Question

Assertion :Two point coherent sources of light $S_1$ and $S_2$ are placed on a line as shown in figure. $P$ and $Q$ are two points on that line. If at point $P$ maximum intensity is observed, then maximum intensity should also be observed at $Q$. Reason: In the figure, the distance $|S_{1}P-S_{2}P|$ is equal to distance $|S_{1}Q-S_{2}Q|$

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

For constructive interference, path difference between interfering beams= $n\lambda$.

Here for constructive interference at point P, $|S_{1}P-S_2|=n\lambda$

At point Q, $|S_{1}Q-S_{2}Q=|S_{1}P-S_{2}P|=n\lambda$

Hence waves interfere constructively at Q.