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Current time:0:00Total duration:4:24

Video transcript

before doing more examples with Snell's law which essentially amount to some math problems what I want to do is get an intuitive understanding for why this straw looks bent in this picture right over here to do that let me just draw a simplified version of that of that picture so let's draw this is the cup right over here we'll do a side profile of the cup so this is a side profile of this glass right over here it's the best that I can draw it and then let me draw the actual straw so I'm going to first draw the straw where it actually is so it's coming in off the side of the cup and the straw is actually not bending and goes to the bottom of the cup just like that and then it goes up like that and then it goes slightly above it and then it actually does Bend up here up here right over here and then the straw actually does Bend that is irrelevant to what we want to talk about what I want to do in this video is talk about why when we look over here when we look over here why does it look like the straw got bent and it all comes out of the refraction of the light as the light from the straw down here changes as it goes from one medium to another now we know from refraction indices or in just in general that light moves slower in water than a dozen air so it's slower slower in water and faster in air and faster in air so let's think about what's going to happen let's think about what's going to happen let me draw two points of let me draw two rays that are coming from this point on the straw right over here so if I draw one ray one ray right over here so I'm just going to pick an arbitrary direction so if I pick one ray just like that now when it goes from the slower medium to the faster medium what's going to happen to it and set a slight angle here so the left side of the ray is going to end up in the air before the right side and I'm just using this as a way of you know the I'm using the car example to kind of think about which way this light's going to bend so if you visualize it as a car or sometimes people visualize it as a marching band the left side of the marching band is going to get out before the right side is going to start moving faster so this is going to turn to the right so it's going to turn to the right now let me do another ray so let me down on the rate is coming from that same point let me I want it to go right along the straw so another ray just like that it will also turn to the right so it is also going to turn to the right now if someone's eye if someone's eye is right over here so that's your eye that's the eyelashes that someone's eye you can even draw their nose and all the rest if they're looking down where does it look like these two light rays let's say there I is big enough that it captured both of these Ray's where does it look like these two rays are coming from so if you trace both of these Ray's back if you just say assume that there was a line here that's what our eyes and our brains do if you assume that whatever direction this Ray is currently going it is the Ray that it's the direction it came from and same thing for this magenta ray and this magenta ray just like that it would look to this observer that this point on the straw is actually right over there and it would look and if you kept doing that for a bunch of points on the straw it would look like this point on the straw is actually right over here it would look like we could do it for this point on the straw it would look like that point on the straw is actually right over here so to this observer the straw would look like this it would look like it would look like something it would look it would look like it would look something like that it would look bent this part would look even though the light from here is going up and then up and then it moves out because it gets bent when you converge it back it would converge to this just like we saw with that first point the light from this point when it goes out and gets bent if you were to just extrapolate backwards from there new directions you get to that point so to this observer this point on the straw will look to be right over here even though the light was emitted down here and that's why the straw actually looks bent why it actually looks bent so this is all really just because of refraction from going from a slow or medium to a faster one so hopefully you find that a little bit interesting the next video will actually do some examples with Snell's law just to get ourselves comfortable with the mathematics