Question

White light is used in a Young's double slit experiment. Find the minimum order of the violet fringe (λ= 400 nm) which overlaps with a red fringe (λ= 700 nm).

Answer 1

Let m^th bright fringe of violet light overlaps with n^th bright fringe of red light.

=> 7^th bright fringe of violet light overlaps with 4^th bright fringe of red light (minimum). Also, it can be seen that 14^th violet fringe will overlap 8^th red fringe.
Because, m/n = 7/4 = 14/8.