CBSE 2025 · Region 4 · Set 2 · Q20 · 2 marks
Find the ratio of minimum to maximum wavelength of radiations emitted when electron jumps from higher energy state into ground state of hydrogen atom.
Marking-scheme solution
$\displaystyle \frac{1}{\lambda}=R\left[\frac{1}{n_{f}^{2}}-\frac{1}{n_{i}^{2}}\right]$
$\displaystyle \frac{1}{\lambda_{\max }}=R\left[\frac{1}{1^{2}}-\frac{1}{2^{2}}\right]$
$\displaystyle \lambda_{\max }=\frac{4}{3 R}$
$\displaystyle \frac{1}{\lambda_{\min }}=R\left[\frac{1}{1^{2}}-\frac{1}{\infty}\right]$
$\displaystyle \lambda_{\min }=\frac{1}{R}$
$\displaystyle \frac{\lambda_{\min }}{\lambda_{\max }}=\frac{3}{4}$
OR
For $\displaystyle \lambda_{\min }$: $\displaystyle n_{1}=1, n_{2}=\infty$
$\displaystyle E_{2}-E_{1}=\frac{h c}{\lambda_{\min }}$
$\displaystyle 0-(-13.6)=\frac{h c}{\lambda_{\min }}$
$\displaystyle \lambda_{\min }=\frac{h c}{13.6}$
For $\displaystyle \lambda_{\max }$: $\displaystyle n_{1}=1, n_{2}=2$
$\displaystyle \lambda_{\max }=\frac{h c}{-3.4-(-13.6)}$
$\displaystyle \lambda_{\max }=\frac{h c}{10.2}$
$\displaystyle \frac{\lambda_{\min }}{\lambda_{\max }}=\frac{3}{4}$AtomsThe Line Spectra of the Hydrogen AtomApplyvery_short_answermedium
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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.