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

Explanation

`triangle phi " at "A= 0 therefore I= 4I_(0)`
`triangle phi " at "B= (pi)/(2)," "therefore I= 2I_(0)" "triangle phi " at "C= pi, "" therefore I= 0`
ratio `2 : 1 : 0`.