The sunlight is allowed to fall on a pinhole of diameter $10^{-4}$ mm and thus a diffraction pattern is obtained. How will the size and intensity of the diffraction pattern be affected, if the diameter of the pinhole is slightly increased?

size decreases; intensity increases

The correct answer is Option (3) → size decreases; intensity increases

For a circular pinhole, diffraction pattern size is inversely proportional to the diameter of the pinhole:

Angular radius of central maximum: $\theta \approx 1.22 \frac{\lambda}{d}$

→ If diameter $d$ increases, $\theta$ decreases → diffraction pattern size decreases.

Also, intensity is proportional to the area of the pinhole ($\propto d^2$):

→ If $d$ increases, intensity increases.

∴ Correct option: size decreases; intensity increases.