Question

A photoelectric cell is illuminated by a point source of light 1 m away. When the source is shifted to 2 m then

• A. Number of electrons emitted is half the initial number
• B. Each emitted electron carries half the initial energy
• C. Number of electrons emitted is a quarter of the initial number
• D. Each emitted electron carries one quarter of the initial energy

Answer 1

The correct option is C

Number of electrons emitted is a quarter of the initial number

Number of electrons emitted $\propto$ intensity $\propto \frac{1}{(distance{)}^2}$
$\Rightarrow \frac{n_1}{n_2}={\left(\frac{d_2}{d_1}\right)}^2=\left(\frac{2}{1}\right)=4\Rightarrow n_2=\frac{n_1}{4}$