Question

When two coherent monochromatic light beams of intensities I and 4 I are superposed, the ratio between maximum and minimum intensities in the resultant beam is :

• A. 9:1
• B. 1:9
• C. 4:1
• D. 1:4

Answer 1

The correct option is A 9:1

If Intensities are $I$ and $4I$ then amplitudes are in ratio of 1/2 because
amplitudes is square root of Intensity.
Let amplitudes be $x$ and $2x$ respectively.
At maxima amplitudes add up giving $3x$
At minima amplitudes substract giving $-x$
Thus maximum to minimum Intensity is 9:1 as Intensity is square of amplitude.