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In the figure given below, P and Q are two equally intense coherent sources emitting radiations of wavelength 20 m. The separation between P and Q is 5.0 metre and phase of P is ahead of the phase of Q by 90^(@), A, B and C are three distant points of observation, equidistant from the mid point of PQ.The intensity of radiation at A, B, and C will bear the ratio : |
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Answer» ` 0 : 1 : 4`  Path difference PQ = 5m = `(lambda)/(4)` So PHASE difference = `lambda /4 xx (2 pi)/(lambda) = (pi)/(2)`. Initial phase at P is `(pi)/(2)` so, phase difference between P and Q w.r.t A is zero. Net phase difference between P and Q w.r.t B = `(pi)/(2)`. Net phase difference between P and Q w.r.t `C = (pi)/(2)`. `THEREFORE I_(A) = I + I + 2 sqrt I.Icos 0^(@) = 4 I` `I_(B) = I + I + 2 sqrt I.I cos 90^(@) = 2I` `I_(C) = I + I + 2 sqrt I.Icos 180^(@) = 0` `therefore Ratio I_(A) : I_(B) : I_(C) :: 2 : 1 : 0` |
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