Bending Light

When light passes from one material to another it is not only the speed of the light that changes, the direction can change too.

If the ray of light is incident at 90° to the material then there is no change in direction, only speed.

It may help to imagine the front of the ray of light as the front of a car to determine the direction the light will bend. Imagine a lower refractive index as grass and a higher refractive index at mud.

Entering a Denser Material

The car travels on grass until tyre A reaches the mud. It is harder to move through mud so A slows down but B can keep moving at the same speed as before. The car now points in a new direction.

Denser material – higher refractive index – bends towards the Normal

Entering a Less Dense Material

The car travels in mud until tyre A reaches the grass. It is easier to move across grass so A can speed up but B keeps moving at the same speed as before. The car now points in a new direction.

Less dense material – lower refractive index – bends away from the Normal