Question

Two coherent monochromatic light beams of intensities $I$ and $4I$ are superposed. The maximum and minimum possible intensities in the resulting beam are

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

Answer 1

Answer: (C)

To find the intensity due to interference of two waves whose intensities are know, first find the amplitude of each wave $(\propto \sqrt{intensity}).$ Then find the amplitude due to superposition, using the phase difference between the waves. The square of this amplitude gives the intensity due to interference.