Question

Sketch a graph between frequency of incident radiations and stopping potential for a given photosensitive material. What information can be obtained from the value of the intercept of potential axis?

A source of light of frequency of greater than the threshold frequency is placed at a distance of 1 m from the cathode of a photocell. The stopping potential is found to be V. If the distance of the light source from the cathode is reduced, explain giving reasons, what change will you observe in the:

(i) Photoelectric current,

(ii) Stopping potential?

Answer 1

For first part:

Graph between stopping potential V₀ and frequency v is as shown in figure.

According to Einstein photoelectric equation

eV = hv - W₀ .............(1)

where W₀ is the work function and is constant for a substance.

Differentiating equation (i) partially, we get

It is given that stopping potential is V and v > v₀.

(i) Photoelectric current will increase as the distance between source from the cathode is decreased.

(ii) Stopping potential will remain the same, till the frequency of incident radiation remains the same.