Question

Assertion :For the situation shown in figure, two identical coherent light sources produce interference pattern on the screen. The intensity of minima nearest to $S_1$ is not exactly zero. Reason: Minimum intensity is zero, when interfering waves have same intensity at the location of superposition.

• 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 Reason is correct

Answer 1

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

Resultant intensity at a point due to superposition of two waves of intensity $I_1,I_2$ at the point is given by,

$I=I_1+I_2+2\sqrt{I_1{I}_2}cos\delta$

For minima, $\delta =\pi$

Hence, $I=(\sqrt{I_1}-\sqrt{I_2}{)}^2$

But at the point of minima, the path travelled by two waves would be different. So they would have difference amplitudes at that point, and so the intensities.

Resultantly the intensity of the superposition would be finite.