Question: Q. 13. Plot agraph showing the variation of photoelectric current with intensity of light. The work function for the following metals is given : $\mathrm{Na}: 2.75$ $\mathrm{eV}$ and Mo : $4.175 \mathrm{eV}$. Which of these will not give photoelectron emission from a radiation of wavelength $3300 \AA$ from a laser beam ? What happens if the source of laser beam is brought closer ?
$\mathrm{R}$ [Foreign I, II, III 2016]
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Solution:
Ans. (i)
(ii) Energy of a photon,
$$ \begin{aligned} E & =\frac{h c}{\lambda} \text { Joule } \ & =\frac{h c}{e \lambda} \mathrm{eV} \ & =\frac{6.63 \times 10^{-34} \times 3 \times 10^{8}}{1.6 \times 10^{-19} \times 3.3 \times 10^{-7}} \mathrm{eV} \ & =3.75 \mathrm{eV} \end{aligned} $$
$1 / 2$
Since $\phi_{0}$ of Mo is greater than $E$,
$\therefore$ Mo will not give photo emission.
$1 / 2$
There will be no effect of bringing source closer in the case of Mo. In case of Na, photo current will increase.
[CBSE Marking Scheme 2016]
Detailed Answer :
(ii) Try yourself similar to Q. 7, SATQ-II
