Question

A monochromatic point source of light is placed at a distance $d$ from a metal surface. Photo electrons are ejected at a rate $n$ per second, and with maximum kinetic energy $E$. If the source is brought nearer to distance $d/2$, the rate and the maximum kinetic energy per photoelectron become nearly

• A. $2n$ and $2E$
• B. $4n$ and $4E$
• C. $4n$ and $E$
• D. $n$ and $4E$

Answer 1

Answer: (C)

Intensity $\propto \frac{1}{d^2}$
So when the source of light is brought closer
Intensity becomes $4$ times.
Hence, rate $\propto$ Intensity the rate will become $4n$.
$K{E}_{\max }$ depends on incident frequency which does not change and will remain $E.$