CBSE 2022 · Region 5 · Set 3 · Q7 · 3 marks
(a)Give an example each of a metal from which photoelectric emission takes place when irradiated by (i) UV light (ii) visible light.(b)The work function of a metal is $\displaystyle 4.50$ eV. Find the frequency of light to be used to eject electrons from the metal surface with a maximum kinetic energy of $\displaystyle 6.06 \times 10^{-19} \mathrm{~J}$.
(a)
Give an example each of a metal from which photoelectric emission takes place when irradiated by (i) UV light (ii) visible light.
(b)
The work function of a metal is $\displaystyle 4.50$ eV. Find the frequency of light to be used to eject electrons from the metal surface with a maximum kinetic energy of $\displaystyle 6.06 \times 10^{-19} \mathrm{~J}$.
Marking-scheme solution
(i) UV light --- Zinc, Magnesium, Cadmium
(ii) Visible light --- Alkali metals like Sodium, Potassium, Lithium
(b)
From Einstein for equation of photo electric effect
$$\mathrm{h} v=\mathrm{W}_{\mathrm{o}}+\mathrm{KE}_{\max }
$$=$\displaystyle 4.5$ \times $\displaystyle 1.6$ \times $\displaystyle 10$^{-$\displaystyle 19$}+$\displaystyle 6.06$ \times $\displaystyle 10$^{-$\displaystyle 19$}
$$=($\displaystyle 7.2$+$\displaystyle 6.06$) \times $\displaystyle 10$^{-$\displaystyle 19$} \mathrm{~J}
$$=$\displaystyle 13.26$ \times $\displaystyle 10$^{-$\displaystyle 19$} \mathrm{~J}
$$\begin{aligned}
v= & \frac{$\displaystyle 13.26$ \times $\displaystyle 10$^{-$\displaystyle 19$}}{$\displaystyle 6.6$ \times $\displaystyle 10$^{-$\displaystyle 34$}}
& =$\displaystyle 2$ \times $\displaystyle 10$^{$\displaystyle 15$} \mathrm{~Hz}
\end{aligned}
Dual Nature of Radiation and MatterEinstein’s Photoelectric Equation: Energy Quantum of RadiationApplyshort_answermedium
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CBSE Class 12 Physics past-paper question from the 2022board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.