Question

A parallel beam of monochromatic light is incident normally on a narrow slit. A diffraction pattern is formed on a screen placed perpendicular to the direction of the incident beam. At the first minimum of the diffraction pattern, the phase difference between the rays coming from the two edges of the slit is :

• A. zero
• B. $\frac{\pi }{2}$
• C. $\pi$
• D. $2\pi$

Answer 1

The correct option is D $2\pi$

The phase difference between the rays coming from the two edges of the slit is given by the formula

$\frac{2\pi }{\lambda }dsin\theta$

where, d is the width of the slit.

the first minimum occurs when the following condition is satisfied

$sin\theta =\frac{\lambda }{d}$

$\therefore \frac{2\pi }{\lambda }d\frac{\lambda }{d}$

$=2\pi$