Question

Figure here shows P and Q as two equally intense coherent sources emitting radiations of wavelength 20 m. The separation PQ is 5.0 m and phase of P is ahead of the phase of Q by ${90}^{\circ }$. A, B and C are three distant points of observation equidistant from the mid-point of PQ. The intensity of radiations at A, B, C will bear the ratio

• A. 0 : 1 : 4
• B. 4 : 1 : 0
• C. 0 : 1 : 2
• D. 2 : 1 : 0

Answer 1

The correct option is D 2 : 1 : 0

Since P is ahead of Q by ${90}^{\circ }$ and path difference between P and Q is $\frac{\lambda }{4}$. Therefore at A, phase difference is zero, so intensity is 4I. At C it is zero and at B, the phase difference is ${90}^{\circ }$, intensity is 2I.