Year 10 Revision Part 2

Right. Hello, year 10. Um, first of all, I will apologize to everyone for having to listen to my voice. I'm sure you're all sort of either at home revising and do without it. However, I did promise that I would go through the second half of your year 10 mock revision list um as we didn't get an opportunity really to go through it in class. Um, so um if you find this video useful, you are more than welcome to obviously sit through it and persevere. Um, there will be no floaty heads of mine floating around the screen. I'm sure you'll all be pleased to know of.

Um, this is not designed to be a video with any great finesse. There will be no, um, high-grade video editing. Um, I'm literally just gone for it once. Um, couple of bits I've I've just sort of chopped in to make it shorter and fast as possible. Uh, but it's I don't know about 30 or 40 minutes in total. So, hopefully if you'll find this useful, uh, please do sit down, go through it. Um, I'm trying to pick on the key points and the sort of things that will come up on your exam. However, I will not be offended. If not, you're welcome to use your revision guide. Just please make sure you're doing a uh a a decent amount of revision and a purposeful amount of revision. So, this will be more supplementary than anything, but hopefully I'll be able to touch upon some of the points that you might come up on your exam. Hint hint.

Right. So, moving on. So, what I won't be going through, I will not be going through the forces topics. Um, and that's because we went through these in class, but obviously there's there's the core practical the F= MA one. There's also a little bit on speed time graphs, uh, distance sign graphs, but there's a big bit on momentum as you can see, quite a few points in there. So, please make sure you are up to date with momentum. We've obviously got the energy bits, GPK calculations, pretty straightforward, and obviously the efficiency calculation along with drawing samps.

Now the bit I intend to go through in this and I've already made the video so this is just a bit of a intro um is the waves topic. I'm going to ignore EMS the electromagnetic spectrum because there there's little on the test for it and we've just covered it. So what we will go through you should be quite up to date with anyway and that just obviously adds um some more time onto a very busy schedule which I'm sure you all have. So um so I'm going to go through what the following topics on here particularly focusing on things like uh total internal reflection refraction practical which you call practical uh measuring wave speeds there obviously two ways to do it again I call practical and obviously look at how waves interact with different surfaces alongside of that looking at the speed of sound and calculate speed of sound as well as infrasound ultrasound and then finally go on to the uses of those infrasound ultrasound and leaning into earthquakes including S&P waves waves, just a reminder, primary and secondary wave, which we'll look at later.

So, without further ado, get straight into it. I probably made a few mistakes along the way. Um, so don't judge me. If I really wanted to uh make a perfect video, I'd put maybe hours and hours into it. I'm literally having a run through hopefully one and done. Um, probably with a couple of trims as I have a quick look through the whole thing and change sections. But anyway, persevere with me. I'll start off with wave speed. Again, apologize about the writing. Um, but I'm sure you're used to it by now. I'm never going to be uh into calligraphy of any regards, but I'll try my best. You try your best. I'll do the same.

Right. So, first things first then, calculating wave speed. There are two ways we can work out wave speed. And I'll just do a little line just to separate them. One of the ways we can work out wave speed is simply by doing speed equals distance over time. Now in the exam which you've done more recently I did actually spend quite a bit of time on this because there were some silly marks that people messed missed out or just didn't go through and fully explain what they were doing. They were just assuming uh me as a marker or this examiner was actually understanding what you were getting at. You have to be explicit. You have to explain clearly and thoroughly um how you're going to take these measurements including equipment. So, for example, if you're taking the speed of a wave, and I'll just draw a little wave. This is a wave that's say a tsunami. It's going to fire through some water. Of course, my pen is running out. Hopefully, that will not run out so I don't have to run off. Um, but if a wave travels through water, a very simple way you can just say is to measure the speed, you can just take a distance. Now, that if you actually want to increase that, you can say take a distance between point A and point B or I can say take displacement. Remember distance in a direction is displacement. Um, so I can take a distance let's say 10 meters. Now the bits where people are missing out of course and it's quite annoying that this is rocking. Can I uh resolve that? Um, you'll just have to make do for the minute. I'll sort it out in a minute. Um, so uh take a distance. Now a key bit is you have to state what you're taking a distance with. Don't just presume that the person who is marking it is just going to assume you are going to use a tape measure. You will lose marks if you do not state you are using a tape measure for this. So just be aware of that when you are saying taking measurements. Please make sure that you are stating you are using the the equipment or the apparatus to measure it with. So in this case obviously a distance taken a tape measure and time is obviously in uh seconds and we obviously use a stopwatch. So very simply if you're going to explain this thoroughly measure the distance that a wave travels from point A to point B or two points you can measure that out using a tape measure and you could use a stopwatch to measure how long it takes. Once you've got the time, let's say it's 10 meters and the time is 20 seconds. It's just simple 10 divided by 20, which is distance over time to equal our speed, which is obviously 0.5 m/s.

So, very straightforward for that one. Um, just a couple of things. They may say, how can you get more accurate results or how can you make more reliable results? There is actually a difference between the two. Reliability is the how can you rely on your results? Well, if you've done it several times and work out an average, even if one of them was taken incorrectly or a little bit off, you can actually work out a mean average. Now, you've got to state the following. You need to state calculate a mean average. You need to um repeat the experiment ideally three times or more and then work out a mean average as a result. So, you have to state the whole thing to get the marks for that. Accuracy is a bit different. Accuracy relies very much on um the skill of the person taking the measurement in some regards or the precision of a a device and being able to take it at the precise time that is again precision falls in a different sort of circumstance because that will work out to sort of decimal places but um so um I I'll steer away from that but just going through the first one speed equals distance over time and moving on from that we've obviously got velocity now velocity and speed obviously the Same thing. This is just assuming in a direction. So it could have very much just chose V for this. Um, but when you assume direction, I'll write it down. V = X * T. Uh, because that's got a direction. X actually is distance with a direction which is actually displacement. So you can say velocity is displacement over time and speed equals distance over time. Essentially they are the same thing.

The other way obviously that we mentioned the other um the other way of measuring wave speed or wave velocity is by doing frequency sorry times the wavelength. So frequency times wavelength very simply you need to measure them both. So to find the frequency um you first of all need to state that you need to count the number of waves in the given amount of time. Now a nice way of doing that is if you calculate the number of waves in 10 seconds that pass a point. So let's say there are 10 waves that you count that pass a point and you measure that and that's over 10 seconds or let's say it's in 20 seconds just so we get something other than one. So our result there are 10 waves that pass a point over 20 seconds. Now I've stated count the number of waves in a given amount of time. Now I've given the amount of time and therefore 10 divided by 20 will give us 0.5 hertz. Now hertz is just measuring the number of waves per second. So waves to work out the frequency it's just simply measure the number of waves in a given amount of time and divide the number of waves by that time and that gives us 0.5 htz which tells us how many waves pass a point the second which is obviously in this case a half. Now again explaining that clearly measure the number of waves state the given amount of time ideally using a stop clock to measure that amount of timing. Uh when we're going then onto uh the wavelength the wavelength is obviously just for those who need reminding it's from the peak to peak of a wave or any point to another point in the wave. So trop to drop in this case. Now to do this you need to use a ruler. Um, so let's say here is a ruler. Um, and if I'm able to freeze those moving waves by using a camera, I can then obviously measure from one point to another point. Let's say that's between A and B by placing it under it. Obviously, now the ripple tank actually does this. They can use a strobe which basically makes the the waves look still. And how it does it uses a flashing light the same frequency which the waves are vibrating. It makes them look still. But in in our case, just put a ruler on, take a camera phone out or whatever, and just take a picture. Uh, and therefore, you're able to measure two points. Once you've done that, you then need to take the final step. Say you need to measure your frequency. So, your number of waves per session uh per second times the wavelength, which you've measured using a ruler. Remember, stating apparatus. Um, and obviously that will give you a set amount. So, let's just say it was 2 meters. So two times a half in this case or half times two if I'm doing it the same way as that half times two would equal one obviously. So and that will tell us it's 1 m/s.

So, just two different ways to measure the wave speed nice and easy easy to do straightforward but it's when you're actually describing those practicals being able to describe it thoroughly. Um, now you might get a comparison of each well one which is best as long as you justify it it's quite easy but you might say it's hard to measure the wavelength because the waves are moving and therefore this is an easier way to perform that practical as an example for that right.

Now uh moving on from that then I'm just having a quick look um it says uh transmission absorption and reflection of waves now I'll I'll move on to a different page uh just going go through um reflection. You should know the law of reflection, but I'll give you some examples. So, a wave goes into a surface and it will it will bounce off from that surface. Um, as such, now a couple of things that you need to remember. Remember to draw your arrows. Miss arrows miss marks. Very simple. Obviously, I'll finish off drawing up my mirror. Now this is a plane mirror which means it's flat just on a flat plane. Um, now in this case you should remember this is our incident ray and this is our reflected ray and therefore this is the angle of reflection and this is the angle of incidence. Now this is always the case the angle of incidence is always equal to the angle of reflection um of incidence is equal to angle of reflection. Now you obviously don't put AOI. You need to actually write it down. But the instant angle is always equal to the angle of reflection. Now they might give a a case where a ray of light hits a curve mirror for example whether it curves in or out. But if you get really close to it and put a straight line on there effectively when you get to the surface is flat. So therefore it will bounce uh it will bounce um at the same angle it goes in at from the normal line. And just a reminder, the normal line, which is we've spent quite a lot of time on, is perpendicular to the surface or at 90 degrees from the surface. And we always measure from the normal. So they'll try and catch you out with a random angle here. Let's call it A. And they'll say, what will the reflective angle be? And they'll might give you a value for that. So let's say 40. So people jump to the other side and say, oh, it must be 40. When obviously um you have to work out what this angle is, which should be 50 degrees. Obviously take 40 away from 90. So, um, couple of examples on there, but law of reflection, angle of incidence is always equal to the angle of reflection.

Right, of course, my pen's running out. Right, moving on from that. U, let's have a quick look at refraction. Uh, because it asks you to go and look at refraction. So, just as a quick reminder, light waves can do several things. They can reflect off a surface or they can transmit through a surface or finally they can be absorbed by the surface. Now, if they're absorbed, the object's gaining energy and therefore will probably heat up. Uh, if it reflects off, it just bounces off and and I'll do it in this case. In fact, I'll turn my little paper over. In this case, it's going to transmit through or refract through. Now, this is sometimes called the infraspace where the light hits a different medium or a different surface. Now, as a quick reminder, light when it hits a different surface, uh, it doesn't speed up, it actually slows down and it's related to the density of the particles. So if I you imagine if I draw two little boxes, light is traveling. Here are some particles. Let's say this is air. Here is a solid. A really bad diagram for a solid, but I'm whizzing through. But if the light has to go through air, it might get slowed down slightly. It's very difficult to measure that, but it does slow down slightly from space. But obviously passing through that, it will get through that no problems. When it hits particles, you imagine it slows down. Like trying to run through water, it slows down. As soon as it exits, it goes back at the same speed. Now, light travels at 300 million meters/s. So, when it goes through glass or plastic, whatever it is, u it will slow down. So, let's say for argument sake inside the block it goes at 200 million meters/s. Still too fast for us to really measure uh these sort of distances but we can actually see the effect which it has and we can actually use some clever maps uh to actually work out the relationship between the angles and the wave speed but for this it's not something you have to do on the GCSE so again the angle going in is known as the angle of incidence when light goes in because it's going into a more dense medium it slows down and therefore it bends inwards towards the normal. So the light ray should have gone in this direction but in this case it's caused it to bend inwards. So therefore this is what we call the refracted angle. I'll label this R. We always measure from the normal. We always measure from the normal. Let's give this a value. Let's say this is 30 for argument sake. Let's say that's 20. So we can see the light went in uh it went in and it bent towards a normal. And when it leaves because it's returning back to air again, it'll go back to the same angle. I could put a normal on there and that will be 20 and this one here would be 30 because it represents the same angle going in. It's going out.

Now you might be asked um how to set up that experiment. This is one that's come up quite regular being a core practical. So very simply um put a glass block on a on table over a piece of paper. Shine a ray of light going in. Mark the rail light that's coming out. Join them up. Draw a normal line on. Measure the angle of incidence. Measure the angle of refraction etc etc. And it's it's quite straightforward to do but just stating draw around the block using a pencil. Um, use a straight line ruler. Draw on the ray of light going in. Draw the ray of light going up using a ruler. Join them together. And you can see just by stating the equipment, you're obviously putting yourself in a position where you can get more marks. Draw a a normal line at 90 degrees from the interface where the light meets the block. And it's just developing those answers just a little bit further so that when you're coming to answering marks, just trying to maximize as many marks as possible. So that's one way we can set up refraction. And it's just talking about how light goes into a more dense medium, it slows down and therefore it bends towards the normal.

Right? Now, um, how is this really relevant then to some of the other parts? Well, it says on here compare refra refraction of sound and light. Now, um, there's a key difference really between sound and light. And I'm going to use water as an example. Now, this is going to be a very flat day on the water. So, this is my water. On the top, I've got my air. And on the bottom I've got my water. Now water is obviously more dense in there. So as we would say with light and I'll come in at this angle here. This is my light ray and it goes into the water and because it slows down it will bend towards the normal. Now if I go in the same effect here with a soundwave and remember it would in fact I'll show you that in a second. If I do the same with a sound wave now sounds very different than the light in that it does refract. However sound requires particles to move the more particles and more dense the faster sound can move. And in a sense this is what's happening inside of a solid. So here are two solids. This has got a few particles in. This has got many more particles in. So, it's more dense. Let's say this is plastic versus metal. If I hit it um if I hit either material, they can conduct the sound through. And what's going to happen is the particles will vibrate getting kinetic energy and then it will collide into the one next to it. That will vibrate and that will collide into the next one. And then that will vibrate and the sound energy will transfer through the device or through the object. In this case, because the particles it's more dense more dense, the particles will collide into each other a lot quicker. There's not this space between there's not as as fast sorry as much of a delay. So what will happen as soon as you hit it uh let's say this one took two seconds for the sound to transfer through. It could be a really long distance uh for example and this one took only 1 second and that's simply because when you strike it the particles collide with the particles next to it and therefore transfer the kinetic energy much faster. Now the point I'm getting at with this is sound travels faster in more dense particles. And that's really when we're talking about how fast sound travels. I apologize about my pen. um in air in liquids like water for example I should have put gas really there that's be and obviously in solids there is a clear difference between the speed at which solids gases and liquids transfer sound so let's pick a random gas but gas in air is about 330 m/s and that's because there's only a few particles in in liquids for example now I'll do this as it's got a surface They're very dense. They're very close together. They are randomly arranged, but because they're close together, sound, let's say in water would go about 1,500 m/s. Depends on what minerals in the water. So, this could vary slightly, but uh you get the point. Salt water might travel a bit faster because there's more particles in between the water molecules and therefore particles sound can travel faster. And then solid, they're very tightly packed together. They're more dense. And if I pick that metal object, this one here, the one that was really dense, for example, don't uh show my diagram to Miss Taylor. She'd be very upset with my uh my solid liquid gases particle diagrams. Um, but um because they're a lot more dead, excuse me. Um, and you know that if you pick up a really heavy chunk of metal, it's really really heavy. That will transfer sound a lot quicker. So let's say 500 meters/s. Now, I'm making up that some of these, well, I'm making up that value. They're all sort of close to none of them are exact.

Now, the point we're getting at if we're going from an air to a liquid, um, the gas or the speed of sounding gas is speeding up when it goes into a liquid. So, where it slows down, it bends towards the normal. In sound, it'll have the opposite effect. It'll actually bend away from the normal. So, um, so when, and it doesn't matter if it's going in or if I change the arrows around, if it's going out, it will go really quickly and slow down. So, it bends towards the normal if it's going out or it's going sound going into water, it's going very slow and then it speeds up because it's going into a more dense medium. Liquids obviously, sorry, light obviously has the opposite effect where light slows down with particles. Now, if you're asked to do a comparison of these, one of them could be draw a diagram to represent it. Now, I've drawn arrows as it was going out or arrows as going in. Either way, it doesn't make any difference. Just be aware light slows down in more dense materials and more dense mediums. Sound um sound will speed up. So, we get this effect of bending towards the normal or bending away from the normal. Okay.

Right. Now um so going through a comparison of them just take your time on explaining what's going on why it's going on what's the different densities you can just discuss some of the wave speeds if you can remember some of them an example of these I could put 300 million meters/s and put the correct out zeros and I could put 330 m/s and obviously when it goes into water put 1500 meters/s and then um let's say 1,500 It's dropped by half, 150 million, should I say. Right. Okay. So, you can see obviously there's a difference in speeds depending on what it is that's carrying the energy mechanically, whether it's a light wave or the sound wave and what's going on with the wave speed and refraction as such.

Now, that takes us on to the next bit and now I'm going to talk about critical angle. Now, critical angle is basically an angle where refraction can no longer take place. and we get what's called total internal reflection. Now I will do a reminder of this. Uh, we tend to see a um a semic-ircular block. Um, as soon as you see a shape like this, assume we're going to go on to uh critical angle or total internal reflection. Um, so what I'll do is the um I'll I'll do a couple of drawings of this just to make it easier. But the first one, you can see we've got this circular um side of our glass block. And the reason why it's circular is so that I can shine a ray of light in here at any angle and it will meet the surface per at 90 degrees from the surface. Remember we talked before about uh it will reflect off but in this case it's going to go straight through going to transmit through into the block and because we're going in at 90 degrees from the surface even though it's a curved surface is going in a straight line. So the light is going through. Now just as a reminder of that if you shine light through a normal or sound through a normal I'll just draw my array of light going in because it's going through the normal whether it cannot bend towards a normal. So um light or sound going through the normal will just go in a straight line will not got the effect where it bends. What we will have is the effect where it uh that it slows down and you can do some different measurements to do that but it's not relevant for the GCSE.

Right going back to this then so light is going from u from air into a block it's a semic-ircular block semic-ircular so light can go straight for the normal in a straight line and that's so we can control how light is meet how light is meeting this interface on this side now we should know already light is going from a less dense sorry more dense to a less dense medium and in this case because it's light it will uh bend away from the normal. Now what happens is we can change this so it can go this way and if we go towards this way the light will bend towards this way. If I um move my ray box this is coming from my ray box and I move it at further angle. So I start to move it this way, the light ray will go at a different angle. Now I'll draw this in here. But in a sense, if I start to increase the ray box angle from the normal, what will start to happen is as I move the ray further away from the normal, this ray of light will start to move closer towards the interface. Now what will happen at some point as I start to increase this angle let's call it the angle of incident. So I've increased this angle the refractive ray will eventually get closer and closer towards uh the surface and eventually we'll get to what's known as the critical angle. Now the critical angle my drawing is just getting worse and worse is the point at which light will go through the block and is refracted completely across the surface. So this here is known as the critical angle and that's where we've increased the angle of incidence so much that the refractive angle will increase more and more and eventually the refractive angle will reach 90°. And at this point we can see it's been refracted across the surface. So it's refracted at 90 degrees. Now what that tells us is we can no longer increase this angle anymore because it cannot refract anymore in the air. What's going to happen? It's going to be passed straight back through this um this glass block again. Now what the effect we get is I'll try and do this a little bit neater. If we go past the critical angle um and this is when C or critical angle has gone past whatever it whatever the critical point is. This will be different for different surfaces depending on the density of the glass or depending on the density of the plastic or what whatever the material is that you're using. Uh the the amount of refraction will differ. Now at this point light is going through. We've gone past a critical angle. So what happens is something called total internal reflection and that is where we are past the critical angle light can no longer refract in the air and it's gone past the point where it refracts along the boundary and therefore all light instead of being refracted down here the surface acts like a mirror and therefore light is totally internally reflected. I don't know what I was writing there.

So, um, you can see you can see obviously if you increase your angle of incidence past the point which is the critical angle, the critical angle is the point where light is refracted along the boundary, you could say 90 degrees from the normal or across the boundary. If you go past that point, the surface or the interface then acts like a mirror and all the light is totally internally reflected at the new boundary. So, um, it's quite quite an interesting one for it to come up, but really if you just take your time on it and just go through a couple of the key points. So, in a sense here, we've got our incident ray and we've got our refra refracted ray. So, light is going from the glass out to the other side into the air and it's being refracted. Light speeding up and therefore it's bending away from the normal. If you increase the angle of incident, eventually you'll reach the point which is known as the critical angle. And this is where light is refracted along the boundary. And at that point, if you go past the critical angle, all light is totally internally reflected and the inside surface is a mirror. So repeated that a few times. It can be a little bit tricky to explain, but really just take your time to explain it if it comes up on the exam, which it should do because it's in your revision list. So I don't know what form they will ask you these sort of questions. It might be how could you set up an experiment to do this. Um, so you just take your semic-ircular block, shine a ray of light in uh and then measure the refractive angle coming out the other side and start to increase the angle of incidence until light is refracted along the boundary as such here and therefore you've reached a critical angle. Uh, again some uses of this is things like fiber optics and this is where we can shine light through materials going back wide angles and we can use that for things like the internet without using

Okay, this is going to be take two. I'm going to have to trim this. Um, so if you're looking about the dodgy uh fusion of videos, I made a bit of an error on the last one. So I'm going to be starting now going through sound. Um, now uh although I have touched a little bit on sound quite a lot on sort of waves on this topic I'm going to be particularly focusing on infrasound and ultrasound. As a quick reminder sound um travels at different speeds through different mediums more dense faster travels excuse me there is a little bit on human ears that we have to learn. Um, I'm not going to spend time going through it now because it's not necessarily irrelevant, but the human here is sensitive enough to pick up the following frequencies. It's anywhere between 20 and 20,000 hertz. Now, that does deteriorate over time. You would want to use ear defenders, for instance, if you are going to use loud sounds to protect your hearing. Uh, but naturally, it does degrade over time due to um obviously getting older. So, for example, uh you will all probably most of you be able to hear much higher pitches than me. Uh, I can hear 13,000 hertz. I'm sure some of you 15, 16, 13 plus. So, if you can hear outside the ranges of human hearing, so 20 to 20,000 hertz. If you can hear more than 20,000 hertz, for example, 30,000 hertz, you can hear what's called ultrasound. So, you are super human. Now, obviously, we don't hear that, but certain animals can. Bats, for example, can hear very high frequency waves. Um, we can also utilize them for things like sonar and ultrasounds which I'll touch upon in a moment and there's also u infrasound which is tends to be sort of the earthquake zone. So uh we're going to use earthquakes sort of to take measurements um where infrasound is really where most of the questions will come and that's used for sonar which I'll touch upon in a second and obviously ultrasound. Now these are relatively straightforward really in terms of if you know your science it should be quite straightforward. Do you know what refraction is? You know how to calculate the speed of a wave. However, they do ask you in slightly different contextes and some people can get a little bit stuck particularly when you start talking about uh milliseounds or remembering about distances etc. So the one I'm going to use I'll use sonars first. So this is my boat. None of you were invited. Put some uh put a uh nice little flag on. That's enough for Mr. Rimmer. Put my sunglasses on. There we are. Good times. Right now, whilst I'm sailing my boat, obviously I don't want to crash it. So, I want to know what the depth is of of water. Now, you might notice this actually if you go on a holiday. Um, when you start to go to shallow waters, they actually put flags everywhere. Uh, which sort of bobb up and down or big boys which bob up and down on top of the water and it tells you about the depths. Uh, but lots of fancy boats don't have that lux don't have the luxury of seeing flags everywhere if you're out at sea. So, um, they have to have something that's using sonar. Now, that could be using uh detecting fish as well, shors of fish under the ground. But let's say there is some uh quite uh large underground mountains. I don't particularly want to hear hit them. So I have to find out what the depth is. And we use sound to do that. And it's ultrasound and it's called sonar. Now all you do is you send out a signal that comes from a transmitter. Once you've transmitted the sound, uh then that's reflected back. And what we can do as long as we know what roughly the density of water is or how fast water transfers through. Now we know I've said this before, it's 1,500 m/s. Salt water might be a bit faster. If it asks you to do a calculation, as long as it's not calculating water speed, assume you'll be given it. Otherwise, assume it's 1,500. Um, so, but the speed of sound uh in water travels down and it travels back up. And let's say it takes uh two seconds to travel all the way down and all the way back up again. U now, you might have seen already, we can work out what the distance is. If you use speed equals distance over time, rearranging it, distance equals speed times time. If you need practice rearranging, always ask. Always happy to go through it. And what that tells us is the distance for the wave to go all the way down and all the way up to work out what the depth of the of the of the of the um round is. Um, you could simply just need to do that very simple calculation times your speed uh by the time. So in this case, 1,500 times by two. But that will tell you the total distance travel all the way down and all the way up. We just want to know the depth. So there we thought you need to divide it by two. Now you could divide the distance by two. You could divide the speed by two. You divide the time by two or just divide the whole lot by two which I prefer to. So speed times time uh divided by two. Just read the question because sometimes they might give it you in a completely different context and therefore you need to times by two. But in this case it's simply work out the depth, the speed and the time for it to go all the way down and all the way up. We only want half of it. we divide it by two. So, it's very simple in this case. 1,500 * 2 / 2 equals a depth of 1,500. So, relatively uh deep water. So, I should be all right. Obviously, if I start sailing my uh boat over here, uh then obviously there's more chance of a potential collision if that raised bit is uh high enough.

Right. Now the next bit you they can sort of determine or go on to um is ultrasounds. Now trying to just think of a good example of this. Here is a baby developing in a womb. Now um inside of a womb there are there is a liquid um and then obviously the skin. Now this is obviously not designed to be a particularly good picture um but in a sense an ultrasound works very similar where we can find the depths of things and if we know the depths of different surfaces we can start to make a image with that. So what we do is we get um an ultrasound um device which sends out an ultrasound, transmits an ultrasound out and it'll also have a receiver on and what that will do is it will send out basically a pulse and remember that will be a sound wave. So it's longitudinal. When the pulse is sent out it can uh reflect off the surface and not much gets through. So we need to use a gel. So that gel is used. It's quite cold. If you've ever had ultrasound at physio, um then you'll it's basically the same device. It basically puts a gel on and therefore they can take a scan uh without the waves bouncing off. So they'll reflect off the surfaces. This is about the same density as the skin and therefore all of the waves go through. Now you might get a question based on surfaces when it goes through and transfers from one medium to another. Remember this is skin, this is liquid. They might have a different density. So it might refract a little bit and when it goes back it bounces off and reflects back. It can obviously refract a little bit back as well. So some of the energy could be lost. Some of the waves could be lost because it could be absorbed by the skin. Some of it could be reflected of course when it hits a different surface. But most of it will travel straight through. Now um once it travels through it hits the baby and reflects back off the baby. And what this device will do, it will time how long it takes for the signal that sound that it's come out to bounce back. So it's simply timing how long that sound has taken to travel that distance. But it has lots and lots and lots and lots and lots of little detectors on and little signals that it sends out. So let's say here are the ears, here is a nose, here is some eyes. It's a very sad looking baby. Um um and what that is uh what the device is so good at is because it sends out loads of little signals at once and picks all the different signals up separately. It can actually determine all the different distances from the distance of the ears, distance of the eyes, distance of the mouth, etc., etc. So so much so it can you can determine um the sex of the baby for example. Um, so what it does it picks up all the different distances and it sends it to a computer and it's very clever. it'll start to convert all those different sound waves and the different distances and the different times to work out basically what the features of that baby is. Uh, I was going to draw it then but I'm not I'm not even going to try what the different features of that baby is. Now you might get questions related to this. Uh, what happens at the different surfaces? It can reflect, it can refract, it can be absorbed. Um, so some of the energy can be lost. That was a question that's sort of tied in uh to a previous exam. Um, you might get a question asked to work out um some speed distance time related. So just a reminder it's got to travel from here to here. Now in real terms it's not a large distance and sound travels really fast. 330 m/s we're only traveling maybe a couple of centimeters or 20 cm for example. So therefore the timing will be milliseconds. So let's say it gives us a time of 20 milliseconds. Um, sorry I put meters/s apologies. 20 mill seconds. And it might ask you to work out the distances. So distance again is speed times time. Might ask you to work out the speed, but just be aware milliseconds. You would need to divide by a thousand because there's a thousand millimeters into in a meter, which will give you 0.02 seconds, for example, times by whatever the speed is, and it'll tell you how to determine the distances accordingly. So just be aware of that. That's very similar to sonar. And the sound waves have to go all the way there and the all the way back. So the distances might be half the distance just depending on the type of question it might ask you to

S waves and P waves. Now, right now the key difference between both of these they are produced with seismic activity. So through earthquakes we've got an S-wave and a Pwave. Probably should have done these the other way around. If I I'll start with a Pwave first because Pwave is known as the primary wave. Now the primary wave is the one that is sent out first. Um, and is usually I say usually is always a longitudinal wave. And what does that mean? It means uh the particles vibrate forwards and backwards. Push and pull. You got rare fractions, compressions, and the energy is transferred forward. S-waves, they're known as the secondary waves. They are Now I'm going to say transverse wave and slightly different is transverse wave particles vibrate up and down and energy is transferred forwards. So the big difference between the two of these is um is just how the particles oscillate or vibrate. So uh in transverse wave particles vibrate up and down energy transfers forward or particles vibrate perpendicular at right angles from the direction of the wave. Longitudinal waves particles vibrate forwards and d forwards and backwards uh parallel to or in the same direction of the wave.

Now when we're going through these um they're usually used in terms of being able to describe what the different layers of the earth is. So, here is the air. I'm not going to go through this in any great depth. I'm basically just going to do two layers of the air. So, we've got the outside layer and let's say the inside layer. Now, this is going to be a solid. Now, the Earth's crust is a solid. Uh, the mantle is a mixture of liquids and solids. And obviously, the outer core is a liquid. So, this is the same Earth twice. Now, um, we'll start with the Pwave. Now what happens is at the epicenter, the epicenter is simply just where the earthquake takes place. Um, it starts to send out lots of waves through the earthquake and they can be picked up through large distances. Now let's just assume this area on the outside is a solid and I'll just put an L here for a liquid. Now we could say the S cross, we could say the S mantle is a solid. The outer core is a liquid. Let's just assume that for the moment. Okay. Now, mantle being a bit of a mixture of both. Now, when the waves are sent out, rather than going in a straight line, they'll start to arc a little bit. The reason why they arc is because they are refracting. That's because there are different densities um inside of the inside of the earth and it causes it to start to refract. Now, again, if you had some really dense rocks, some of them might reflect off those dense rocks at different layers. Um, but we're going to ignore it for this example. Now what happens is um longitudinal waves or P waves they push and pull but they can go through liquids. So I'm just going to refract this one just at the surface here. So all of these waves can be picked up at all of these points of the earth. Now if you sending waves into the liquid, they actually refract in and then back out again. It's actually the same here. They refract in and then they refract back out again. So um you end up with all the waves being sent through except for this zone here and this zone here. Now these are called a shadow zone. Now, by the fact you can pick up two shadow zones at different parts of the way, at different parts of the earth, basically two far corners away from the epicenter will

tell you that this is um a Pwave. So, it's the primary wave. It's the first wave that has been sent out from the earthquake now or the fastest wave that transfers out.

Now, a sec the aftershock sometimes they call it the secondary wave, the next wave that comes around. um or the second wave should I say that comes out or is transferred through is a S-wave and it's quite simple. Pwave a primary S wave for secondary being one. The Pwave travels first, the S wave travels second.

Now what happens in this case? Well, um the waves um will again refract as they did before. And obviously I'm doing these with arrows, but they are arcing as they're traveling through the air through different densities. Um but unlike a Pwave, S waves cannot travel through solids. So if they're refracted towards the solid or sorry they cannot travel through through no transfer through liquids. I apologize. So they can travel transfer through a liquid. Sorry, let me start that again. I'm obviously been going for too long. They can um refract or transfer through a solid or transmit through a solid. They can S waves cannot go through a liquid.

Now the reason why this is important and I'll just refract this one across the boundary and I'll refract this one across the boundary. Any other waves is absorbed by a liquid core. The reason why this is important is we can actually tell whether there is an S wave or a Pwave which has been sent out because about half the air will be in a shadow zone. And that's simply because S waves can't travel through the center or through liquids and therefore that will tell us that um half the earth will have a shadow zone. So it must have been an S wave.

Now what the applications used for and how are these different? Well the first thing we can do is we can actually determine what the different layers of the earth is made up of. For example, um we haven't really been below maybe two kilometers into the earth because it starts to get really really hot because obviously the rock starts to turn molten. So what we can do is we can actually use earthquakes to actually determine what the different layers inside of the earth. Are they a solid? Are they a liquid or are they a gas? Now obviously it's unlikely to be a gas.

Now one way we can tell what the different layers of the earth is is by using a PNS way. So we can actually determine that a chunk of the earth is made of solid and that's because sways will refract but absorbed by a core and that's why we have a large shadow zone. We can also determine that the center of it must be a liquid and that's because P waves will will transmit through the earth similar to an S-wave but they will transmit through a liquid. So they can be picked up at the other side of the earth. But we do have two shadow zones and these are where these Pways are refracted away from. So we can actually use S and P waves to actually determine what the different layers of the Earth is made out of.

So we can clearly say some of the Earth is made of solids. What tells us that S waves determines that some of the some of the Earth's core is made of solid? And that's because lots of it is unable to pass through to the other side of the air. We can also determine that it's most likely liquid is because if we use Pways, Pwaves will travel to the other side of the air, but we have these shadow zones as a result. So therefore, you can use both of these in different regions. You can actually explain um what happens with the waves. Are they refracted? Are they absorbed? And you can also say, well, what does that tell us about the layers of the earth?

Well, S waves instruct us that a chunk of the air is solid with liquid core because it gets absorbed. Alternatively, P waves um will travel through. But as we have two shadow zones, that will also indicate that liquids can go through the center. The center is a cut is a liquid core and we end up with shadow zones where it's refracted away. So, we can determine are there different layers of the air or solid, liquid, I was going to say gas, but obviously no, that's not the case, right?

I think that's pretty much it. So, I'm not going to spend any more time going through any of that. I hope this was useful. I apologize. It's listen to my voice in your own time. Probably about an hour. Um, so I'll not make this any longer. Well done if you made it to the end of the video. I won't say like and subscribe. Just dislike and don't watch ever again, but hopefully it was useful anyway. Um, and I apologize a little bit longer than I expected, but I'll try to go through it as much depth to give you the best opportunity to do well. Anyway, have a lovely day. See you soon. Think about