Which is the KEY physical difference between interference and diffraction?
AInterference does not require coherence; diffraction does
BThere is no strict difference — both arise from superposition. Conventionally, with few sources (e.g., two slits) we call it 'interference'; with a continuous distribution (or one slit), 'diffraction' (per Feynman)
CDiffraction is observed only with sound, not light
DInterference requires opaque obstacles; diffraction does not
Answer & Solution
Correct answer: B. There is no strict difference — both arise from superposition. Conventionally, with few sources (e.g., two slits) we call it 'interference'; with a continuous distribution (or one slit), 'diffraction' (per Feynman)
Per **Feynman**: 'No one has ever been able to define the difference between interference and diffraction satisfactorily. It is just a question of usage.' Both are wave superposition phenomena. Convention: **few sources (e.g., 2-slit) = interference**; **many/continuous distribution (e.g., 1 wide slit) = diffraction**.
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