Refraction of light

Learning goals We are learning why light bends. We are learning to calculate the index of refraction.

the bending of light as it moves from one medium to another. Refraction the bending of light as it moves from one medium to another. Medium examples – air, water, oil, glass, etc.

Reflection occurs when light bounces off an object. Refraction occurs because light bends.

refraction

What is the speed of Light? Through air: 3.00 x 108 m/s Through water: 2.26 x 108 m/s i.e. light SLOWS down when moving through a denser medium

Drawing Refracted Rays normal - line drawn at right angle to boundary between two mediums at ray's entry point. angle of refraction - angle refracted light ray makes with normal inside material.

Determining refracted angle use a measurement called refractive index. a substance with a high refracted index is more dense and therefore light will travel slower through it (bends more). Common refractive indexes (see p. 524 for more examples) Material Refractive index Air 1.00 Pure water 1.33 Olive oil 1.49 Glass 1.52

Angle of Refraction Rules If light enters a slower medium (more dense), the refracted ray bends towards the normal. If light enters a faster medium (less dense), the refracted ray bends away from the normal.

Snell’s Law used to calculate the refractive index (n): Where: c = 3.0 x 108 m/s v = speed of light in medium i = angle of incidence R = angle of refraction n = refractive index

The Pencil Picture Why does the pencil appear bent in the water?

As light travels from the water into the air, the speed of light increases and the light therefore bends away from the normal Our brain doesn’t interpret this “bending” correctly so it projects the light rays backwards, making it look like the spoon has bent.

Example #1 What is the refractive index of material in which light travels at 2.5 x 108 m/s?

Example #2 How quickly would light travel in a material with a refractive index of 1.75?

Learning goals We are learning why light bends. We are learning to calculate the index of refraction.

Homework P519 #2-4 P.525 #2,3,6-8