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MHT CET 2025 (19 Apr, Shift 1) · Hydrogen Spectrum & Spectral Series

Hydrogen Spectrum & Spectral Series question from MHT CET 2025 (19 Apr, Shift 1)

Q14MHT CET 2025 · 19 APR · SHIFT 1Medium

Hydrogen Spectrum & Spectral Series

If ' λ1\lambda_1 ' and ' λ2\lambda_2 ' are the wavelengths of the first member of the Balmer and Paschen series, in hydrogen atom respectively, then the ratio of respective frequencies, f1/f2f_1/f_2, is

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Answer: (a)

  1. f∝1λ=R(1n12−1n22)f \propto \frac{1}{\lambda} = R\left(\frac{1}{n_1^2} - \frac{1}{n_2^2}\right).
  2. Balmer first line: f1∝14−19=536f_1 \propto \frac{1}{4} - \frac{1}{9} = \frac{5}{36}.
  3. Paschen first line: f2∝19−116=7144f_2 \propto \frac{1}{9} - \frac{1}{16} = \frac{7}{144}.
  4. f1f2=536×1447=207\frac{f_1}{f_2} = \frac{5}{36} \times \frac{144}{7} = \frac{20}{7}.
  5. So the answer is (a) 20:720 : 7.
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