I get (or think I do) that different frequencies (or colors) of visible light refract differently i.e. move at different speeds through a piece of glass. But then why do they need to enter at an angle? Wouldn’t simply passing through any refractive substance do the trick? And please… like I’m 5….
In: Physics
Alright, let’s give a good example for this subreddit.
Imagine a racing car, 4 wheels on a track. At top speed the care goes at incredible speeds and can never be over taken. But now imagine the car in a couple of scenarios whenever it goes into the gravel on the side of the track.
1) the car doesn’t even steer at the corner of the track, it flies of at a 90 degree angle. In our minds we slow this down, we see both front wheels going of the track at the same time. Immediately the car slows down.
2) now imagine the same racing car, but now he starts to steer, but still manages to get into the gravel besides the track. When we slow things down in our mind experiment, we see that the front wheels do not hit the gravel at the same time: the car is coming in at an angle.
Due to one wheel still being in the track, and the other being in gravel, we expect the car to start turning. Why? In our example the wheel still on the track is wanting to keep going at the same speed, while the other is slowing down.
(This example always helps me remember which way the light will bend.)
To understand why light feels the need to refract is more complicated. As many pointed out in this comment section: it is due to the wave like nature of light, which needs to be explained further.
Imagine our race car again. Except the race car is no longer a single race car, but for our science experiment it is constructed as a long row of 5 racecars, all attached to each others sides. Their wheels are connected, the front of each car exactly lines up
Like this:
(Traveling in this direction)
^
|
O-O-O-O-O
Now imagine that row of cars actually driving, and having to take that same turn. You can imagine that a part of the 5 car row would not even fit through the corner! It would already be in the gravel before the center car starts steering.
This is how you can imagine the wave of light! The light wave itself is the row of cars, their wheels connected. As a part of the row enters the gravel, it has to slow down, it cannot keep up the high speeds. It starts to slow down the row starts to turn, but the other cars are being swung around, in order to still hold op their line formation!
Oh god I almost forgot the prism part.
The prism is the difference in tires of the car. One handles gravel better than the other, slowing down at different accelerations, the car seems to turn differently when it hits the gravel.
If they hit straight on (at 90 degrees) they might slow down differently but you can’t see any difference in the beam because they all follow the same track. The red light may be a few wave crests behind the blue but you still have a mix of red and blue together. When they hit at an angle, the different rates of slowing mean they bend through different angles and so follow different paths and you get separate beams of red and blue (and the other colours)
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