Question

A parallel beam of monochromatic light is incident normally on a slit. The diffraction pattern is observed on a screen placed at the focal plane of a convex lens. If the slit width is increased, the central maximum of the diffraction pattern will

• A. become broader and fainter
• B. become broader and brighter
• C. become narrower and fainter
• D. become narrower and brighter

Answer 1

Answer: (D)

Width of central maximum
$\beta =\frac{D\lambda }{d},d$ being slit width.
If the slit width is increased the central maximum becomes narrower and more light reaches the region.