Page 8 - Topic 3

WAVE/ LIGHT TERMINOLOGY

COHERENCE

Coherent wave sources are wave sources that maintain a constant phase relationship with each other.

This means that they must therefore have the same frequency.

There are two ways of producing coherent light sources.

1. By dividing the same light source
2. By using a laser – the light from a laser is perfectly coherent.

MONOCHROMATIC LIGHT

Monochromatic light is light that is of one colour only. This implies that it is of one frequency. Therefore if light is
coherent then it is monochromatic.

Examples

INCANDESCENT LIGHT

Incandescent light is light of many different frequencies. It is often seen as white light
(because white is the amalgam of all the colours). The emitted waves are not in phase
or coherent.

This type of light is usually from a source that is heated.

Examples