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If the phase difference between the two waves producing interference is 13π rad, then ______ order ______ interference occurs.

Asked in GSEB Board July 2022 · Intensity and coherent sources

Answer: (3) 7th, destructive

Step-by-step solution

Given: phase difference Δφ=13π rad between the two interfering waves.

Idea: constructive interference needs an even multiple of π, Δφ=2nπ; destructive interference needs an odd multiple, Δφ=(2n-1)π, and the n in that formula is the order.

13π is an odd multiple of π, so the interference is destructive.

Now match the order: 2n-1=13.

n=7.

In path terms Δ x=λ/(2π)×13π=6.5λ, an odd number of half wavelengths -- a dark point, of the seventh order.

Why the other options are wrong

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