Question

The anode voltage of a photocell is kept fixed. The frequency of the light falling on the cathode is gradually increased. Then the correct graph which shows the variation of photo current \( I \) with the frequency \( f \) of incident light is 

• A.
• B.
• C.
• D.

Hint:

The photoelectric effect shows a sharp increase in current only when the frequency exceeds a certain threshold frequency. Beyond that, the photo current does not increase with further increase in frequency.

Answer 1

The Correct Option is C

As the frequency of light is increased, the photo current initially increases. However, once the frequency of the incident light exceeds a certain threshold frequency (\( f_0 \)), further increase in frequency will not increase the photo current because the energy of the individual photons exceeds the work function, and no further electron emission occurs. Thus, the correct variation of photo current with frequency of light will look like graph (3).
Thus, the correct graph is (3).