In Young's Double Slit experiment, the intensities of two coherent monochromatic waves are I and 4I. The ratio of intensity at maxima to minima will be:

9 : 1

The correct answer is Option (4) → 9 : 1

$I_{max}=\left(\sqrt{I_1}+\sqrt{I_2}\right)^2$

$I_{min}=\left(\sqrt{I_1}-\sqrt{I_2}\right)^2$

$∴I_{max}=\left(2\sqrt{I_1}+\sqrt{I_2}\right)^2=9I$

$I_{min}=\left(2\sqrt{I_1}-\sqrt{I_2}\right)^2=I$

$∴\frac{I_{max}}{I_{min}}=\frac{9}{1}$