In Young's double slit experiment , two wavelengths `lamda_1 = 780 nm ` and `lamda_2 = 520` nm are used to obtain interference fringes. If the `n^(th)` bright band due to `lamda_1` coincides with `(n+1)^(th)` bright band due to `lamda_2`, then the value of n is

Options

A. 4
B. 3
C. 2
D. 6

Answer

C

Explanation

As `n^(th)` bright band due to `lamda_1` coincides with `(n+1)^(th)` bright band due to `lamda_2`
or `nlamda_1 = (n+1) lamda_2`
or `n/(n+1)=lamda_2/lamda_1=(520 nm)/(780 nm) =2/3`
or `3n = 2n +2 " or " 3n - 2n = 2 " or "n = 2`