Question

Consider the diffraction pattern obtained from the sunlight incident on a pinhole of diameter $0.1\text{µm}$. If the diameter of the pinhole is slightly increased, it will affect the diffraction pattern such that:

• A. its size decreases, but intensity increases
• B. its size increases, but intensity decreases
• C. its size increases and intensity increases
• D. its size decreases and intensity decreases

Answer 1

The correct option is A its size decreases, but intensity increases

For diffraction through a single slit, for first minimum.
$\sin \theta =\frac{1.22\lambda }{D}$

If $D$ is increased, then $\sin \theta$ will decrease, i.e $\theta$ will decrease.
$\therefore$ size of circular fringe will decrease, but intensity increases.