Question

Assertion :Three waves of equal amplitudes interfere at a point. Phase difference between two successive waves is $\frac{\pi }{2}$, Then resultant intensity is same as the intensity due to individual wave. Reason: For interference to take place source must be coherent.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct

Answer 1

The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

Three waves of same amplitude interfere at a point, the phase difference between consecutive waves is $\frac{\pi }{2}$
I.e. phase difference between first and third is $\pi$ these two will destructively interfere to give a wave of 0 amplitude which superimposed with the second wave, gives us a wave of just amplitude A.
The vital condition for interference to take place is coherence.
Hence both assertion and reason are true, but reason is not the correct explanation.
Option B is correct.