Question: Q. 1. Write Einstein’s photoelectric equation. Explain the terms (i) threshold frequency and (ii) stopping potential.
R [Delhi Comptt. I, II, III 2013; OD I, II, III, 2012]
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Solution:
Ans. (i) Einstein’s photoelectric equation,
K.E. of photoelectron = Incident energy of photons
- Work function
$$ \begin{array}{ll} \text { or, } & \text { K.E. }=h v-\phi_{0} \ \text { or, } & \text { K.E. }=h v-h v_{0} \end{array} $$
where, $v_{0}$ is called threshold frequency.
Threshold Frequency : For a given metal, ther exists a certain minimum frequency of the incident radiation below which no emission of photoelectrons takes place. This frequengy is cafled threshold frequency. It is denoted by 1
(ii) Stopping Potential : It is that minimum negative potential given to anode in a photocell for which the photoelectric current becomesero. It is denoted by $V_{0}$. It is independent of the intensity of the incident light.
Commonly Made Errors
- A few students answered incorrectly as they did not know Einstein’s photoelectric equation.
- Some students gave answer $h v=h v_{0}+k_{\text {max }}$ or $\mathrm{W}+k_{\text {max }}$ or other wrong statements.
