Question

Two coherent monochromatic beams of intensities $I$ and $4I$ respectively are superimposed. The maximum and minimum intensities in the resulting pattern are

• A. 5I and 3I
• B. 9I and 3I
• C. 4I and I
• D. 9I and I

Answer 1

The correct option is D 9I and I

The maximum intensity due to combination of two coherent monochromatic beams of intensities $I_1$ and $I_2$ are $(\sqrt{I_1}+\sqrt{I_2}{)}^2$ and $(\sqrt{I_1}-\sqrt{I_2}{)}^2$.

Hence the maximum and minimum intensities are $(2\sqrt{I}+\sqrt{I}{)}^2$ and $(2\sqrt{I_1}-\sqrt{I_2}{)}^2$, that are $9I$ and $I$ respectively.