Q. 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
Explanation
(d) Since $P$ is ahead of $Q$ by $90{^\circ}$ and path difference between $P$ and $Q$ is $\lambda/4$. Therefore at $A$, phase difference is zero, so intensity is $4I$. At $C$ it is zero and at $B$, the phase difference is $90{^\circ}$, so intensity is $2I$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.