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Question:

In an interference experiment the ratio of amplitudes of coherent waves is a_1/a_2 = 13. The ratio of maximum and minimum intensities of fringes will be

4

9

2

18

Solution:

Correct option is A. 4
Given a1/a2 = 1/3
Ratio of intensities, I1/I2 = (a1/a2)² = 1/9
Now, Imax/Imin = (√I1 + √I2)²/(√I1 - √I2)² = (1 + 3)²/(1 - 3)² = 4