Question

Draw a diagram showing that white light can be dispersed and then recombined by using two similar equilateral prisms.

Answer 1

Place the first prism with its base downwards so that white light is dispersed into a spectrum. Then place the second identical prism inverted, with its base upwards, so that the refracting faces are opposite to the first prism.

• The first prism bends violet more than red, producing dispersion.
• The second prism produces an equal and opposite deviation for each colour.
• The colours recombine and emerge as white light.

This experiment shows that white light is composed of the seven colours of the visible spectrum.