Question

In a YDSE with two identical slits, when the upper slit is covered with a thin, perfectly transparent sheet of mica, the intensity at the centre of screen reduces from its initial value. Second order minima is observed to be above this point and second order maxima below it. Which of the following can not be a possible value of phase difference caused by the mica sheet?

• A. $\frac{\pi }{3}$
• B. $\frac{7\pi }{2}$
• C. $\frac{10\pi }{3}$
• D. $\frac{11\pi }{3}$

Answer 1

Answer: (B)

$\frac{7\pi }{2}$

When $2nd$ order minima replace central bright spot change in path differ =$3\pi$
as $2nd$ order minima just goes about the central phase difference =$\frac{\pi }{2}$
Net phase differ = $3\pi +\frac{\pi }{2}$
= $\frac{7\pi }{2}$

Hence the option (B) $\frac{7\pi }{2}$ is correct.