The distance between two coherent sources is 1 mm. The screen is placed at a distance of 1 m from the sources. If the distance of the third bright fringe is 1.2 mm from the central fringe, the wavelength of light used is

Step-by-step solution

The position of maxima y n = n D λ d ⇒ λ = y n d n D Here, n = 3 , y n = 1.2 m m = 1.2 × 10 - 3 m , D = 1 m , d = 1 m m = 1 × 10 - 3 m ∴ λ = 1.2 × 10 - 3 × 1 × 10 - 3 3 × 1 = 0.4 × 10 - 6 m = 4 × 10 - 7 m = 4000 Å