In Young's double slit experiment, in an interference pattern, third minimum is observed exactly in front of one of the slits. If ' d ' is the distance between the slits and ' D ' is the distance between the slits and the screen, the wavelength of light used is

Step-by-step solution

The position of the n -th minimum from the central maximum in Young's double slit experiment is given by: y_n = (2n - 1) D 2d For the third minimum, n = 3 : y₃ = (2(3) - 1) D 2d = 5 D 2d Since the third minimum is observed exactly in front of one of the slits, its distance from the central maximum is y = d 2 . Equating the two expressions for y : 5 D 2d = d 2 5 D = d^2 = d^2 5D Answer: d^2/5D