Question

Consider interference between waves from two sourceof intensities `I and 4 I`. Find intensities at points where phase difference is (i) `pi//2` (ii) `pi`.

Answer 1

We know `R^(2) = a^(2) + b^(2) + 2 ab cos phi`
`:. I_(R ) = I_(1) + I_(2) + 2 sqrt(I_(1)) sqrt(I_(2)) cos phi`,
In case (i), `phi = pi//2`
`:. I_(R ) = I + 4 I + 2sqrt(I xx 4 I) cos pi//2, I_(R ) = 5 I`
In case (ii), `phi = pi` ltbr. `:. I_(R ) = I + 4 I + 2sqrt(I xx 4 I) cos pi = I`