Question

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

(a) 12

(b) 18

(c) 24

(d) 30

Answer 1

Correct option (b) 18

Explanation:

Fringewidth  β =  λD/d

Let y is the segment on screen which contain 12 fringes of wavelength λ₁

∴ = y = 12β =  12(λ₁D/d)

Let N fringes of λ₂ occupy the same segment.