Question: Q. 11. State two important properties of photon which are used to write Einstein’s photoelectric equation. Define (i) stopping potential and (ii) threshold frequency, using Einstein equation and drawing necessary plot between relevant quantities.
R [OD North 2016]
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Solution:
Ans. Properties of Photon :
(i) For a radiation of frequency $v$, each photon has an energy, $E=h v$, associated with it
(ii) The energy of a photon is independent of the intensity of incident radiation.
(iii) During the collision of a photon, with an electron, the total energy of the photon gets absorbed by the electron.
(Any two) $1 / 2+1 / 2$
Einstein’s photoelectric equation is
$$ K_{\max }=h v-\phi_{0} $$
$$ \text { or } \quad e V_{0}=h v-\phi_{0} $$
(i) Stopping potential, $V_{0}$, equals that value of the negative potential for which
$$ \left|e V_{0}\right|=K_{\max } $$
(Alternatively :
The stopping potential $\left(V_{0}\right)$ equals that (least) value of the (negative) plate potential that just stops the most energetic emitted photoelectrons. from reaching the plate.)
(ii) Threshold frequency $\left(v_{0}\right)$ equals that value of the frequency of incident radiation for which
(Alternatively :
$$ K_{\max }=0 $$
For a given photosensitive surface, its threshold frequency is the minimum value of the frequency of incident radiation for which photoelectrons can be just emitted from that surface or that maximum frequency of incident radiation below which no photoemission takes place.)
The plot, between $V_{0}$ and $v$ has the form shown :
[CBSE Marking Scheme 2016]
