In Young's double-slit experiment, 12 fringes are obtained on a certain segment of the screen when light of wavelength 600 nm is used. If the wavelength of light is changed to 400 nm , the number of fringes observed on the same segment of the screen is given by

Step-by-step solution

If on a certain segment of the screen, n 1 fringes of wavelength λ 1 are present and n 2 fringes of wavelength λ 2 are present, then n 1 β 1 = n 2 β 2 ⇒ n 1 λ 1 = n 2 λ 2 ∴ n 2 = n 1   λ 1 λ 2 = 12 × 600 400 = 18