Dual Nature of Radiation and Matter

A photo-cell is illuminated by a source of light, which is placed at a distance d from the cell. If the distance becomes d/2, then number of electrons emitted per second, will be

1. remain same
2. four times
3. two times
4. one-fourth

Answer

(2) four times

Solution

Number of photoelectrons emitted per second ∝ intensity of incident light.

For a point source, I 1d2

⇒ I'I = ( dd/2 )2 = 4

∴ The number of electrons emitted per second becomes four times.

Answer: (2)