kind of highest emitter of infrared radiation Now you should know out of all the surfaces the highest emitter we are expecting to be is going to be black uh in particular matte black which means that it is not shiny at all Sometimes you can see these results plotted on a graph So they all have the same initial temperature and they're going to go down at different rates depending on their surface of how their temperature varies over time And the one that has the uh kind of she steepest curve would be for example matte black the highest emitter the largest temperature drop Part two of this practical um is instead of emitting it's absorbing radiation Uh looks kind of similar Um so you'd have again four or more different cans with different surfaces um but the same volume Um and this time you'd fill them with equal volumes instead of boiling water Um because they're going to be absorbing radiation Um it just be room temperature or cold water Next you're going to have a heat source So that could be a lamp Um it could be anything really As long as it's an equal distance away from all four cans to make it a fair comparison um then it will work So you turn on the heater at equal distances We're going to measure the temperature using a thermometer Okay So this one you wouldn't really find with a radiation detector So you're going to record the temperature at the start and then you're going to again time it after 5 minutes and measure the temperature here Now I missed out a slight step here which would be to measure the temperature at the start or ensure it's the same temperature which would be something to put in as well Now again you look at the surface with the biggest change in temperature this time is an increase because it's absorbing radiation Um so the biggest temperature increase would be the biggest or the highest or best absorber of infrared radiation So the one that takes in the most and again we should find that's matte black It should be the best emitter as well as being the best absorber Let's talk about variables So this is a good experiment for independent variables This is what we change These are the surface or the material or color The dependent variable is what we measure So that's going to be temperature or infrared radiation uh depending if you're measuring that instead Control variables for this practical We want to make sure we've got the same volume of water in each can Uh they start at the same initial temperature Uh if we're using a detector it's got to be the same distance away from each can And if any of these are not kept the same that would be an example of a random error if you just missed out one of these things for the odd reading This practical comes up a lot It's a separate science only practical It's to do with reflection and refraction Let's do reflection first Now reflection involves a mirror The first thing we're going to do is have our ray box set up close to our mirror and we're going to draw around the mirror on a piece of paper Next we are going to use a protractor protractor to draw a normal line The normal line on the mirror that is 90° to the surface So let's draw on what that would look like Step three you're again going to shine the ray box or shine the light Let's start say an angle of 20° between the ray box and the normal So let me show you on the diagram what that looks like Um obviously measure with a protractor Again um the angle would be between the ray and the normal I know that angle is not 20 but let's assume it is Now that's our angle of incidence If you get a table um with results in draw X's where the ray of light goes uh so along the beam of light and that's where it enters and also where it leaves the mirror So we draw X's and then you take away the equipment and you essentially join the uh lines up So you remove the mirror and you join up or trace the rays um through the X's Okay Lastly measure the angle of reflection So that's this angle here on the diagram So that's between the ray of reflection and the normal Now we should find is those two angles are equal um which uh you know obviously it won't be exactly equal because there always measurement error there's random errors as well Now the slightly more common version of this practical to come up is to do with refraction Now all I'm going to do is I'm just going to edit this method um just to bear in mind it's for refraction instead of reflection So for refraction um instead of a mirror we have got a glass block or a perspects block We've still got a ray box that's shining light in um but this time we're going to see how it behaves when it goes through the perspects block or the glass block So we're going to replace the word mirror with our um perspects block on paper We're still going to do a normal line So let's um kind of draw that on on our diagram Um and we are going to still shine the ray box in at an angle of 20 degrees to that normal So let's draw my normal on um 90° with my protractor Then the ray goes in You measure the angle of incidence and you shine the ray box in at that angle Okay Now next we should know that the ray goes through the box at an angle and comes out at an angle But we don't know that because we have the block in the way So the really important for this method is you mention those X's or those crosses you draw along the the incident ray and this time it's the refracted ray coming out Then you take off the block stage five and you trace in those missing rays That then allows you to measure the angle R Now for this practical uh the angle of instance is always going to be bigger than the angle of refraction rather than being the same You can see those two angles there I is always bigger than R Now for both experiments you want to make sure you repeat for different angles depending on which ones they give you So in my example you'd say repeat for 30 40 50 etc however many results they tell you about Often they give you a table results and ask you how you'd find that out Pling a graph for the refraction practical This isn't going to be a straight line and this will curve So be prepared to draw a curved line of best fit for this practical Should be a smooth curve just one line going from the origin between as many points as you can uh don't make it sketchy Um this is for the reflection uh graph though you should find that the two angles are equal So they would be uh directly proportional because it's straight line going through the origin and whereas one doubles the other doubles Often gets asked in questions about these sorts of practicals are sources of inaccuracy Where might you have inaccuracies So uh the big one is that the width of the beam from the ray box If you've ever used these and they can be quite thick They're not actually that thin especially when you're using a protractor So it can be too wide which means it's difficult to see or to measure where the center of the beam is Safety wise um the ray box is the big issue here Um it gets hot so you want to leave it off between readings or don't have it too high a voltage or um uh yeah leave time to cool before touching it at the end of the practical Uh that kind of thing would be the essentials to talk about there And there are all the required practicals for GCSE physics paper 2 Please leave a video a like if you enjoyed it and make sure to revise them uh for the exam