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If two waves having amplitudes a and b make superposition the resultant amplitude A is given as A = 1 √(a^2 + b^2 + 2ab cosφ) where φ is phase constant. The intensity (I)2 is directly proportional to square of amplitude. I α A^2 I.e. I α (a^2 + b^2 + 2ab cos φ )

In case of constructive interference cos φ = 2np. Imax = k (a + b)^2
While in case of destructive interference Imax = k (a – b)^2
Light wave from two coherent sources of intensity ratio 81 : 1 produce interference. Using these information
choose correct answer in the following.

1. The ratio of maxima and minima in the interference pattern is.
a) 9:1 b) 81 : 1 (C) 25 : 16 (D) 16 : 25

2. The ratio of amplitudes of light waves from two sources is
(A) 1 : 4 (B) 4 : 1 (C) 2 : 1 (D) 1 : 2

3. (The ratio of amplitudes of two sources is
(A) 9 : 1 (B) 81 : 1 (C) 1 : 9 (D) 1 : 81