Four harmonic waves of equal frequencies and equal intensities I0 have phase angles 0, π3, 2π3, and π. When they are superposed, the intensity of the resulting wave is nI0. The value of n is
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Solution
Let the amplitude of each wave is A.
The ones having phases of 0 and π will cancel each other.
Resultant of other two is having angle π3 between them is 2Acosπ6=√3A
Intensity I∝A2 ⇒I0=KA2
And, I=K(√3A)2=3KA2
So, I=3I0 ⇒n=3