A beam of light consisting of two wavelengths, 650 nm and 520 nm, is used to obtain interference fringes in a Young's double-slit experiment.
Find the distance of the third bright fringe on the screen from the central maximum for wavelength 650 nm.

Explanation

Here, `lambda=650m=650 xx 10^(-9)m, lambda_(2)=520nm=520 xx 10^(-9)m`
Supose `d="Distance between two slits, D=Distance of screen from the slits"`
Let `n^(th)` fringe due to `lambda_(2)=520nm` coincide with `(n-1)^(th)` bright fringe due to `lambda_(1)=650nm`
`therefore nlambda_(2)=(n-1)lambda, nxx520 =(n-1) 650, 4n=5n-5 or n=5`
`therefore` The least distance required `x=nlambda D/d=5xx520 (D)/(d)=2600 (D)/(d)nm`