Question

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

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

Answer 1

The correct option is B number of electrons emitted is a quarter of the initial number

Intensity of light source is $I\propto \frac{1}{d^2}\therefore \frac{I_2}{I_1}={\left(\frac{d_1}{d_2}\right)}^2={\left(\frac{1}{2}\right)}^2=\frac{1}{4}\Rightarrow I_2=\frac{I_1}{4}.$
Number of electrons emitted depends upon the Intensity, and energy of the electrons emitted is independent of the Intensity