CBSE 2025 · Region 5 · Set 1 · Q17 · 2 marks
The threshold frequency for a given metal is $\displaystyle 3.6 \times 10^{14} \mathrm{~Hz}$. If monochromatic radiations of frequency $\displaystyle 6.8 \times 10^{14} \mathrm{~Hz}$ are incident on this metal, find the cut-off potential for the photoelectrons.
Marking-scheme solution
$\displaystyle e V_{0}=h\left(\nu-\nu_{0}\right)$
$\displaystyle V_{0}=\frac{6.63 \times 10^{-34} \times(6.8-3.6) \times 10^{14}}{1.6 \times 10^{-19}}$
$\displaystyle =1.33 \mathrm{~V}$
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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.