Question

A point source causes photoelectric effect from a small metal plate. Which of the curves in fig. may represent the saturation photo-current as a function of the distance between the source and the metal?

• A. A
• B. B
• C. C
• D. D

Answer 1

The correct option is D D

Solid angle subtended by the metal plate for the point charge is: $\frac{4\pi }{r^2}$.

So as the distance between the source and the metal increase the solid angle will decrease, which will reduce the number of photon incident on the surface. And eventually decrease the photocurrent. So, the curve will be a rectangular hyperbola.