Laser light of wavelength `630 nm` incident on a pair of slits produces an interference pattern where bright fringes are separated by `8.1 mm`. Another light produces the interference pattern, where the bright fringes are separated by `7.2 mm`. Calculate the wavelength of second light.

Answer

`560 nm` ; coloured fringes with white centre

Explanation

As `(lambda')/(lambda) = (beta')/(beta)`
`:. lambda' = (beta')/(beta) xx lambda = (7.2)/(8.1) xx 630 = 560 nm`
When monochromatic source is replaced by source of white light, fringes are coloured with white centre.