Dispersion of white light

White light is a mixture of visible colours. When it passes through a glass prism, the light changes direction as it enters and leaves the glass. This change of direction is called refraction.

The colours are refracted by different amounts, so they spread out after passing through the prism. This separation of white light into a visible spectrum is called dispersion. Violet light is deviated most from its original direction, while red light is deviated least.

Order of colours in the spectrum

The traditional seven colours, in order of increasing frequency, are:

Red → orange → yellow → green → blue → indigo → violet

In the same medium, frequency and wavelength are inversely related: a higher frequency corresponds to a shorter wavelength. The same sequence is therefore also the order of decreasing wavelength.

Red has the lowest frequency and longest wavelength; violet has the highest frequency and shortest wavelength.

Monochromatic light

Monochromatic light is light with a single frequency. Frequency describes how many oscillations of the light wave occur each second.

In a given medium, monochromatic light has a single corresponding wavelength: the distance between successive wave peaks. Its wavelength can be different in a different medium.

Monochromatic light differs from white light, which contains a mixture of visible frequencies rather than a single frequency.