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 to $75\%$ of the initial value. Second minima is observed to be above this point and third maxima below it. Which of the following can be a possible value of phase difference caused by the mica sheet.

• A. $\frac{\pi }{3}$
• B. $\frac{13\pi }{3}$
• C. $\frac{17\pi }{3}$
• D. $\frac{11\pi }{3}$

Answer 1

The correct option is D $\frac{11\pi }{3}$

Here when second order minica replaces bright spot change in path difference$3\pi$

Second order minica phase difference$\frac{\pi }{2}$

Phase difference lies between $3\pi to4\pi$ i.e. $\frac{11\pi }{3}$