Question

Coherent light of wavelength 500 nm passes through two slits that are placed a distance R from a screen. The slits are 0.05 mm apart. The first dark fringe occurs 1 cm from the central bright fringe. What is the distance R?

[A] 0.5 m [B] 0.667 m [C] 1 m [D] 2 m

Answer 1

Using

Where is the wavelength, a is the slit difference, and x is that the distance between dark and central fringe. Here, n is the no. Of fringe.

R is the distance between source and screen.

On substituting the value of  , a = 0.05 mm and x = 1 I'm = 0.01 mm.

We get, R = 1 m.