Two light beams of intensities in the ratio 25 : 9 are allowed to interfere. The ratio of the intensities of maxima and minima will be
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 16 : 1
In interference the amplitudes add (in phase at a maximum, in opposite phase at a minimum), and the intensity is proportional to the square of the amplitude.
\( \displaystyle \frac{a_1}{a_2} = \sqrt{\frac{I_1}{I_2}} = \sqrt{\frac{25}{9}} = \frac{5}{3} \)
\( \displaystyle \frac{I_{\max}}{I_{\min}} = \frac{(a_1 + a_2)^{2}}{(a_1 - a_2)^{2}} = \frac{(5 + 3)^{2}}{(5 - 3)^{2}} = \frac{64}{4} = \frac{16}{1} \)