 All right, so why do we see the coin when I pour water into this bowl? Let's let's draw this setup and then try to understand what's happening. So here we see here is the empty container. This is our eye and this is this over here is the coin. So we begin when the container is empty, right? But we are not able to see the coin when the when the when the bowl is empty when the container is empty. So what's happening over there? All the light rays that are reflected off this coin, none of them are really reaching our eye. This light ray might have reached our eye, but it is blocked by one of the sides of the container. So when the container is empty, we cannot see the coin. But when we pour water into this container, the light ray that is reflected off of this coin, it travels in the water, then it comes across a change in medium from water. It has to travel in air and light travels at different speed and different mediums. As a result of which, when light travels from one medium into another medium, it changes its direction. And therefore, therefore we are able to see that there is a coin at the bottom of the bowl because a light that is traveling in water, when it reaches this boundary of air and water, it changes its direction and then it reaches our eye. This bending of light when light travels from one medium to another medium is called refraction. So we can see that light undergoes refraction and therefore we are able to see the coin at the bottom of the bowl. Okay, but we also saw that the coin appeared to be elevated. It appeared to have been elevated from the bottom and that's why we were able to see the coin. In fact, the bowl seemed less deep compared to original. The bowl seemed shallow and you can also relate to this, right? Whenever you see a bucket full of water, you can always see... Even not always, well, sometimes you can see the bottom of the bucket. So the bucket does not seem that deep. It appears as if the bottom has been elevated somehow. Why do we perceive things like that? So we can understand that if we extend this ray that is coming into our eye and if we do that, the extended ray can look like this. So what happens as a result is this coin appears to have elevated and it appears that the coin is at this position. In fact, the entire base seems to have elevated. So we see that the depth of the container or the bucket also seems less compared to when there was no water in the container. So long story short, the phenomena of bending of light when light travels from one medium to another is called refraction. And we can see many examples of refraction around us. If you place a pen or a pencil in a glass of water, you can see the pencil broken in the middle, right? Well, it's not really broken. What's happening there is also refraction. And have a look at this awesome image of a polar bear. Look at how much refraction is happening over here. It seems as if the polar bear is broken in the middle. But we know that can't be possible. So what's really happening over here is refraction as well.