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.

Explanation

Here, `lambda_(1)=630 nm=630xx10^(-9) m, beta_(1)=8.1 mm = 8.1xx10^(-3) m`
`lambda_(2)=?, beta_(2)=7.2 mm=7.2xx10^(-3) m`
Let d be the slit width and D be the distance between slit and screen, then
`beta_(1)=(lambda_(1)D)/d` and `beta_(2)=(lambda_(2)D)/d" ":. beta_(1)/beta_(2)=(lambda_(1)D)/d xx d/(lambda_(2)D)=lambda_(1)/lambda_(2)`
`(8.1xx10^(-3))/(7.2xx10^(-3))=(630xx10^(-3))/lambda_(2) implies 8.1/7.2=(630xx10^(-9))/lambda_(2)`
`:. lambda_(2)=(7.2xx630xx10^(-9))/8.1`
`=560xx10^(-9) m=560 nm`.
When the monochromatic source is replaced by a source of white light, the fringe width is changed.