Question

Two coherent sources are 1.8 mm apart and the fringes are observed on a screen 80 cm away from them. It is found that with a certain source of light, the fourth bright fringe is situated at a distance of 1.08 mm from the central fringe. Calculate the wavelength of light.

Answer 1

Data : d = 1.8 mm = 1.8 × 10^-3 m 

D = 80 cm = 0.8 m 

For fourth bright fringe, n = 4

y = 1.08 mm = 1.08 x 10^-3 m

For bright fringes, y = nλ \(\cfrac{D}d\)

This is the wavelength of light.