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 $90^{\circ}$. $A, B$ and $C$ are three distinct points of observation, each equidistant from the midpoint of $P Q$. The intensities of radiation at $A, B, C$ will be in the ratio