What Is Light?: 12.1 What is Refraction?

January 2014

In the Light & Geometric Optics unit, we studied The Refraction of Light.

This is what we studied in Section 12.1.

In our textbook on page 515, refraction is defined like this:

refraction

the bending or change in direction of light

when it travels from one medium into another

Here is a another way to explain refraction:

REFRACTION is the bending of a path of light.

• A one-word synonym for refraction is bending. Light travels in straight lines.

A bend in its direction occurs when it travels from one material (or medium) into another.

• A light wave is refracted or bent at the boundary of the two mediums that it is travelling through. For this reason, refraction is called a boundary behaviour.

THE REFRACTION OF LIGHT GOING FROM AIR INTO WATER

WHAT CAUSES REFRACTION?

Different mediums have different densities. Density is the measure of how tightly packed the particles are in a substance. For example, air is less dense than water.

• The density of a material affects the speed of light and this in turn, affects the way the light bends so that refraction occurs.

THE RULES FOR REFRACTION

The speed of light changes depending on the medium through which the light is travelling. The light ray that is transmitted (travels through an object) is called

the refracted ray. The angle of refraction is the angle between the refracted

light ray and the normal.

RULE 1

• The incident ray, the refracted ray and the normal all lie in the same plane.

• The incident ray and the refracted ray are on opposite sides of the line or boundary that separates the two media.

RULE 2

• When light travels from one medium to another, the speed of light will either

speed up or slow down.

• When the speed of light is slower in the second medium, the refracted ray will

bend closer to the normal.

• When the speed of light is faster in the second medium, the refracted ray will

bend away from the normal.

LIGHT BENDS TOWARD THE NORMAL WHEN ITS SPEED DECREASES IN A MATERIAL

LIGHT BENDS IN PREDICTABLE WAYS

• When light travels into a medium that is denser, the light is slowed down and bends toward the medium and the angle of refraction gets smaller.

• When light travels into a medium that is less dense, the light speeds up and bends away from the medium and the angle of refraction gets bigger.

A COMMON EXAMPLE OF REFRACTION

When a spoon is placed in a glass of water and viewed from the

side, it appears to be broken or bent.This is due to the difference

in the refractive properties of air and water.

Since water is denser than air, the spoon appears to bend as the

light it reflects is slowed by the density of the water.

This phenomenon also makes submerged objects such as fish look

closer to the surface than they actually are.

PARTIAL REFLECTION AND REFRACTION

Refraction is often accompanied by reflection.

Some of the light that strikes water is reflected off the water, but a great deal of light is also refracted as it enters the water and illuminates the water below the surface.

THE TREE IS VISIBLE DUE TO REFLECTION. THE FISH ARE VISIBLE DUE TO REFRACTION.