Describe an experiment to demonstrate transverse nature of light.

Explanation

(1) Young allowed a beam of sunlight to pass through a pinhole S into a dark room. The light emerging through S was allowed to pass through two more pinholes `S_(1)` and `S_(2)`, very close to each other and arranged symmetrically with respect to S.
(2) A screen was placed at a large distance from `S_(1)` and `S_(2)` and parallel to `S_(1)S_(2)` as shown in the figure.

(3) Light waves from `S_(1)` and `S_(2)` interfere at various points on the screen. white light is composed of waves of different wavelengths corresponding to various colours. Hence, the interference pattern on the screen consists of coloured bands (or fringes) of varying intensity. The central band at P is white and has maximum intensity.
(4) If monochromatic light is used, alternate bright and dark bands are obtained with the central band bright.
Importance of the experiment :
(1) It was the first experiment in which the interference of light was observed.
(2) It showed that light is propagated in the form of waves.
(3) It allowed the determination of the wavelength of monochromatic light.