Question

In a Young's doubleslit experiment, first maxima is observed at a fixed point P on the screen. Now, the screen is continuously moved away from the plane of slits. The ratio of intensity at point P to the intensity at point O (centre of the screen)

• A. remains constant
• B. keeps on decreasing
• C. first decreases and then increases
• D. first decreases and then becomes constant

Answer 1

The correct option is C first decreases and then increases

Position of $1^{st}$ Maxima:

$x=\frac{D\times \lambda }{d}$

As D increases, the Maxima at P will go upwards.

We know that There is a Minima between O and P.

Hence Point P will observe a decrease in intensity till the position of minima is reached and after that the Intensity will increase due to the Central Maxima.

Answer is C: first decreases and then increases