Concept:For two wave sources to produce a stable, sustained, and meaningful interference pattern (either perfectly constructive or perfectly destructive in space), they must be
coherent.
Solution:- Coherence strictly requires the two interacting waves to have the exact same frequency and a constant phase difference.
- If waves have different frequencies, they will constantly drift in and out of phase. They will alternately undergo moments of constructive and destructive interference (creating a phenomenon known as "beats").
- Because none of the options provide a pair of identical frequencies (e.g., 20 Hz and 20 Hz), none of them can form a stable, spatial pattern of pure constructive interference. Hence, None of these is the correct scientific conclusion.
Why other options are incorrect:Options A, B, and C all present mismatched frequency pairs. These pairs will produce beats (throbbing amplitude over time) rather than a fixed spatial interference pattern.
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