Question

Two sources of light are said to be coherent when both give out light waves of the same

• A. amplitude and phase
• B. intensity and wavelength
• C. speed
• D. wavelength and a constant phase difference

Hint:

Coherent sources are essential for interference — they must have the same wavelength and a constant phase difference to produce a steady interference pattern.

Answer 1

The Correct Option is D

For two light sources to be coherent, they must emit waves having the same wavelength and maintain a constant phase difference over time.
This ensures stable and observable interference patterns.
Amplitude, speed, or intensity can differ, but coherence strictly requires a fixed phase relationship.