Coherent sources have:
- Constant phase difference (and same frequency)
- Different frequencies
- Different wavelengths
- Random phases
Show answer and solution
Correct answer: A. Constant phase difference (and same frequency)
**Coherent:** same frequency AND constant (typically zero) phase difference.
Required for stable interference pattern.
Lasers are highly coherent.
Two independent bulbs are incoherent (no fixed phase relation).