Two coherent monochromatic light beams of intensities I and 16 I, respectively, superimpose over each other. The resultant intensity in the constructive interference is
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( 25\,I \)
For coherent beams the amplitudes add, and the intensity is proportional to the square of the amplitude, \( I \propto a^{2} \), so \( a \propto \sqrt{I} \). In constructive interference the two amplitudes add directly.
\( \displaystyle I_{\max} = \left(\sqrt{I_1} + \sqrt{I_2}\right)^{2} = \left(\sqrt{I} + \sqrt{16I}\right)^{2} = \left(\sqrt{I} + 4\sqrt{I}\right)^{2} = 25\,I \)