Question

Interference fringes are obtained due to the interference of waves from two coherent sources of light with amplitudes $a_1$ and $a_2(a_1=2a_2)$. What is the ratio of the maximum and minimum intensities of light in the interference pattern?

• A. $2$
• B. $4$
• C. $9$
• D. $\infty$

Answer 1

The correct option is C $9$

amplitudes are $a$ and $2a$ hence intensities are in the ratio $a^2:(2a{)}^2=1:4$
let their intensities be $I$ and $4I$
maximum intensity is $(\sqrt{I}+\sqrt{4I}{)}^2=9I$
minimum intensity is $(\sqrt{I}-\sqrt{4I}{)}^2=I$
ratio is $9:1$
option $C$ is correct