Refraction

What is Refractio

nRefraction is the bending of a wave when it passes from one medium to another at an angle & therefore changes speed.

Why does light bend?

The wheel that strikes the grass first slows first, causing the direction to change.

Part of the wave strikes the surface first and therefore slows first, causing the direction to change.

Don’t forget…

Sand

PavementAir

Glass

3 x 108 m/s

3 x 108 m/s

2 x 108 m/s

vs < vp

Light speeds back up if entering into a less dense

medium.

The Amount of Bending…

The change in speed depends (and amount of bending) on the differences in density between the mediums.

Refraction Distorts Vision

Water

Air

Water

Air

The eye, believing that light travels in straight lines, sees objects closer to the

surface due to refraction. Such distortions are common.

Water

Air

refraction

N

qw

qA

Note: the angle of incidence qA in air and the angle of refraction qw

in water are each measured with the normal N.

The incident and refracted rays lie in the same plane and are reversible.

The Index of RefractionThe index of refraction for a material is the ratio of the velocity of light in a vacuum (3 x 108 m/s) to the velocity through the material.

Index of refractioncn

v

c

vc

nv

Some common index of refractions

Medium Index

Vacuum 1.00

Air 1.00029

Water 1.333

Crown Glass

1.52

Diamond 2.419

In general, the greater the index of refraction for a medium, the slower light travels in that medium.

Example 1. Light travels from air (n = 1) into glass, where its velocity reduces to only 2 x 108 m/s. What is the index of

refraction for glass?vair = c

vG = 2 x 108 m/s

Glass

Air

For glass: n = 1.50

n =

n =

Speed changes…

This bends the light…

As light goes from medium to medium…

The amount of bending depends on the index of refraction.

1

2

n2

n1

n1= n2

1

2

n2

n1

n2 > n1

1

2

n2

n1

n1 > n2

same speed as thenext, it doesn’t bend

fast into slow,it will bends in toward normal.

slow into fast, it will bends away from normal.

click

ExamplesObject appear higher in water since water has a greater index of refraction than

air.

Snell’s Law

2211 sinsin nn

n1

n2

1

2

Some TerminologyAngles are measured with respect to the line which is perpendicular to the interface, called the normal.

The angle the incident (incoming) ray makes with the normal is called the angle of incidence (1).

The angle the refracted ray makes with the normal is called the angle of refraction (2).

Fiber Optics- pure glass fibers used for the fastest data transmission through

pulses of light that are internally reflected

Dispersion: The process of separating polychromatic light into it’s component wavelengths.

Atmospheric Refraction-the refraction of the sun’s rays through layers of the

Earth’s atmosphere, permitting light to

be seen even after the sun has set.

Mirages-produced by the bending of light rays in the atmosphere when there are large temperature differences between the

ground and the air.

Rainbows

An observer sees red light coming from droplets of water higher in the sky, while droplets of water lower in the sky send violet light to the eye.