Incoherent sources and interference – Rankers Physics

Young's Double Slit Experiment: Practice Problem & Solution

Assertion (A): Incoherent sources do not produce an interference pattern. Reason (R): Light from two coherent sources that are not in phase does not produce an interference pattern.  
Both (A) & (R) are true and the (R) is the correct explanation of the (A)
Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(A) is true but (R) is false
Both (A) and (R) are false

Short Solution (Best for NEET):

To solve this problem, we apply the core principles of Young's Double Slit Experiment. Understanding the underlying formula is key to arriving at the correct answer below:

Assertion (A) is true: Incoherent sources have rapidly fluctuating phase differences, resulting in an average uniform intensity rather than a stable interference pattern.

Reason (R) is false: Coherent sources, even if not in phase (i.e., having a constant non-zero phase difference), will still produce a stable interference pattern, though its position might shift. Hence, (A) is true, (R) is false.

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