In a YDSE with two identical slits, when the upper slit is covered with a thin, perfectly tranparent sheet of mica, the intensity at the centre of screen reduces ro `75%` of the initial value. The second minima is observed to above this point and third maxima below it. which of the following can not be a possible value of phase difference caused by the mica sheet

Options

A. `(pi)/(3)`
B. `(13pi)/(3)`
C. `(17pi)/(3)`
D. `(11pi)/(3)`

Answer

A

Explanation

`I'=(3)/(4)(4I)=3I`
So `4I=I+I+2Icosphiimpliescosphi=(1)/(2)impliesphi=(pi)/(3)`
But value should lie between `3pi` & `6pi`
So it cannot be `(pi)/(3)`
for second minima `phi=3pi`
for third maxima `phi=6pi`