Answer:
Explanation:
Let λ be the required wavelength.
Two fringe patterns will be formed on the screen which will overlap each other. Let 9 th bright fringe of first coincides with 11 th bright fringe of second.
position of 9 the bright fringe of first = 9x 646 x D/d nm
position of 11 th bright fringe of second pattern = 11 x λ x D/d
now , 9 x 646 = 11 x λ
λ = 9 x 646 / 11 = 528.54 nm.