We are introduced to the Bohr model of atom one time or the other in the course of physics. This model has its place in the history of quantum mechanics and particularly in explaining the structure of an atom. It has become a milestone since Bohr introduced the revolutionary idea of definite energy orbits for the electrons, contrary to the classical picture requiring an accelerating particle to radiate. Bohr also introduced the idea of quantisation of angular momentum of electrons moving in definite orbits. Thus, it was a semi-classical picture of the structure of atom.
Now with the development of quantum mechanics, we have a better understanding of the structure of atom. Solutions of the Schrodinger wave equation assign a wave-like description to the electrons bound in an atom due to attractive forces of the protons.
An orbit of the electron in the Bohr model is the circular path of motion of an electron around the nucleus.
- Bohr model is valid only for one-electron atom/ions; an energy value, assigned to each orbit, depends on the principal quantum number \( n \) in this model. We know that energy associated with a stationary state of an electron depends on \( n \) only. For one-electron atoms/ions. For a multi-electron atom/ion, this is not true.
In the Hydrogen Spectrum provided by Bohr's model, spectral series falls in ultra-violet region of E.M. wave is:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Lyman series
The region of a spectral series is set by the lower level of the transition. The photon energy is
\( \displaystyle h\nu = 13.6\left(\frac{1}{n_{f}^{2}} - \frac{1}{n_{i}^{2}}\right)\,\mathrm{eV} \)
Transitions that end on \( n_f = 1 \) release the largest energies, from 10.2 eV to 13.6 eV, that is, wavelengths of about 91 nm to 122 nm, which lie in the ultraviolet. This is the Lyman series.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic was removed from the latest NCERT book (2026-27), but it is still in the CUET 2026 syllabus, so do not skip it.
NCERT (Pre-rationalised edition, 2022-23):
Spectral Series – “… The Lyman series is in the ultraviolet, and the Paschen and Brackett series are in the infrared region.”