For two sources to produce a steady, observable interference pattern they must be
Correct answer: B. coherent, keeping a constant phase relationship
- A. of different frequencies
- B. coherent, keeping a constant phase relationship
- C. very far apart
- D. of unequal amplitude
Explanation
If the phase difference between the sources drifts, the positions of the bright and dark fringes shift too fast to be seen and the pattern washes out. Coherence in practice means the same frequency and a fixed phase relationship, which is why Young used a single source split into two rather than two separate lamps. Equal amplitudes are not required, but they give the greatest contrast.
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About Superposition and Interference
Superposition states that overlapping waves produce a resultant displacement equal to the algebraic sum of their individual displacements. Interference covers constructive and destructive interference, phase difference, path difference, coherent sources, and conditions for maxima and minima. It differs from diffraction, which involves spreading around openings or obstacles.
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