In the figure below, P and Q are two equally intense coherent sources emitting radiation of wavelength 20 m . The separation between P and Q is 5 m and the phase of P is ahead of that of Q by 90 ° . A , B and C are three distinct point of observation, each equidistant from the midpoint of PQ. The intensities of radiation at A , B , C will be in the ratio :

Step-by-step solution

Δ P A = π 2 × 20 2 π - 5 = 0     so  Δ ϕ A = 0 Δ P B = π 2 × 20 2 π = 5     so  Δ ϕ B = π 2 Δ P C = 5 + 5 = 10     so  ∆ ϕ c = π I = locos 2 Δ ϕ 2 so I A = I 0 I B = I 0 2  Ic  = 0 so  IA  : I B : I C = 2 : 1 : 0