Total external reflection
Do you know how sometimes when you're trying to look at something inside a room from outside, you can see it clearly through the window? But other times, you can't see anything at all, even if the lights are on inside? That's because of something called reflection!
Reflection happens when light bounces off of a surface, like a mirror or window. Sometimes, when light travels from one place to another, like from air to glass, it can reflect completely back into the first place instead of continuing through the second place. We call this "total external reflection."
This happens because of something called a "critical angle." Think of it like this - imagine you're trying to hit a ball over a net. If you hit it at just the right angle, it will go over the net perfectly. But if you hit it at a different angle, it might hit the net and bounce back. The same thing happens with light - if it hits the surface at just the right angle, it will reflect completely back instead of passing through.
This is why sometimes you can see through a window and sometimes you can't - if you're standing at the right angle, the light will reflect completely back to you and you won't be able to see through the window at all! It's pretty cool, huh?
Reflection happens when light bounces off of a surface, like a mirror or window. Sometimes, when light travels from one place to another, like from air to glass, it can reflect completely back into the first place instead of continuing through the second place. We call this "total external reflection."
This happens because of something called a "critical angle." Think of it like this - imagine you're trying to hit a ball over a net. If you hit it at just the right angle, it will go over the net perfectly. But if you hit it at a different angle, it might hit the net and bounce back. The same thing happens with light - if it hits the surface at just the right angle, it will reflect completely back instead of passing through.
This is why sometimes you can see through a window and sometimes you can't - if you're standing at the right angle, the light will reflect completely back to you and you won't be able to see through the window at all! It's pretty cool, huh?