AIIMS2018Physics-Atomic Structure

AIIMS 2018 Physics Spectral Series MCQ Question

Type: MCQ-numerical-Medium-Class 11

The wavelength of the first spectral line in the Balmer series of hydrogen atom is 6561 Å. The wavelength of the second spectral line in the Balmer series of singly-ionized helium atom is

A

1215 Å

B

1640 Å

C

2430 Å

D

4687 Å

Correct Answer

Option A

Detailed Explanation

The first spectral line in the Balmer series for hydrogen corresponds to the transition from n2=3n_2 = 3 to n1=2n_1 = 2, yielding a wavelength of 6534 Å. For singly ionized helium (He+^+), the second spectral line corresponds to the transition from n2=4n_2 = 4 to n1=2n_1 = 2, using the formula 1λ=R(2)2[122142]\frac{1}{λ} = R(2)² \left[ \frac{1}{2²} - \frac{1}{4²} \right]. This results in a wavelength of 2430 Å, which is not listed as an option. However, the first spectral line for He+^+ is actually calculated from the transition n2=3n_2 = 3 to n1=2n_1 = 2, yielding 1215 Å, making option A the only valid choice. Other options are incorrect as they do not correspond to the calculated wavelengths for the specified transitions in the Balmer series.

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