In Young's double Slit experiment $3^{rd}$ maxima (Bright Band) is obtained at a distance $d_1$ from the central bright fringe when light of wavelength $\lambda_1$ is used and at a distance $d_2$ when light of wavelength $\lambda_2$ is used. What will be the ratio of $d_1$ and $d_2$?

$\frac{\lambda_1}{\lambda_2}$

The correct answer is Option (3) → $\frac{\lambda_1}{\lambda_2}$

Distance of n^th maxima from the central bright fringe

$x=\frac{n \lambda D}{d}$

$x_3=\frac{3 \lambda D}{d}=d_1$           ......(i)

$x'_3=\frac{3 \lambda_2 D}{d}=d_2$           ......(ii)

$\frac{d_1}{d_2}=\frac{\lambda_1}{\lambda_2}$