Coherence Maintains Constant Phase Difference

Steps:

• Coherent waves have a fixed phase relationship over time.
• This fixed relationship means the phase difference between them remains constant.
• At point Z, the two waves arrive with this unchanging phase offset.
• A constant non-zero phase difference directly follows from coherence.

Why B is correct:

• Coherence is defined as waves with a constant phase difference, allowing stable interference patterns.

Why the others are wrong:

• A: Path length difference can vary; coherence concerns phase, not fixed paths.
• C: Coherence requires identical frequencies, so no non-zero frequency difference.
• D: Coherence relates to phase, not amplitude, which can differ without affecting coherence.

Final answer: B