By magicians. And it's actually got a name, peppers ghost, because it has been used to make it seem like there is a ghost. And I'm just going to show you a little video clip and then a diagram so you can understand how it works. And then I'll mark this for you after the lesson. So let's get the video clip up first. Right? It's not that one. So let me load it now. It's not necessarily the best video, but it. Helps you to understand what's going on. Can you see the candle burning in the glass full of water? So this illusion, as I said, can sometimes be used to make it seem like there's a ghost there. It can also make it seem like there is a candle which is actually on lit on the side where the people are, but it appears to be lit, but they can touch it and they can feel that it's cold. Or this one where there's a candle underwater. So let's see the setup for this and work out how it works. Okay, so back to the rigitic. I might forward some of the bits, candle burning, the glass full of water. Let us see what is behind this magic. You need a plain sheet of glass, candle, matchbox, water glass and four wooden blocks. Hold the glass sheet work little by supporting it with wooden blocks. Okay, so it's not a mirror, it's just a sheet of glass. Keep a burning candle in front of the glass sheet. Now keep a glass on the other side of the glass sheet at the same distance as the candle is from the glass sheet, so the distances need to be the same. The glass sheet should be perpendicular to the line. Join the glass and the candle. Now fill the glass with water and see the setup from the front side. You will see that the candle seems to be in water. Let us explain this magic. The glass pane reflects some of the light incident on it. So we get an image of both the candle and water on the same plane of glass. Okay, so let's read that. So the glass reflects some of the light. So because the glasses are quite a shiny surface, we know that transparent surfaces let light PaaS through them, but they reflect some of that light as well. And that's why this illusion works, because of the reflection. So we get an image of both the candle and the water on the same pane of glass. These two images overlap, giving the illusion that the candle is in water. It is important that the candles are properly aligned for the illusion to work. The illusion can be viewed from almost any angle. And of course, you can also picture that you could do the same thing with two candles, one of them being lit and the other being unlit. And if you line those up perfectly, so you get the flame above the wick of the unlit candle, then it looks like you've got a magic candle that has lit itself, even though it's completely cold. So just go to show you a diagram of that as well, just to help explain that a little bit more. So this is the diagram with the lit and unlit candle. So glass is mostly transparent. There is still quite a high proportion of light reflected that hits it. So normally the light going straight through is much brighter. But if you use something bright like a candle in front and a dim room behind, then the reflection can dominate what you are seeing. So you have the bright thing in front on your side and then it's dimmer behind. So okay, linger. Are you happy with that? Understanding how that works? Yeah, Yeah, brilliant. So where are you up to in your science lessons? What have you covered? I think we are having like a test or something soon, but we were doing the eye. Okay. It sounds like you've nearly finished then. Have you done color? No, we're doing it. Next lesson. Brilliant. So you've done reflfraction. You've done refraction as well. Yeah, I think the eye and color and then you'll be finished. Okay, that's good then. So we're on refraction today and a little bit about prisms as well. So can you read this learning objective? To explain the process of refraction when light travels through a new medium. To identify the angle incident, refraction and emergence in the ray diagram. To explain reflection action as a result of light changing speed in different materials. To explain how reflection causes a dispersion of light. Very brilliant, right? So I presume we don't need to do this. I presume that you are confident measuring angles. Yeah. Do you feel confident with that? Linda, Yeah, Yeah. Okay, we can skip past that then. So what do we notice about the image of the pencil when it is in water? It doesn't become like a straight line. Good. So it looks like Yeah like it has bent. So it looks bent or it looks like the pencil has been snapped. So obviously it has not been physically altered. So something is causing it to look bent or broken. And this is due to refraction. So the light reflecting off the pencil is being bent because of the water. Exactly. The ableg happens. If you've ever been in a swimming pool and notice that the bottom of the pool looks much closer to you than it really is. So which is easier, walking through air on a pavement or walking through water, walking to air? Okay, of course. So water is denser than air, and it is harder to move through. And the same thing happens to the rays of light. If a material is transparent, light can PaaS through it, but light will travel slower through denser materials like water. So the light has been slowed down due to how tightly packed the particles are in water compared to the particles in air. So we know that the speed of light in a vacuum is 300 million m per second. In air, it is slightly slower now, not by very noticeable amount, but just the fact that it is slower means that it is bending. So it's slower in air and then a little bit slower in water. You can read this slide, please, Linda. Imagine you are driving a car on a road which goes from being made of concrete to being made of mud. Since it is harder to drive doing mud, the car will slow down when it reaches a boundary between the road and the mud. If you drive forward at a right angle to the boundary between the road and the mud, then the color will continue in the straight line while slowing down. However, if you dry any other angle, then one of the front two wheels will slow down sooner, then the other will cause a car to turn. Now this is just a model for you to try to understand what is happening to those rays of light. So if you are hitting it straight on, it's just going to slow. So we're not having any bending. But if you are here to get at an angle like this picture here, we're going to have a bending happen. So we could see this now with our ray diagrams. So air to glass, air is obviously less dense. But if the ray of light is hitting it exactly perpendicular, sorry, at a right angle, then it's going to go straight through. However, if we are hitting any other angle, then we have got a bending. So of course, this is what it would look like if it was continuing at the same angle. But we have got a bending towards the normal, do you agree? Yeah. Yeah. So when we go from a less dense to a more dense material, we have got the ray bending towards the normal. It is slowing down. Remember, this normal is an imaginary line which is at 90 degrees to whatever boundary it hits. Get rid of my line. When light enters a dense medium, it slows down and bends towards the normal. What about if it's the other way round, from a more dense to a less dense? Bds away from the normal, okay? So when light enses a less dense medium, it bends away from the normal good. So we can see all of these with a block of material denser than air. And this one will be glass, or perhaps it will be perspecs. So starting down here, number one, number two, oops. And number three, would you like to explain what's happening, Linda? For the second one. It's bending. On. Is it bending towards the normal? Well, if we Carry the line on. Yeah, it certainly is. So do you want to start by telling me whether the ray is entering a less dense to a more dense material? At the beginning. At the beginning, it's entering up cancer material. Yep, so the ray bends ds towards so normal. Okay, how come. Because it's slowing down just a little bit. Yeah and then and then it's and then it bands away from the normal when and to a less dense place because the speed increased a bit. Yeah. Okay, brilliant. And what is the term for this bending? What's the proper term? Refraction refraction good. So now let's have a little look at some of these terminologies. So just like with reflection, our first ray is called the incident ray. And from our normal line, our dotted line, the angle between the normal and the incident ray is the angle of incidents. And then inside we have got the angle of refraction. It's time. And again, we Carry on our normal. Now which angle would we need to measure here inside what you notice about those two? The same. They're the same. So it doesn't matter which one you measure. And then finally, we have got our angle of emergence. So this is the emergent ray. So the word emerge. If you think about what that means, what does emerge mean? If we are talking about if we used it to describe a baby chick hatching from an egg. To come out. Yeah come out. Yeah. So you can remember, but that's the ray that comes out the other side of the block, the emergent ray. So what do you notice about the angle of incidents and the angle of emergence? The same. They're the same. Okay, I'm going to show you the quick video clip of this practical. Now I expect did you do this practical? Yeah, okay. Okay. So do you short clip and it's a good refresher to your memory. Let me get it. For this experiment, you will need a power pack, the ray box ruler, burn. You will need a power pack, a ray box ruler, attractractor pencil, glass or perspecs block. You probably need a rubber, and you need a blank bit of paper. Okay, people, drawing ray diagrams to show the refraction of light through a glass or perspecs block. Step one, we are going to put the, which is perspecs. You heard that word before, Linda perspecs. Any ideas? Is this like that glass sink? It's plastic. So it's just thick plastic. So sometimes in schools or when I was in school, when we went to secondary school, year seven, we had design technology. Do you have a similar subject? Technology Yeah where you go to have that, please, you have that in junior school. So where you get to use hammers and sows and other pieces of machinery like that, that's Yeah that I think that's dt for us. Dt, Yeah. Design technology. Dt, that's it. So the first project that you do in year seven, which everybody loved, they found it very exciting, is you made your own key ring. And basically it was, does any shape that you fancied, and you cut it out of colored perspecs, so just big sheets of thick plastic. And it was very exciting because you got to use a saw and then you got to use a special polishing machine and a drill. And that's what perspecects is. What things have you made in dt? We may be cut out shapes but not using plastics. And then we usually click down the f words and like a bunch of other words. Now we're like trying to make like a lamp. I made a little table out of mdf wood, and it was a little table for a vhs tape layer. Now they were like about this big. And you see the tapes? They were about that big. So they were a big rectangle because we didn't have blue rays dvd's. So I made my table for the telly to sit on and my dmy vhs recorder to sit on. And I got all of my measurements completely wrong and it was too small. So it was a bit upsetting. Nothing fit. Oh well. Okay. So that's what perspecx is, a glass or perspecs block down flat on our page. And we are going to draw around it. Step two, mark a point approximately halfway along the longer side of the glass block, and then you're going to use a protractor to mark a point that is 90 degrees from so he's just marking in his normal line here there from the edge of the block, and we're going to draw in a line. It's called the normal line. Now normally a normal line should be drawn as a dashed line. He's just drawn it as a solid line note. I have drawn the normal line on the outside of the glass block and about halfway through the glass box, you do not need to draw it all the way through. And we can label that normal mind. Step three, glass block is now back on the page. We have switched on the power pack and so our ray box is on shining a Rav light through the glass block. So what you're gonna to have in your diagram is our lines that show where the rv light went. And it's very difficult to fit a ruler in here and draw the lines now. So we won't do that. We will plot points that we can see. It's bending here, can't we? We can see that it's not going through. You can join up later. So you shine the ray of light so that it hits the glass block exactly where the normal line has been drawn. So you're shining the ray of light at the point where the normal line hits the glass block. We then plot a point showing where the ray of light come from. And now the tricky bit, you might be able to just faintly see that it looks like the ray of light is moving along here. But of course it can't be, because if you look, it's clearly emerging at this point. So what we do is we mark again, we plot where the ray of light is going, and we very carefully mark a point, the point where the ray of light comes out of the glass block. Like so okay, final step. All we need to do he's join up the points. So the ray of light came from this point here we put an arrow on, show the direction the light was traveling in. The ravellight emerged from here and went through this point. So we can draw that ray of light on. And again, we can put an arrow showing in the direction of the raay of light. And that means that within the block, the raay of light must have traveled along that path. Now you can see the light is not traveled in a straight line because it's been refracted by the glass block. What we then do is we can measure our angle of incidence. That's angle I and our angle of refraction, angle R. Now, did you measure the angle of emergence when you did this in class? So, no. Okay. The other thing you could do is mark, I won't show you how to do this, but you mark a second normal line at this point, and you can mark, you can measure your angle of instance, an angle fon this side as well. Okay, let's go on to this. So I'm going to give you some results now. Right. So can you transfer those results across to this worksheet, please, Linda? Like do I just copy it down? Yeah, copy those across just to get a set of results to work with. And if we just put a little degree symbol there, then that means you don't have to worry. About adding that each time. Yeah, and have a look at those. So what is the relationship between the angle of incidents and the angle of refraction? Is there actually a relationship? We can just say the general trend. So just the fact that it is larger. Now obviously only in this experiment because you're going from a less dense to a more dense. Now the angle of the incidence is larger. And the relationship between the angle of incidents and the angle of emergence. Now this is the one that you didn't measure. They are the same or depending on human error, obviously, you've got inaccuracies. When people are using protractors to measure angles, you might have got a little bit of variation. So they are the same. Good. Right, you've got some keywords here to explain refraction. So you want to talk about speed, you want to talk about light traveling from one medium to another and what happens? You want to talk about whether it bends towards or away from the normal. Okay. How am I T heard that again? How am I going use transparent? Don't worry if it doesn't work. So if it's transparent, it doesn't. So you could use it here. Refraction occurs because light changing speed as it travels to different transparent mediums. So Yeah, it could go there. Because of course, this isn't going to happen if the light can't PaaS through the material in the first place. And rather than two, should we have travels through different transparent mediums? Yep, good. And then you can do the less dense the ray bends towards. Away, sorry, wrong way around. So less dense it bends away from more dense it bends towards. Good. Away from the normal, not medium. Yeah p and then change the other one, change the other medium to normal. Right, refraction occurs. Let me read this now. Fraction occurs because like change speed as it travels through different transparent mediums, this changing in speed is a change in direction depending on the density of the medium. When the medium is less dense, it bends away from the normal when it is more dense. And you know what? Oh, we've said refraction. I was gonna to say, need to mention that word. Just put a full stop at the end. Okay, brilliant. Add that full stop in Linda. I don't need you to type that last question. We'll just talk about that one. Okay. So without typing anything, just tell me, how could you modify the investigation to find out whether refraction behaves differently for different materials? What other materials could you use? So this one used the glass. Block. What other materials could you use because they've got to be transparent. So there's not that many transparent materials, is there? What could you do it with the perspecs block? So that again Yeah so the plastic. And then what? Tracing paper? Yeah. Could try it with tracing paper. What about an ice cube? Youhave to work very, very quickly. But you could you could try it with a nice cube. And I can't really think of anything else which is transparent, but that gives you three different materials. And then you could see whether you got the same trend in results, okay. Great prisms. Let's look at this one. So a curious thing happens when light is refracted by a prism instead of a single beam of light. The emergent ray is a spectrum. So we have got our White light entering. And then we have got refraction. We can obviously see that we have got ending here. So that is. Not traveling in the same path. We've got refraction and then we have got the spectrum. So what are these colors, Linda? Can you name them? Orange, yellow. Green. Blue, indigo and Violet. Yeah do you have a little phrase to help you remember? No, you just remember it, okay? So lots of people use the phrase Richard of York gave battle in vain. I'm sure there's other ones, but that's one of the most popular ones. So Richard of York gave battle in vain, and that helps you to remember the order. So read this one, please. White light is made up of seven colors of the rainbow, red, orange, yellow, Green, blue, indigo, Violet. Light is a type of wave, and each of the colors of light has a different frequency. Different frequency of light would travel a different speed within the material. This means that they get refracred by different amounts. The red light slows down the least, so it is refracted the least, so that one is bending the least. Violet light slows down the most, so it is refracted the most. And you'll do a little bit more on this when you go on colors. So Newton was the first scientist to propose the theory that White light is made up of multiple colors. He used prisms to prove that each individual colcouldn't be dispersed any further. Fun fact, it is argued by some that indigo isn't a separate colso. There's not seven distinct colours in the spectrum. Newton actually observed five colours. He added orange and indigo to make it up to seven because at the time, that number denoted completeness. It can sometimes be hard to see those separate colors. Let's have a little look at some rainbows. Let's see if we can see them. Right. Can we see all of the distinct colors here? So I think the orange and the yellow the orange and the red definitely blend together. We can see the yellow and the Green quite distinctly. What do you think about the indigo and violets? Can you see those? Quite like. Like a bit Yeah they're blending. They aren't they? Let's see if we've got a different picture, see if it's any Yeah this one's even harder. How about this one? Yeah I'd say you can see them even less distinctly. So definitely you you can't make out the red and the orange. That just looks like red. So you can see the red, the yellow, the Green and the blue and that's about it. Can't really see any other colors on that one. So yet you can understand why people would dispute that. I'll do rainbows for make chance to tell me. How do we get a rainbow? Fraction, Yeah. Sunlight. Yeah, we need sun. What else do we need to see? A rainbow? Water, did you say? Yeah, Yeah. So sun and rain. So what is the sunlight? Enlike the water and slows down, making a bend, and it travels slower. And then the raindrops are acting like little prisms, aren't they? So they are diffusing the light. So they are separating the White light into all of the colors. When did you last see a rainbow? Like last week? And is there any sort of superstitions or anything surrounding rainbows in China? No, but it's not meant to be lucky to see one or anything like that. No, in the uk, some people think that if you can find the end of a rainbow, there will be a pot of gold waiting there for you. But of course it's impossible, because you can never find the end of the rainbow. So light gets refracted when it enters raindroplets. It is then reflected inside the droplets. So this is like the fiber optics. Do you remember? But we've got internal refraction. It is refracted again when it leaves, and this results in the dispersion of the colors, just like in the prism. So because we've got these changes in medium, so we've got less dense to more dense. So we have reection inside. But unlike with the fiber optic cables where the ray of light was staying inside, this time it's leaving. So then you've got the refraction, and that's when you get the dispersion. The reason you don't see a rainbow every time it rains is because the sun needs to be at a certain angle for rainbows to occur. And it's meant to be extra lucky here. Can you see a double rainbow? All we don't need to do that one. So what we're going to go on to now, right? So what would you like me to do next week? Because we've actually got let me just see how many more lessons so you're saying you think you've got one more lesson before your test. Is that right, Linda? Yeah. But like this test is like a review test. Like you can check the answers after you answer. Okay? So it's not an important test. Yeah. So when's the next important test? Like a long time after, okay? So we don't need to worry too much then. So we'll just continue at our pace then we don't need to rush ahead to do some revision. So let me tell you what we've got. Hang on, it's not on there. Close that. And just to check that, this is the same things that you are covering. So we've got colors and then we've got lenses, which is the I. So we've got two more lessons. Which seems pretty much Yeah seems the same as what we're covering at school. All we don't need to do the prism one you've done. You've seen the prism at school, have you? Yeah, okay, that's good. Don't need to do that. So have a quick look through the revision guide. And then we'll do this activity. Oh, I froze there for a minute. Right. Let's get on to the right section. Waves light waves 138. So for your homework, I'm going to give you some questions from this Cluso. We covered this. We had a little look at this superposition. Yeah adding together or cancelling out. So Yep, we did this one light waves. Speed of light calculations, reflection good, so specular and diffuse scattering now you said you haven't mentioned these terms at school. No, okay. So I'll give you this sheet, this page so that you've got it. Okay, this is all fine reflection, refraction. So that's just check that we have covered all of this so we won't read through it all. Let's just. Skim through it quickly. Right? Learn these really well. So this is about bending towards or away from the normal. That's fine. You know that. This is the model. So you could get a question and you could get a picture like this with a car, and you could be asked to explain how this relates to refraction. So that's the possibility. Right. That's fine. We've covered all of that. So we've got the eye and we've got color. So I'm going to give you some practice questions from there today for your homework. Let's go on to this. All right, Linda, let's have a look at this. So we've got three materials. We've got the thickness, we've got the time taken and we've got the speed of light. Now the thickness is obviously relating to the distance. So what's your first step? Distance divided by tide. Good. Making sure that your units. Are correct. Now it's asking here three significant figures. Yeah, that's it. Thank you. Hey, brilliant. Right? Order of density lowest to highest. So I'll let you scroll up if you need to. So looking at your results using the speed result, which one is the least dense? How are we going to tell that from these results? The fastest one is that's that the lower certainty. So our order is water, glass and diamond. Do you want to write up that in those three spaces? And then just a short sentence explaining how you determined that order. So the higher the density. Yethe slower the speed good. So when you shine a ray of light through a transparent block at 90 degrees, what are you going to observe inside your block and outside your emergent ryou? Don't to draw those in. So what's that ray diagram going to look like? Draw that in lender. Yeah, that's fine. You just do it quickly. So it's just going to be straight, isn't it basically? And then of course, always remember pop your arrows on because there's usually a mark given for adding arrows, right? What about this one? I'm going to draw the normal in just for red for you. I know it should be dashed, but I can't draw a dashed line on here. So there's your normal. So think about, is it bending towards or away from the normal, less dense to more dense? Okay, good. And then let's draw your next normal here. And then that's going to be bending away from the normal. And of course, these, oops, these and Oh, stop it, it won't change my pen. These angles should be equal, shouldn't they? And then this one, and this one, they should be smaller, right? Brilliant. Okay, Linda. So like I said, I'm going to give you a practice exam question for your homework and I will mark your homework sheet. Do you want me to give you that amount? Or was it too much homework? I think it's okay. Okay, I'll stick with that amount, and I'll see you next session. Bye. Bye.