Question:medium

If '\(\lambda_1\)' and '\(\lambda_2\)' are the wavelengths of the first member of the Balmer and Paschen series, in hydrogen atom respectively, then the ratio of respective frequencies, \(f_1/f_2\) , is

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Find the wavelength of the first line of each series using the Rydberg formula; frequency is inversely proportional to wavelength.
Updated On: Nov 13, 2026
  • \(20 : 7\)
  • \(27 : 5\)
  • \(50 : 9\)
  • \(108 : 7\)
Show Solution

The Correct Option is A

Solution and Explanation

Step 1: Use energy
Photon energy is proportional to $\frac1{n_1^2}-\frac1{n_2^2}$, and the frequency is proportional to the energy.

Step 2: Values
Balmer: $\frac14-\frac19=\frac5{36}$. Paschen: $\frac19-\frac1{16}=\frac7{144}$.

Step 3: Divide
$\frac{5}{36}\div\frac{7}{144}=\frac{20}{7}$, the first option.

Final Answer:
The frequency ratio is $20:7$. \[ \boxed{\text{(A) }20:7} \]
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