COLOUR OF LIGHT

Colours of the rainbow from highest frequency to lowest:

• violet
• indigo
• blue
• green
• yellow
• orange
• red

However, when light enters a material medium, the speed is lesser and different for different colours!

Important
In a vacuum, all different frequencies of light have the same speed.
In a material medium, different frequencies have different speeds.

This is confirmed by refraction.
Violet light (shortest wavelength) is refracted more than red light.
Violet light travels slower than red light.

When light travels from one medium to another:

• the speed and wavelength changes
• but the frequency remains constant.

Thus a light wave is better described by it’s frequency, since the frequency stays the same whether the light is travelling through a vacuum or through a material medium.