In YDSE a parallel beam of incident light consists of two wavelengths λ 1 = 4000 A ∘ and λ 2 = 5600 A ∘ . The minimum distance y on the screen, measured from the central axis, where the bright fringe due to two wavelengths coincide is n λ 1 D d . Find n .

Step-by-step solution

n 1 X ¯ 1 = n 2 X ¯ 2 n 1 D λ 1 d = n 2 D λ 2 d n 1 λ 1 = n 1 λ 2 λ 1 λ 2 = n 2 n 1 = 4000 5600 = 40 58 = 5 7 ∴ n 2 n 1 = 5 7 ⇒ X 1 X 2 = 7 5 ∴ y = 7 X ¯ 1 = 7 D λ 1 d