Two coherent monochromatic light beams of intensities I and 4I are superposed. The maximum and minimum possible intensities of the resulting beam will be
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 9 I and I
For coherent beams the amplitudes add, not the intensities, and intensity is proportional to the square of the amplitude, so \( a \propto \sqrt{I} \).
\( \displaystyle I_{\max} = \left(\sqrt{I_1} + \sqrt{I_2}\right)^{2} = \left(\sqrt{I} + 2\sqrt{I}\right)^{2} \)
\( \displaystyle I_{\max} = 9I \)
\( \displaystyle I_{\min} = \left(\sqrt{I_2} - \sqrt{I_1}\right)^{2} = \left(2\sqrt{I} - \sqrt{I}\right)^{2} \)
\( \displaystyle I_{\min} = I \)
Note: A similar question was also asked in CUET (UG) 2026 on 19-05-2026 (Slot 1), and in CUET (UG) 2023 on 09-06-2023 (Slot 3) and on 22-05-2023 (Slot 3).