Coherent sources are those that emit waves of
A{'text': 'Same frequency AND a constant phase difference in time', 'label': 'A'}
B{'text': 'Same intensity only, without any relationship of frequencies', 'label': 'B'}
C{'text': 'Same wavelength only, regardless of the phase behaviour', 'label': 'C'}
D{'text': 'Different frequencies but a similar overall intensity level', 'label': 'D'}
Answer & Solution
Correct answer: A. {'text': 'Same frequency AND a constant phase difference in time', 'label': 'A'}
1. Sustained interference requires coherent sources.
2. Coherent sources emit waves with the same frequency (wavelength).
3. They must also maintain a constant phase difference over time.
4. Two independent light bulbs are not coherent; a laser output is.
_Source: NCERT Class 12 Physics, Ch 10 "Wave Optics", §10.4_
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