Question

In a biprism experiment, red light of wavelength 6500 Å was used. It was then replaced by green light of wavelength 5200 Å. The value of n for which (n + 1)^th green bright band would coincide with n^th red bright band for the same setting is ______.

Options

• n = 2

• n = 3

• n = 4

• n = 5

Answer 1

In a biprism experiment, red light of wavelength 6500 Å was used. It was then replaced by green light of wavelength 5200 Å. The value of n for which (n + 1)^th green bright band would coincide with n^th red bright band for the same setting is n = 4.

Explanation:

λ_R = 6500 Å  λ_G = 5200 Å

`beta = (lambda"d")/"D"`

(n + 1)λ_G = nλ_R 

(n + 1) × 5200 = n × 6500

`("n + 1")/"n" = 65/52`

`1/"n" = 65/52 - 1 = (65 - 52)/52 = 13/52 = 1/4`

∴ n = 4