Question

(a) Draw ray diagram of refraction of light through a prism and explain the phenomenon of dispersion of light.
(b) Write the formula for lens power and define its unit.

Answer 1

(a) The dispersion of white light refers to its separation into different colour components. White light or visible light consists of the colours red, orange, violet, green, blue and yellow. This phenomenon can occur when white light travels through a glass prism. The white light that enters the prism is refracted at different angles, causing the separation of this light into the different colours. Each of these colours has a different wavelength. As the degree of refraction increases, the wavelength decreases. A shorter wavelength means that light bends more than at a longer wavelength. Red and orange light exhibits longer wavelengths, while blue or violet light has shorter ones. This results in forming a spectrum of seven colours while dispersion.

(b) Lens power $\left(P\right)=\frac{1}{focallengthoflens\left(f\right)}$

Its unit is dioptre (D), which is the reciprocal of metre (m).