Refraction is the _________ of light when it enters a new medium / material.

For example: Light traveling from the cat to our eye must travel through glass and water. The resulting bending of the light in these new mediums produces a distorted image.

bending

So, what causes light to bend when it travels into a new medium?To see it, imagine an axle with two wheels that is rolling across a sidewalk and hits the grass . The wheel that hits the grass first ____________, causing the wheel to ______. (ever driven your car off onto a rough shoulder?)

slows down

turn

In a similar way, a wave that enters a new medium changes _______, which can cause the wave to bend….This is refraction. Which way will the light bend?

speed

WaterAir

Water

Air

Which way will the light bend?

WaterAir

Water

Air

Thin to thick = bends towards

Thick to thin = bends away

A person is standing on the edge of a lake spear fishing. This is where you use a spear to “poke” a fish. In order to “spear” a fish that he could see in a lake, where should he aim his spear?

(Above, at, or below where he sees the fish?)

Aim ________ where you see the fish!!BELOW

Stuff underwater is _______ than it looks!!

deeper

Actual fish

You see him here

So we know that different materials like water bend light at the interface (or where the materials meet).

The next question should be how much does light bend?

Introducing a man named Snell who was an astronomer and did the experiment to find out…

Snell’s Law, first worked out in 1621 by the Dutch astronomer, relates the angles to the “n” values…

11 sinn 22 sinn

“n” is called the index of refraction and is a measure of how “thick” a material is compared to vacuum.

Let’s do some Practice Problems

A beam of light is traveling through the air. It strikes our container of water at an angle of incidence (shown below) of 25o. What happens to the beam of light?

Air

25o

Water

n = 1.33

Water

25o

Air

n = 1.0

n = 1.33

A beam of light is traveling through the water. It strikes our container of air at an angle of incidence (shown below) of 25o. What happens to the beam of light?