AQA Physics Paper 2 2021 Higher Walkthrough

here we come to the last paper of signs that we're going to do at least for this year and this is physics which is my my jam that's my stuff okay I love physics that's what my degree is in I am a big fan of it absolutely although I understand why a lot of people hate it completely understand too but hopefully I actually think that I could do the best explanations for this subject because I find that it's not just conceptually kind of knowing stuff you have to actually understand it in order to answer some Physics questions it's not all memory which is why you know I feel like I'm gonna be a bit more useful on this but without further Ado let's just get straight into it again the link to the paper is going to be in the description in case you want to follow along or use this as a mark scheme or whatever you want to do here we have to figure one showing a stretched spring and the spring is elastically deformed because we're having hanging a mass from it so I'm thinking like hooke's law I'm thinking about those kinds of things and it says here what is meant by elastically deformed so this is basically just one of your definitions that you're going to do so remember elastically deformed is whenever you have something that's stretchy and you stretch it you change its shape by doing that so in this case it says as the force on the spring in case it's the length of the spring increases that's Hook's law that's not elastically deformed only a very false so let's actually cross these off as we go along only a very small forces need to stretch the spring uh the Frozen spring caused it to change shape it could be that maybe the spring will return to its original length when the force is removed so there's two different types of deformation we talk about we talk about well technically a few others but we could talk about plastically deformed and elastically deformed technically you have permanently deformed but let's leave that the key thing about elastic think about an elastic band when you apply a force if you were to let go it returns to its original shape that's one elastic thing is a plastic thing I can deform it but it won't spring back to its original shape so for example if I get a kind of maybe a can right like a can of Coke or whatever I can crush it and plastically deform it but it's not elastically deformed because when I Let Go it doesn't ping back into the shape of a can does it so other things I like elastically performed mainly things like Springs okay or anything with some kind of Bounce to it so like a rubber ball is also a pretty good one to use so in this case it's going to be the last one the spring will return to its original length when the force is removed four parts so it says describe a method to determine the extension of the spring so if you're lucky you've done this experiment in school already but the way you determine extension if you think about this kind of setup right we have this original spring right and then afterwards when we hang a mass its length changes okay so we can't measure that extension easily directly but what we can do is measure the length of the original spring so measure the original length measure the new length so let's just call it you know Ln for new length the difference in these two values is going to be my extension so that's why you have the ruler hanging up next to the spring you take the original length you then hang a mass on it write down the new length and then take the difference between them so how do we write that in words so you can get the four marks well the first thing is you measure the original length of the spring measure original length of spring and then measure the length after so measure you can call it the extended length measure I don't know why but there's like an e button on my graphical pencil I really don't know why but anyways measure the extended length length and subtract original length length to get extension to part three it says the extension of the spring is 80 millimeters the spring constant is 40 Newtons per meter calculate the elastic potential energy of the spring use the physics equation sheet for three marks this is a lot of marks a question that's not too bad the equation that you're looking for is that energy is equal to a half times the spring constant times the extension squared which is sometimes given as an e or it can be given as a Delta X instead either way is completely fine so subbing those numbers a half then it's 40 and then what about extension well if you look at my spring constant it's Newtons per meter so you need to make sure your extension is in meters so how do you do that well how many millimeters are in centimeters how many millimeters are in a centimeter there's 10 so divide by 10 gives you 8 centimeters and then how many centimeters are in a meter a hundred so divide by 100 you get 0.08 meters so let's put that all in whoops don't forget the other zero squared and then let's type it all into our calculator so instead of a half I can put 0.5 but let's just do a half times 40 times 0.08 that gives me an answer of 0.128 joules which is a very small amount but that should hopefully make sense because there's not much going on with this in the next question it says write down the equation which links extension e force and spring constant this is Hook's law so that is going to be f is equal to ke again sometimes they use x for extension instead but whatever they use it's all the same thing okay so it's just hooks law and for part five it says a force of 300 Newtons acts on a different spring and it extends by 0.4 meters calculate the spring constant so all we're trying to do here is using this equation at the top so f equals ke to work out K so you can use it as a formula triangle if you'd like so let's do a little triangle that'd be f k e if we're covering up k then it's going to be force over extension or if you're a bit more mathematically inclined you can just rearrange this formula by dividing both sides by e but either way the way you're going to do it is you're going to take the Force 300 and you're going to divide by 0.4 and that's for three marks like that's not bad at all so 300 divided by 0.4 gives me 750. now of course you need to remember the units but in this question in particular they've given them to you so it's even easier three marks in my opinion not that bad the rearranging is obviously the part that's a bit tricky and yeah if you with this question if it's on your formula sheet then you can just use that of course so just keep that in mind be open to reading that formula sheet question two we have professional rugby players where a tracking device that measures the velocity and acceleration figure two shows a player wearing a tracking device so right here apparently the players tackling another players Running With The Ball velocity and acceleration are both Vector quantities what is a vector so is it a quantity of both magnitude and Direction only direction or only magnitude so first of all this is none that is not a vector or a scalar the only question is whether or not it has direction or not okay so scalars are only size so they are only magnitude so things like time right when I say like one hour I don't give you a direction do I I just say one hour when I say how much I weigh or how much mass I have if I said 80 kilos I'm not giving you a Direction with that if I give you my speed 50 miles an hour there's no Direction you can't tell which way I'm going you just know how fast I'm going or how heavy I am okay well how much time it took with a vector quantity it has magnitude and Direction so for example if for me to change my speed to Velocity so when I said 50 miles an hour if I said 50 miles an hour heading west that is now a velocity because you can tell which direction I'm going in okay with the mass while tending to have weight which is a force forces always have directions right weight always points down that is a direction or you could have something like friction that goes opposite to wherever you're moving that's a Direction but that's the general idea okay so just think about whatever quantity you have if it has the direction if it does it's Vector if it doesn't it's a scalar this is for part two which of the following is a vector quantity so let's go through them one by one so displacement displacement and distance are effectively scalar and Vector forms of each other okay now displacement is distance in a given Direction okay that's the key thing so the example I like to use is Imagine This Is Me as you can see one-to-one recollection although I haven't got the hair right of course and let's say I walk this way and then back now let's say that distance is one meter the distance I've traveled is two meters right one meter to the right and one meter back to the left but what's my displacement well displacement is distance in a given Direction it is the total dis how far away you are from your starting point so I've gone one meter away and then one meter back how far away am I from these starting point zero meters okay so displacement is a vector whereas distance is a scalar it only gives a size okay now what about time well again it I don't have any metric for saying which direction I'm going in in time okay work done work done is the same as energy energy has no direction it's just a size I have a hundred joules of energy okay I don't say I have 100 joules going that way or going this way it doesn't make a difference now some of you might say but work done is force times distance doesn't that give me a direction no because distance is a scalar quantity okay so it doesn't actually give you a vector quantity okay so hopefully that makes a bit more sense with vectors and scalars just think about direction direction if there is a direction then you have a vector if there isn't a direction then you have a scalar so for the next two parts we have a velocity time graph and it's really important you make sure you know it's a velocity time graph for the player running with the ball and as you can see here it goes up then stays flat and then it goes down to zero so what is this describing well it's velocity so if velocity is increasing that means at this point the player is accelerating so she's speeding up when it's flat it doesn't mean she's stopped it means she's traveling at a constant velocity so she's reached let's say her Peak speed or velocity and she's maintaining it okay so again it's like going onto a Motorway if you've ever been in a car with your parents right as they go into the motorway you feel the acceleration you pull back because they're speeding up and then when they reach whatever speed so probably 70 miles an hour or 60 miles an hour they maintain that that is a flat line on a velocity time graph this bit at the end we can probably imagine what's happening if we go back to the original picture that's when I mean the players collide with each other right because all of a sudden in a very short space of time it looks like 0.2 seconds she's going from traveling at four meters per second to zero so slammed into each other which is pretty funny but anyways to determine the acceleration of the player so with a velocity time graph there's two things they can ask you to work out acceleration and distance traveled the distance traveled is velocity times time isn't it it's the area under the graph the acceleration its velocity divided by time so it's the gradient of the line so all you need to do is Mark off these two points so that's 1.6 so all we're doing here is we're taking the change in the y-axis again bit of maths so it ends up at four starts off at zero so it's four minus zero over ends up at 1.6 seconds starts at 0 so 1.6 minus zero so let's work this out so of course there's been minusing zero I don't have to worry about that I can just do fraction 4 over 1.6 but let's type it in fully just to make sure we're all on the same page 5 over 2 which is 2.5 meters per second squared does it give me my unit it does makes my life even easier so here it says describe the motion of the player between 3.4 and 3.6 seconds so what does that mean what does describe motion mean with the velocity time graph you're going to say this you're either going to say accelerating decelerating or constant velocity okay those are the three things you're going to say now with the accelerating and decelerating you need to say if it's constant or not so is the gradient constant I.E is it a straight line if it's a straight line going up that's constant acceleration if it's a flat line constant velocity if it's a straight line going down constant deceleration if it's curved you would just say not constant acceleration okay so in this case it's a straight line down so it's going to be constant deceleration hope that makes a bit of sense and here we have the force exerted on the player when she is tackled causes her to accelerate write down the equation which links acceleration a mass m result in force F this is your boy Isaac Newton's equations one of his Laws of Motion it is the second law of motion f equals m a if any of you doing a level maths or a level physics this is going to be your bread and butter this is going to come up a hell of a lot okay and in part six we get to use the equation how lucky for us so it says the player accelerator 25 meters per second squared when a result Falls of 1800 Newton's acts on her calculate the mass so again I'm going to draw out I mean first of all you could just rearrange the formula so m is equal to F divided by a but for those of you that like the formula triangles I know there's a few of you let's do it this way it'll be f M A we want Mass so it's force over area if you noticed in both parts you had you know for question one and question two we've had to rearrange this formula so again if you're unsure about rearranging now will be a really good time to just practice rearranging or writing up formula triangles for these kinds of equations Okay the reason I've written it like this is because m a i know that has to be on the bottom because that's where times is anyways so force over acceleration so we have one thousand eight hundred over 25 gives me again let's be nice and lazy 1800 divided by 25 gives me 72 kilograms again three marks hopefully not that bad and for the last part this is a bit of an interest like a nebulous question so they like to throw some of these in where they're not really related to science per se it's more about your ability to apply things to real world situations so it says the tracking device sends data to a computer during the game it's just an advantage of the data being sent during the game so yeah it's a bit bit tricky but think about what it means by centering the game it means that there is a live feed of data right so you can check the data during the game so check data during the game that's my kind of logic that I'll use doing the game okay you can also say things along the lines of it doesn't have to be downloaded afterwards or anything like that you don't have to wait until after the game to get information on the performance you can make changes during the game any of these also accepted for the next question we have a student makes water waves in a ripple tank describe how the frequency and wavelength of the water waves and the Ripple tank can be measured accurately so here we have two kind of components to our answer we're going to talk about the wavelength first and then we're going to talk about the frequencies let's start with wavelength now let's think about this actual experiment when you make waves in a ripple tank this is roughly your experimental setup so you're going to have something that's oscillating in a piece of water in a piece a body of water and what you want to do is you want to set up a ruler that is a horrible drawing good Lord you want to set up a ruler along the side of the tank like that and you have your ruler along like this and what you're going to do is measure the distance between two of these Peaks now what is this actually going to look like when you do the experiment because obviously you won't see this weird blue looking water well it looks something like this what you'll have is these dark patches and light patches so you need to do is measure the distance between two light or dark patches and this is literally where the water goes up and goes down because as you know the water is going to be traveling like this when there's a ripple and you can't see ripples so how exactly are you going to do this well what you want to do is actually set up a camera that's going to look down at this setup that you have here and you're gonna have the ruler along the side in order to measure the actual distance okay because of course this is actually happening in you know real time it's very hard to measure that in real time so instead you're going to use a camera to take a picture and then you're going to literally just measure the difference between these two spots so let's actually write out what we're going to what we're talking about here so all you want is you want to have a meter ruler ruler along the side of the tank you can also describe this as perpendicular to the actual wavefront itself but you don't need to leave you don't really need to say that and then what we're going to do is using a camera so take a top down picture and use the ruler to measure the distance and you can just call them between Peaks okay between pigs and that is your wavelength Lambda okay now what about for frequency well this is where it gets a bit more interesting there are a bunch of different ways to work out the frequency and again if you looked at the marketing for this question you might notice that my wavelength method isn't exactly what it says in the mark scheme but it is one of the alternative methods anyway so there are multiple different methods of doing this now for the frequency I like to think about what the frequency is the frequency simply tells you how many full wavelengths are going past each second so for example if I were to Mark a point here and count how many waves or how many Peaks go past this point every second that is my frequency and that's exactly what we're going to do to work out the frequency okay so again each Peak that passes this is going to increase the frequency so we need to do is count how many kind of go past it another thing you can do now of course to make it accurate we don't want to just do one second because imagine yourself with a stopwatch and you go you know tick tick that's you know it's very hard to keep track so you can either measure for 10 seconds how many waves go past that point and then divide the answer by 10 to get the frequency because in 10 seconds let's say you get 15 waves then you do 15 divided by 10 you get 1.5 Waves per second which is your frequency the other thing you can do is use this camera you set up earlier most cameras especially the ones using experiments have timers on them so you can literally just play it for a second in slow motion and count how many waves past that point either one of those is completely fine so I'm going to choose the latter option so play video in slow motion and count how many waves pass a given point that is your frequency so the question is where do you get the fourth Mark if I've already done three bullet points well it's some measure of maintaining accuracy so for example using video instead of a stopwatch is a way of maintaining accuracy so you can also mention things like taking photos of the setup so take photos to reduce uncertainty but that should give you the four marks and I hope that makes a bit more sense the student recorded values for the frequency and the wavelength of waves in the Ripple tank and table 1 and 2 are showing the results so we had the frequency in hertz and the wavelength in centimeters and it says determine the mean wave speed so what you want to do is get out your kind of formula sheet and locate the equation for mean wave speed and it is simply F Lambda you sometimes see it as written as C equals F Lambda either one's fine so we're just going to find the frequency multiplied by the wavelength now remember wave speed is in meters per second and I've noticed already that this is in centimeters so when we work out the mean we're also going to have to convert it into meters as opposed to centimeters so let's do the mean frequency so call it mean f how do you work out the mean that's a brilliant question well again if you remember some of your kind of GCSE maths knowledge you add them up and divide them by the number that you have so we're going to do 9.8 plus 9.4 plus 9.3 so 9.8 plus 9.4 plus 9.3 over three and that should give you an answer of 9.5 Hertz with the wavelength you're going to do the same thing whether you convert first or you convert afterwards shouldn't make any difference so 1.7 plus 2.2 plus 2.1 and then we'll change it into meters afterwards so if we add those all often divide them by 3 we get a nice even 2.0 centimeters Now how many centimeters are in a meter 100 so if I divide that by 100 you should get 0.02 meters which means last but not least you just need to now sub it into the formula we have back up there 9.5 multiplied by 0.02 gives you an answer of 0.19 meters per second again these calculations they're worth a lot of marks and they're not that bad so I would recommend once you get in the exam if you get stuck just try and work some stuff out okay try and work out means try and work out frequencies use any equation on the formula sheet to try and scrape together some marks because it's really easy to get marks okay questions might not be easy but you can gain some marks one is better than none part three this is testing your experimental knowledge what is the advantage of taking repeat readings and then calculating a mean and this is really important if any of you want to do any signs at a level or in the future you know in University or in a job every single human being on the planet that does science takes repeat readings and there's basically two reasons for this now one is the reason that they're kind of looking for which is it reduces the effect of random errors so reduces effect of random errors however there is another accepted answer so by the way with random errors what does that mean well random errors are ones you can't predict so if you do an experiment once how do you know you haven't had any random errors right so for example if you didn't know what a dice was at all and you rolled it once and the number three popped up if you draw a conclusion from that you would say okay every time I roll this dice I'll get a number three but how do you know instead the only way to actually verify that is to do it again and again and again and see what happens multiple times okay this is true for pretty much anything in life doing something once doesn't mean that it will happen every single time okay so reducing the effect of random errors you repeat and then you can compare the results so what's the other reason that you can use which they're talking about it also allows you to discard anomalous results how can you tell if a result's anomalous if you don't have other readings to compare it to you can't so either one of those answers perfectly fine but I wanted to also give you the knowledge of you know why that makes sense now here is actually one of my favorite styles of questions in physics because once you know the technique you don't need to know anything about science to get the marks so here it says the speed of the wave is affected by the depth of the water in the Ripple tank the deeper the wave sorry the water the faster the wave explain how the depth of the water affects the wavelength of the wave if the frequency is constant they've given you the answer in this question I'm not saying this to make you feel dumb I'm just going to show you a really interesting trick now physics is all about maths and interpreting it so it's all about equations so they're telling me the speed of the wave is faster in deeper water okay now what equation did we just use we used b equals F Lambda this isn't part of my answer by the way this is more like an explanation I'll show you the two bullet points that you need for the answer and they say that F doesn't change so somehow V is bigger despite the fact that F stays exactly the same what's the only possibility Lambda must be bigger it has to be because if f is the same but V is bigger Lambda must or wavelength must give you that extra bit so if I said the velocity doubles but the frequency is the exact same logically the wavelength must double because that's the only way the velocity could have increased so that's all you need to say and again we've used the equation right here and they've basically given you the answer the speed increases but the frequency is constant the only option is the wavelength increases so all you have to do is literally basically rewrite the question so you say deeper water increases the wavelength because as we've just discussed that is the only way for velocity to increase so deeper water increases wavelength which of course you can't just write Lambda unfortunately and then why because V increases and F is constant two marks and all I've really done is read the math read the equation and they told me all of the information I need to know deep water increases wavelength how do I know that well because V increases despite frequency being constant so Lambda must increase that's it okay hopefully that makes a bit more sense I hope so anyway but again if you have any questions leave them in the comments and I'll get back to you magnets everyone hates magnets and honestly I don't blame you they're very nebulous in fact I was in my fourth year at University by the time we actually got to learn about magnets in full so it's a very Advanced topic so it makes complete sense that you're a bit worried so figure four shows the magnetic field pattern around a permanent magnet where is the magnetic field of the magnet strongest you can either memorize this but I'm also going to explain it to you now it's at the poles so if you're okay with that feel free to skip to the next part but if you're not here's why when you have a field pattern whether it's gravitational electric or magnetic the closer together the lines the stronger the force okay in other words the more lines you have the stronger the force if I look at the poles there's one two three four five six seven eight nine ten eleven lines here if I look at these parts there's only three and three which means at the poles it's over twice as strong that's literally all it is that's why field patterns are so useful in science and you'll find this with electric gravitational and magnetic field lines the closer they are together or the more of them there are the stronger the force that's all you have to remember so you're just looking for wherever there's the most number of lines which is at the North and South Pole and part two basically piggybacks on what I just said how does figure four show that the strength of magnetic field is not the same in all places well as I just mentioned the closer together the lines the stronger the force these are not just equal distance can you see that they get further apart as you go away that's literally you need to say the distance between field lines field lines changes that's it figure five shows an electromagnet being used to separate ions still from non-magnetic materials explain one reason why an electromagnet is used instead of a permanent magnet now electromagnets are one of the most important inventions in recent history without them we wouldn't have things like speakers and microphones which use electromagnets to produce sound they literally vibrate a metal plate that's not sure how they work so why do we use an electromagnet instead of a permanent magnet the clue is kind of in the question permanent magnet electromagnet well given that there's a difference one of them can be turned off which is really useful a magnet that's always on it's not the most useful thing in the world because you know you sometimes want it to be off right like sometimes you want to take stuff off of the magnet for example so first one is that you can simply say the electromagnet can be switched off and again if you didn't know anything about science you could deduce this right why would they call one of them a permanent magnet and one of them an electromagnet well the electromagnet must be able to must not be permanent right it's not there's no point in calling it permanent if the other one is also permanent so one of them must be able to be switched off and it must be the electromagnet okay so again no science really involved so electromagnet can be turned off that's fine now let's think about why you would want a magnet to be turned off because if you look here it's trying to take Iron and Steel from non-magnetic material so why would we ever want to turn that off well okay let's just think have you ever used a permanent magnet and then you stuck something to it and then it's hard to get off right and you know I I you know growing up my dad had like really strong magnets I can't remember the reason why but every time I got stuck to like the radio or something it was hard to pull off well that's why we want to be able to turn it off is so that we can get rid of the metal that's attached to the electromagnet the whole point is to get the Iron and Steel out from this material so we can recycle it but could you imagine having to try and rip it off of the machine that just takes too much effort instead you can just turn it off it just drops it that's way easier so simply it's easier to remove the Iron and Steel or you can say the separated Metals by the way just FYI so I hope that makes a bit more sense at least one March I hope can be a bit logical I'm hoping I'm teaching you some exam technique here okay try and you know deduce it get your Sherlock Holmes on try and scrape together some extra marks because it's the difference between grades and this question is kind of common knowledge I'm afraid piece of iron is still attracted to electromagnet name two other metals that would be so the ones that you might be aware of are nickel and Cobalt which by the way is why things like you know the kind of bronze coins like the one and two P's are attracted to magnets it's because they're actually made out of nickel mostly hence they're magnetic but some other ones that you could say if you're a bit fancier uh and by these aren't in the mark scheme but what happens is when examiners get the mark scheme there's a certain understanding that they know enough about science to know some other kind of magnetic materials so you could also have Platinum neodymium is actually a pretty common one it's in um a lot of electronic devices you also have titanium and uh catalinium and also bismuth which is kind of interesting it doesn't sound like a metal does it but those are kind of the other ones you could have but these are the most common that you may have accomplished nickel I'm hoping you have anyways so in this part they say the design of the electromagnet cannot be changed so they're giving you a bit of a restriction here give two ways the force exerted by the electromagnet on a piece of iron or still could be increased so if they gave you full grain you might say something like you know give it a soft iron core wrap more coils around the electromagnet something along those lines but they're saying the design cannot be changed so what else can you do well the other two things it's affected by the first one is increase the current now in this actual exam the second one was very difficult because it's not in textbooks okay so again other things soft iron core Etc you know all of those standard ones but they're saying the design cannot be changed so the other one was a lot trickier for people to uh to kind of come up with now as with all forces magnet magnetism gets weaker with a distance so this probably makes sense now if you ever thought about using a magnet it doesn't attract everything from everywhere you have to bring it closer and closer until the object starts to move towards it right because with distance the force gets weaker so simply move the electromagnet closer to the iron or Steel in my opinion it's a bit of a cheat Mark but you know a lot of people didn't did not get the second Mark at all but hopefully it makes sense now again think outside the box and certain questions okay here we have the motor effect or the generate effect simple motor you've probably seen this before but you're probably starting to panic now because this gets a bit tricky and if we go down we have a five Mark calculation however I want to point out it's not that bad of course if you're struggling with magnetism it is bad but think carefully they've given you I write down the names of the variables so they give me length they've given me current and they've given me Force so what I would look at on my kind of formula sheet is look for an equation that has f i and L in it and if you're kind of on it hopefully you know that magnetic flux density is B so you're looking for an equation which has f i b l in it and there's only one on your formula sheet in fact there's only one for f i l I'm pretty sure so you should find Force equals bill and then you're just subbing in the numbers they give you but again put it in standard units so millimeters is no good we need to change it into meters so all we have here is the force is 0.36 magnetic flux density is what we want current is 4 and 120 millimeters in meters is 0.12 and then all you need to do is if we sort of start 0.36 equals 4 times 0.12 is 0.48 B so then B is just equal to 0.36 over 0.48 which would give you 0.75 and then the unit which is another Mark so you actually get a mark for the answer and a mark for the unit and then it's three markers for this in terms of maths it's really not that bad but again if you're confused if you're scared because of all these other science words just write down the variable letters and then look on your formula sheet it's it's your best friend in this exam okay five marks is a huge amount for a relatively easy calculation that you have a calculator for anyway okay I'm not trying to put you down I'm trying to say use that formula sheet to work out which equation they want you to use even if I remember once I went into a science exam and I didn't know what the hell they were talking about in one of the questions and I used this is one of my mocks by though not my final exams but I used the formula sheet they gave me and worked out the equation and got the answer right okay it was pure guesswork I was very good at kind of being lazy as you guys can probably tell but hopefully that makes a bit more sense here we have the good old-fashioned Fleming's left hand rule which is why people start throwing up gang signs in their science exams and we just need to complete the figure we don't actually have to use it which is kind of nice now how do you remember which one's which um practice but obviously that's not very useful a couple days before the exam so what I do is I think of what the fingers are called so I'm going to try and show all my fingers this is called my first finger first finger field so it's the direction of the field what kind of field is it though it's a magnetic field so again first finger field so first finger field that's how I remember that one now what about this middle finger well it doesn't begin with m it's also my second finger do you see the C in second so second finger is current now what about the thumb this one isn't going to make much sense to you guys uh it might do to a few people who've been taught by physics teachers like my physics teachers but the thumb is th right if you underline that that stands for thrust which is the same as Force so yeah how about for those of you that don't use this weird way of remembering it how else can you remember it well if you know that there's field and current for First Finger current second finger sorry first finger field second finger current the other thing is just the force okay I don't know if that really helps but at least for those two hopefully it does but yeah that's essentially how I remember it other than just practice and a lifetime of doing physics here we move on to the radiation slash visible light thingy part of your spec so different parts of electromagnetic spectrum are used in medical imaging so here we have an image of a person's hand with an infrared camera which measures shockingly infrared radiation which is associated with heat to help so how hot and cold different parts are so as you can see here so by the way just as like a behind the scenes when you see something like this the hot parts are actually good because that means there's a lot of blood flow this person here has lack of blood flow to his two fingers here and you can tell that because if you look this is about 23 degrees these are 34 degrees 11 degrees hotter so that's really not good the problem person probably has lost circulation in two fingers completely anyways so explain why the infrared camera is able to show that parts of the hand are at different temperatures well again I mentioned before that infrared radiation is associated with heat the hotter something is the more infrared radiation it gives off okay that's pretty much the basis of our answer now so different so different temperatures emit different intensities of infrared radiation so of ir and this is represented as different shades cool that's it part two infrared has a radiation oh sorry a range of wavelengths from 700 nanometers to one millimeter which part of the electromagnetic spectrum would have waves with a wavelength of 6.5 times 10 to the minus 7 meters so you might notice that this is actually 650 nanometers the reason why I say that is it's very close to infrared radiation but it's a slightly shorter wavelength so all you need to think about is on your kind of electromagnetic spectrum which one is just a shorter wavelength and infrared is actually visible light generally if you have a times 10 to the minus 7 and it's below 7 times 10 to the minus seven it's going to be visible light okay so hopefully that makes sense for part three we have x-rays and gamma rays being used for medical imaging so we have an x-ray here gamma ray over here choose x-rays for medical imaging a machine produces a very brief burst of X-ray so it doesn't last very long choose gamma rays a radioactive eye step is injected into the patient's blood the eye step is circulated around the body and the eye step is continuously emitting gamma rays compare the potential risks to a patient of using X-rays and gamma rays for medical imaging so as you may be aware if you've ever had to get an x-ray X-rays and gamma rays are both dangerous so that's exactly what we're going to say so x-rays and gamma rays now when I say it's dangerous why is it dangerous right it's only an x-ray right you can't even see it well the reason is is it's ionizing radiation which means as it penetrates your body it's going to start ionizing bits of your DNA which can cause mutations which is basically what cancer is so X-rays and gamma rays have a risk of cancer so they both have that risk now the question is which is kind of worse x-rays or gamma rays well if we actually look they've given us a little bit of information first of all very brief burst of x-rays that implies it's very quick whereas with the gamma rays it doesn't say it's brief in fact it says the isotope is circulating around your body you can imagine that it takes longer than just a flash if you've ever had an x-ray it literally is like taking a picture it's very very quick so all we have to say is x-rays have a shorter exposure than gamma rays so that means it's like a lower risk in that sense and what was the other thing I said well with an x-ray they generally only take a picture of part of your body maybe your leg maybe your chest area or something like that with gamma rays it goes around the entire body which means you're being irradiated through your entire body so gamma rays spread through or irradiate it radiates your entire body whereas x-rays irradiates a small part that's it four marks not too bad I will say that you can kind of extract this information from the text if you read quite carefully but again some real life knowledge and obviously that handy cgp book has probably helped you out with that one x-rays are produced by colliding high energy electrons into a metal Target the electrons have high energy because they accelerated to high speeds only a small proportion of the kinetic energy of an electron is converted into an x-ray when it collides with the metal Target an electron is accelerated a distance of 15 millimeters and the work done is 1.2 times 10 to the minus 13 calculate the fourth so again what we're going to do is going to label d this is work done so w and the force is obviously F so you're looking for an equation that has f w and D in it and hopefully you come across the work done formula which is work done is equal to force times distance and we're trying to work out Force so that would be work done over distance so work done is 1.2 times 10 to the minus 13 joules and what about the distance well it's 15 millimeters so if we divide that by a thousand we should get kind of the value that we want which is 0.015 so divide that whoops that damn e button zero one five and let's whip out our calculator we have 1.2 times 10 to the power of negative 13 over 0.015 excuse me value of 8 times 10 to the minus 12. Newtons that's it so in the previous part I mentioned that they use tungsten as the metal for the Target now tungsten has the highest melting point of any metal so why would we why would using tungsten enable the x-ray machine to be more powerful well this comes from the fact that as you collide with things you produce heat so if you kept punching a wall you would eventually start heating up the wall itself every Collision transfers kinetic energy and kinetic energy is heat energy so enables the machine to be more powerful so what they mean by that is you have more energetic x-rays right which means you need to slam those electrons into the metal Target harder and harder and harder now if your metal has a low melting point the metal will begin to melt the target will melt and it will be damaged so that means the machine won't work so that's why if you use tungsten you'll have a very powerful machine because it can withstand those collisions so electrons colliding with Target cause Heating cause eating which increases the temperature and so you need to have a metal with a high melting point so a high melting point allows more energetic collisions collisions this question I'm actually going to write the answer along the side because I think it'll make my handwriting a bit easier if I'm not actually using my handwriting but scientists are developing a Hypersonic airplane so fast on the speed of sound now travel much faster than normal airplanes an airplane accelerates from a low speed to a high speed with the engines at maximum power but why is the acceleration not constant so this is a really good question so when you have the engines at maximum power right at the beginning I'm going to draw a plane as just a box there is just the forward force of the engine and that's like right at the beginning however as this object This Plane starts to speed up it's hitting the air with more Force which means there's more air resistance so this air resistance which is this way I'm going to call it FR begins to get bigger and bigger and bigger and bigger now what that means is the actual resultant Force the overall force is changing and remember resultant force is equal to mass times acceleration so if there's a resultant force it means there's an acceleration so all we have to do is the forward force is constant right that engine force is always going to be constant however as the plane accelerates the air resistance increases the resultant Force is equal to the forward Force minus whoops air resistance so over time or over time resultant Force decreases f equals m a so the acceleration decreases that's exactly how I'd write it so it's not really that many words so just go over again right at the beginning as soon as the engine turns on you have this massive force from the engine pushing the plane forward however as this plane speeds up air resistance gets bigger and bigger and bigger now the resultant force is just the difference between those two forces so you take this forward force and you subtract this resistive Force the air resistance now because the air resistance is getting bigger the resultant force is getting smaller which means the acceleration is changing over time so hopefully that makes a bit of sense so always relate things back to kind of f equals n a when you talk about forces here we go so we have a Hypersonic airplane that has six engines sorry jet engines I've read the marks so we have six marks in total jet engines and a rocket engine now the speed of airplanes is tends to be used as the Mark scale in terms of speed and it literally is just how many times the speed of sound you're going so Mach 1 is the speed of sound Mach 2 is twice the speed of sound and so on the jet engines will accelerate the airplane to Mach 5.5 the rocket engine will go from Mach 5.5 to 25.5 in 300 seconds the average resultant force is going to be 630 000 Newtons calculate the mass give your answer to two significant figures well I remember what I said f equals m a is what we're going to be using for this equation because if you ever have force and acceleration and you want Mass that's f m and a so using f equals m a okay so it's always going to be the same now what do we have well we have the force the force is 630 000 Newtons the mass is what we want to work out so we don't have that yet and the acceleration we don't have so we're kind of screwed however think about it what is acceleration it's the change in velocity over time so it's the change in velocity so all we need to do is use this as our change in velocity now keep in mind that we probably want to actually work this out in terms of meters per second so V minus U is just 25.5 minus 5.5 which is 20 or mach 20 I should write but 20 Mark is what I want to have now to change that into meters per second which is what we want we do 20 times 330 which is going to be 6600 meters per second to add on a zero and double it so the acceleration now is going to be 6600 over 300 seconds okay to cancel those out that gives us 22 meters per second squared okay so now we have f equals n a we have F and we have a so we need to rearrange that formula again if you want to use the formula triangle let's draw it out for you and we're going to have gold that's absolutely terrible F on top we have M on the bottom and a cover up the mass and we're just doing Force divided by acceleration or if you want to rearrange it just divide both sides by a so we're just doing mass is equal to force over acceleration so 630 000 over 22 so get out your calculators so boom here we go six three zero one two three over twenty two gives me two significant figures so we have I'm gonna write out the full number first well I'm not gonna write the decimal points because I'm lazy kg then it's two significant figures you go to the second number along so one two underline it look at the number next to it if it's five or bigger you round up you make the number we underlined one bigger and then you just replace everything with zero so 29 000 kilograms to two Sig fig and that brings us to the end of the paper and the end of most of your gcses so mostly you're gonna be finished off to Friday after the physics exam however I know some of you have like food Tech and further maths things like that but yeah best of luck with the exam again in the comments leave any questions you have and I'll get back to you I love physics it's my jam I can talk about it all day but yeah I hope this was helpful and best of luck