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MHT CET 2025 (26 Apr, Shift 1) · Hydrogen Spectrum & Spectral Series

Hydrogen Spectrum & Spectral Series question from MHT CET 2025 (26 Apr, Shift 1)

Q13MHT CET 2025 · 26 APR · SHIFT 1Medium

Hydrogen Spectrum & Spectral Series

In Paschen series, wavelength of first line is ' λ1\lambda_1 ' and for Brackett series, wavelength of first line is ' λ2\lambda_2 ' then ratio λ1λ2\frac{\lambda_1}{\lambda_2} is

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Answer: (c)

  1. Paschen first line (4→34 \to 3): 1λ1=R(19−116)=7R144\frac{1}{\lambda_1} = R\left(\frac{1}{9} - \frac{1}{16}\right) = \frac{7R}{144}.
  2. Brackett first line (5→45 \to 4): 1λ2=R(116−125)=9R400\frac{1}{\lambda_2} = R\left(\frac{1}{16} - \frac{1}{25}\right) = \frac{9R}{400}.
  3. λ1λ2=1447×9400=12962800=81175\frac{\lambda_1}{\lambda_2} = \frac{144}{7} \times \frac{9}{400} = \frac{1296}{2800} = \frac{81}{175}.
  4. So the answer is (c) 81175\frac{81}{175}.
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