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Course: Middle school physics - NGSS > Unit 4
Lesson 3: Transmission and refractionRefraction in a glass of water
Light refracts, or bends, when it travels across a boundary from one material into another, like from water to glass. This refraction makes a pencil in water appear broken. Understanding this concept helps us grasp how light behaves differently in various materials. Created by Sal Khan.
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- What is going on when the street seems to shimmer on a really sunny, hot day?(10 votes)
- Just like light bends when it passes from water to air or vice versa, it also bends when it moves from hotter air to colder air. When the road heats up the air above it, we see that the light doesn’t just travel in straight lines when we see these shimmers or mirages.
Does that help?(15 votes)
- Why does light bend?(9 votes)
- When light hits a glass, the object appears to bend due to refraction. Light does not always travel in a straight line, it just takes the path with the least amount of time. This is why the pencil in the glass looks bent.(9 votes)
- what happens when there is no light can refraction still happen?(6 votes)
- I would say no but I'm not entirely sure.(2 votes)
- So light bends?! WOW! Never new that till today!🙂(5 votes)
- what is "energy points"?(2 votes)
- You earn energy points from reading articles, watching videos (you get more for completing them), and completing/passing quizzes. The more energy points you earn, the more you can do with your avatar like if you have 1,000 energy points, you can get a certain avatar for your profile picture. You would need more energy to get an "evolved" version of that avatar or creature.
Mastery points are different. You earn them from your completion and accuracy of quizzes, unit tests, and course reviews. If you get all the mastery points possible for the course (like 850/850), you have mastered the course concepts.(4 votes)
- 2:02what does he mean by saying "Which typically would not see. That would have typically gone straight in that direction (shows direction) and not hit your eye."? Why would it have gone to the right of all places?(3 votes)
- Because the left side of the glass reflected the light to the right.(2 votes)
- I want to ask some questions about this statement "You would expect the point that would have been here would then go straight to your eye just like everything up here. But it turns out that that light, once it transitions from going from the water to the glass and then the air" is the light is transmitted from the air to the water to the glass?
first, where is this point exactly? on the surface of water?(3 votes) - If there wasn't any light would that still happen to the pencil?(2 votes)
- No. It wouldn't happen because your eyes wouldn't see it.(3 votes)
- Why does light bend in water(2 votes)
- What would happen if there are two fish bowls the left has a lot of fish but the right has one fish jumping into the bowl and on the top there's text that says "I ain't nothing like y'all" how would refraction work then?(2 votes)
Video transcript
- [Instructor] So
something very interesting is clearly going on when
we look at this pencil dipped in this cup of water. We would expect if maybe there
was no water in this glass that we would just see the
pencil continue straight down in a line that looks something like that. But that's clearly not what we are seeing. It looks like, once we fill it with water, at least to our eye, it looks like the pencil
gets bent or broken or bent in some way. And this notion, you might have heard
people call it refraction. But it's interesting
thing about exactly why this is happening. And I'll give you a hint. This is all about the bending of light. And it's not just light that can get bent as it goes from one medium into another. It can be any kind of wave. So let's think about
what's going on over here. So first, let's think about
the part of the pencil that is above the water. So this part right over here, the light is actually
reflecting off of this pencil, and then it's bouncing
straight into our eye. So just imagine a path from this dot straight into your eye. Once again, from here, it's
going straight into your eye. When we go over here, it still
doesn't look too distorted. So you have light that's
going straight to your eye. It's going through the side of the glass and then getting to your eye. But then once we get under the water, something's interesting. You would expect the point
that would have been here would then go straight to your eye just like everything up here. But it turns out that that light, once it transitions from going
from the water to the glass and then the air, it bends. So at the interface between the media, between those different materials that the light is traveling through, instead of going towards your eye, it gets bent, in this case to our left. And so that's why when
we look straight on here, we don't see anything in
this region right over here. But the light that was going from the pencil towards
this part of the glass, which typically you would not see, that would have typically
just gone straight in that direction and not hit your eye, well, now that is getting refracted. It's getting bent to the left so that now that light hits your eye. So that's why you see what
looks like a broken pencil. It's all about the light getting bent as it exits the water
and goes into the glass and then the air.