Question

In a Young’s double slit experiment 12 fringes are observed to be formed on a certain segment of the screen when light of λ = 600 nm is used. If the wave length of light is changed to 400 nm, number off ringes observed in the same segment of the screen is

(a) 12

(b) 18

(c) 24

(d) 30

Answer 1

(b) 18

Let y be the length of the segment of screen considered. Let β₁ and β₂ be the fringe width for λ₁ = 600 nm and λ₂ = 400 nm respectively. Let n₁ and n₂ be the number of fringes of n₁ and n₂ observed. Obviously