Question

The intensity of the light coming from one of the sites in a Young's double slit experiment in the intensity from the other slit. Determine the ratio of the maximum intensity to the minimum intensity in the interference fringe pattern observed.

Answer 1

The intensity of the light originating from the first slit is double the intensity from the second slit. The amplitudes of the two interfering waves are in the ratio $\sqrt{2}:1$ , say $\sqrt{2}A$ and $A$.

At the point of constructive interference, the resultant amplitude becomes $(\sqrt{2}+1)A$. At the points of destructive interference , this amplitude is $(\sqrt{2}–1)A$

The ratio of the resultant intensities at the maxima to that at the minima is

$\frac{(\sqrt{2}+1)A^2}{(\sqrt{2}-1)A^2}=3:4$