Question

Define the term threshold frequency and stopping potential in relation to phenomenon of photoelectric effect. How is the photoelectric current affected on increasing the 

(i) frequency

(ii) intensity of incident radiation and why?

Answer 1

Threshold frequency: The minimum value of frequency of incident radiation below which photoelectric emission stops altogether is called Threshold frequency.

Stopping potential: The value of retarding potential at which the photoelectric current becomes zero is called stopping potential for the given frequency of incident radiations.

• When the frequency of incident radiation is increased (at constant intensity of radiation), the photoelectric current remains constant.
• When intensity of incident radiation is increased, there is an increase in number of photons falling on the surface of photosensitive material and hence photoelectric current increases with intensity of radiation.