Question

In YDSE, the phase difference between two coherent sources is $\pi /3$ and constant. The intensity at a point, which is at equal distance from the sources is ? ($l_0$ is maximum intensity)

• A. $\frac{\sqrt{3}}{2}{l}_0$
• B. $\frac{l_0}{\sqrt{2}}$
• C. $\frac{1}{2}{l}_0$
• D. $3l_0$

Answer 1

The correct option is A $\frac{\sqrt{3}}{2}{l}_0$

Given

$\theta =\frac{\pi }{3}$

We know that intensity at point $P$ is

$I_p=I_{0}cos\frac{\theta }{2}$

Substitute all value in above equation

$I_p=I_{0}cos\frac{\pi /3}{2}=I_{0}cos\frac{\pi }{6}=I_0\times \frac{\sqrt{3}}{2}=\frac{\sqrt{3}{I}_0}{2}$

Correct option is A.