Fig, here shows P and Q as two equally intense coherent sources emitting radiations of wavelength 20m. The separation PQ si 5m, and phase of P is ahead of the phase Q by `90^(@)`. A, B and C are three distant points of observation equidistant from the mid - point of PQ. The intensity of radiations of A, B, C will be in the ratio

Options

A. (a) `0:1:4`
B. (b) `4:1:0`
C. (c) `0:1:2`
D. (d) `2:1:0`

Answer

D

Explanation

Since P is ahead of Q by `90^@` and path difference between P and Q is `lambda//4`. Therefore at A, phase difference is zero, so intensity is `4I`. At C it is zero and at B, the phase difference is `90^@`, so intensity is `2I`.