Refraction And you

Parallel situation Imagine a cliff diver leaping off a tall cliff As they move through the air they move fast As they hit the water their speed slows down because the density of the water is greater than the density of the air

Light Think as light as a cliff diver. As it moves through a vacuum it moves fast (3.0x108m/s) As it moves though air, it is about the same speed As it moves through more dense materials it slows down (just like the cliff diver)

What happens to the light as it slows down??? As you recall speed is distance/time Therefore, if light slows down, it travel a smaller distance per unit of time This results in the light changing direction so that it can travel a shorter path

Shorter distance in glass = bend toward normal air glass 1 sec. 1 sec

To clarify: When moving from a low to high density material light will slow down and bend toward the normal (less distance per unit of time) When moving from a high to low density, the light will move faster = longer distance per unit of time = bend away from the normal

Index of refraction (n) = the ratio of the speed of light in a vacuum to the speed of light in the material it is passing through

Examples please The index of refraction for air = n air = 3x108 / 3x108 = 1 Wow that is really easy!!!!!!!!

Other materials n water = 1.33 Therefore the speed of light as it travels through water would be found by: Rearranging the equation:

And the answer is:

More materials please n ethanol= ? If C ethanol = 2.21x108m/s Here we simply use our equation: n ethanol = C vac/ C ethanol =

` 1.36 !!!!!!!!!!!!!!!!!!!!!

But why does the light bend? Rather than just slow down when it reaches the interface of different media. Think of a car that is moving down the road at a fast speed. If one of the front wheels slows down, the car will turn in the direction of that wheel

Some valuable values n air = 1.0003 n water = 1.33 n diamond = 2.42 n glass = 1.5 n plastic = 1.46

Snell’s law n = sin θi / sin θr Therefore: ni sin θi = nr sin θr

One last thing When light strikes the more dense material the frequency of the waves stays the same – but it is moving slower – so the wavelength must change.

Think about it like this: You have a stream of people going into a building at a constant speed. The people are spaced 1 m apart. When they enter the building it is dark so they slow down. There will be a back up of people at the door unless the people inside get closer to each other as they move through the building.