Question

Explain the effect of potential difference on photoelectric current.

Answer 1

1. The effect of potential difference on photoelectric current can be studied by keeping the frequency and the intensity of the incident light constant.

Variation of photocurrent with a potential difference

2. If the cathode is irradiated the potential of A is increased thereby increase in the photocurrent.

3. When all the photoelectrons from C are collected by A the photocurrent reaches a maximum called saturation current.

4. When a negative (retarding) potential is applied to A with respect to C the photoelectrons start to decrease because more and more photoelectrons are being repelled away.

5. The photocurrent becomes zero at a particular negative potential V₀ called stopping or cut off potential.

6. The negative potential applied to anode A which is just sufficient to stop the most energetic photoelectrons to make photocurrent zero is called stopping potential.

7. The kinetic energy of the fastest electron (K_max) is equal to the work done by the stopping potential to stop it (eV₀)

K_max = `1/2 "mv"_"max"^2 = "eV"_0` .........(1)

where v_max is the maximum speed of the photo electrons

v_max = `sqrt((2"eV"_0)/"m")`

= `sqrt((2 xx 1.602 xx 10^-19)/(9.1 xx 10^-31) xx "V"_0)`

v_max = `5.93 xx 10^5 sqrt"V"_0` .........(2)

K_max = eV₀ (in Joule) or K_max = V₀ (in eV)

8. The maximum kinetic energy of the photoelectrons is independent of the intensity of the incident light.