CBSE 2025 · Region 1 · Set 2 · Q26 · 3 marks
(a)Draw a plot of frequency $\displaystyle v$ of incident radiations as a function of stopping potential $\displaystyle \mathrm{V}_{0}$ for a given photo emissive material. What information can be obtained from the value of the intercept on the stopping potential axis?(b)Calculate: (i) the momentum and (ii) de Broglie wavelength, of an electron with kinetic energy of $\displaystyle 80$ eV.
(a)
Draw a plot of frequency $\displaystyle v$ of incident radiations as a function of stopping potential $\displaystyle \mathrm{V}_{0}$ for a given photo emissive material. What information can be obtained from the value of the intercept on the stopping potential axis?
(b)
Calculate: (i) the momentum and (ii) de Broglie wavelength, of an electron with kinetic energy of $\displaystyle 80$ eV.
Marking-scheme solution
(a)
Value of work function can be obtained from the intercept.
(i)
$\displaystyle p=\sqrt{2 m K}$
$\displaystyle =\sqrt{2 \times 9.1 \times 10^{-31} \times 80 \times 1.6 \times 10^{-19}}$
$\displaystyle =4.8 \times 10^{-24} \mathrm{~kg} \mathrm{~m} / \mathrm{s}$
(ii)
$\displaystyle \lambda=\frac{h}{p}=\frac{6.63 \times 10^{-34}}{4.8 \times 10^{-24}}=1.38 \times 10^{-10} \mathrm{~m}$
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CBSE Class 12 Physics past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.