Question

Two sources of monochromatic light are coherent when their:

• A. intensities are equal
• B. amplitudes are equal
• C. phases are equal
• D. none of these

Hint:

Coherent sources must maintain a constant phase relationship.

Answer 1

The Correct Option is C

Two light sources are said to be coherent if they maintain a constant phase difference over time. This means the waves emitted by these sources oscillate in step with each other, usually having the same frequency and a fixed phase relationship. Coherence is essential for producing a stable and visible interference pattern because fluctuating phase differences would cause the pattern to blur or disappear. Therefore, coherent sources have: \[ \text{Constant phase difference} \quad \Rightarrow \quad \text{Stable interference fringes}. \]