Two needles bob in a water trough with a phase difference that never changes. The sources are:
ADiffracted
BCoherent
CIncoherent
DPolarised
Answer & Solution
Correct answer: B. Coherent
1. The needles move up and down in step.
2. Their phase difference is fixed in time.
3. Such sources are coherent.
_Source: NCERT Class 12 Physics Part II, Chapter 10, Wave Optics._
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