2001 AIPMT Dual Nature of Radiation and MatterEffect of Intensity on Photoelectric Current Easy Question 80 of 82 in 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 : -

A Remain same
B Four times
C Two times
D One-fourth

The answer is B.

Solution

For a point source, intensity $I \propto \dfrac{1}{d^2}$.
When the distance is halved, the intensity becomes $\dfrac{1}{(1/2)^2} = 4$ times.
The number of photoelectrons emitted per second is proportional to the intensity (number of photons per second).
So the number of electrons emitted per second becomes four times.

Concept Inverse square law and photocurrent

Dual Nature of Radiation and Matter in past papers

82 questions from this chapter have appeared across 27 exam years.