Assertion (A) : In Bohr model of hydrogen atom, the energy levels are discrete and quantised.
Reason (R) : In a hydrogen atom, the electrostatic force on the electron provides the necessary centripetal force to it to revolve around the nucleus.
CBSE CLASS 12 • PHYSICS • CHAPTER 12
Atoms
38 distinct questions across 54 board paper set appearances (2022–2026).
Paschen series in spectrum of hydrogen atom lies in :
(A) infrared region
(B) ultraviolet region
(C) visible region
(D) partly in ultraviolet region and partly in visible region
Assertion (A) : The Balmer series in hydrogen atom spectrum is formed when the electron jumps from higher energy state to the ground state.
Reason (R) : In Bohr's model of hydrogen atom, the electron can jump between successive orbits only.
The transition of electron that gives rise to the formation of the second spectral line of the Balmer series in the spectrum of hydrogen atom corresponds to :
(A) $n_f = 2$ and $n_i = 3$
(B) $n_f = 3$ and $n_i = 4$
(C) $n_f = 2$ and $n_i = 4$
(D) $n_f = 2$ and $n_i = \infty$
Atomic spectral emission lines of hydrogen atom are incident on a zinc surface. The lines which can emit photoelectrons from the surface are members of (A) Balmer series (B) Paschen series (C) Lyman series (D) Neither Balmer, nor Paschen nor Lyman series
In Balmer series of hydrogen atom, as the wavelength of spectral lines decreases, they appear
(A) equally spaced and equally intense.
(B) further apart and stronger in intensity.
(C) closer together and stronger in intensity.
(D) closer together and weaker in intensity.
(a) (i) An electron in a hydrogen atom jumps from second excited state to the first excited state. Name the spectral series in the spectrum of hydrogen atom to which the emitted radiation belongs.
(ii) Find the ratio of the wavelengths of the "most energetic spectral" lines in the Balmer series to t...
Energy levels A, B and C of an atom correspond to increasing values of energy i.e. $E_A < E_B < E_C$. Let $\lambda_1$, $\lambda_2$ and $\lambda_3$ be the wavelengths of radiation corresponding to the transitions C to B, B to A and C to A, respectively. The correct relation between $\lambda_1$, $\lam...
(a) How did de Broglie hypothesis provide an explanation for Bohr's second postulate for quantisation of orbital angular momentum of the orbiting electron in hydrogen atom? Discuss. (b) Identify the transition of electron in Bohr model which gives rise to (i) the maximum, and (ii) the minimum wavele...
(a) State Bohr's second postulate and mention its significance.
(b) Prove that, in Bohr model of hydrogen atom as principal quantum number $n$ becomes large, the energy levels get closer and closer.
(iv) When we dope Ge with a pentavalent element, four of its electrons bond with four germanium neighbours but fifth electron remains weakly bound. The ionisation energy for this electron is about
(A) $0.01\text{ eV}$
(B) $0.05\text{ eV}$
(C) $0.1\text{ eV}$
(D) $0.15\text{ eV}$
OR
(iv) When we dope Ge with a pentavalent element, four of its electrons bond with four germanium neighbours but fifth electron remains weakly bound. The ionisation energy for this electron is about
(A) $0.01\text{ eV}$
(B) $0.05\text{ eV}$
(C) $0.1\text{ eV}$
(D) $0.15\text{ eV}$
In alpha-particle scattering experiment, the impact parameter is minimum when the scattering angle is close to :
(A) $45^{\circ}$
(B) $90^{\circ}$
(C) $135^{\circ}$
(D) $180^{\circ}$
In Bohr's model of hydrogen atom, the angular momentum of electron in second orbit is equal to :
(A) $\frac{\text{h}}{2\pi}$
(B) $\frac{\text{h}}{\pi}$
(C) $\frac{2\text{h}}{\pi}$
(D) $\frac{\text{h}}{4\pi}$
Suppose there is an atom that contains five energy levels. How many transitions are possible in which photons are emitted ? (A) 4 (B) 5 (C) 10 (D) 15
In Bohr's model of hydrogen atom, the potential energy of the electron in the ground state is – (A) $-27.2 \text{ eV}$ (B) $27.2 \text{ eV}$ (C) $-13.6 \text{ eV}$ (D) $13.6 \text{ eV}$
The Balmer series of hydrogen atom lies in :
(A) UV region
(B) Infrared region
(C) Visible region
(D) Microwave region
(iv) (a) In Bohr's model of hydrogen atom, the frequency of revolution of electron in its $ ext{n}^{ ext{th}}$ orbit is proportional to :
(A) n
(B) $\frac{1}{\text{n}}$
(C) $\frac{1}{\text{n}^2}$
(D) $\frac{1}{\text{n}^3}$
OR
(b) An electron makes a transition from $-3\cdot4\text{ eV}$ state to the ...
In Bohr's model of hydrogen atom, the frequency of revolution of electron in its $\text{n}^{\text{th}}$ orbit is proportional to :
(A) $\text{n}$
(B) $\frac{1}{\text{n}}$
(C) $\frac{1}{\text{n}^2}$
(D) $\frac{1}{\text{n}^3}$
OR
An electron makes a transition from $-3\cdot4\text{ eV}$ state to the ground state in hydrogen atom. Its radius of orbit changes by : (radius of orbit of electron in ground state $= 0\cdot53\text{ \AA}$)
(A) $0\cdot53\text{ \AA}$
(B) $1\cdot06\text{ \AA}$
(C) $1\cdot59\text{ \AA}$
(D) $2\cdo...
In Bohr's model of hydrogen atom, find the percentage change in the radius of its orbit when an electron makes a transition from $n = 3$ state to $n = 2$ state.
(iv) (a) In Bohr's model of hydrogen atom, the frequency of revolution of electron in its $n^{\text{th}}$ orbit is proportional to :
(A) $n$
(B) $\frac{1}{n}$
(C) $\frac{1}{n^2}$
(D) $\frac{1}{n^3}$
OR
(b) An electron makes a transition from $-3\cdot4\text{ eV}$ state to the ground state in hydrogen atom. Its radius of orbit changes by : (radius of orbit of electron in ground state $= 0\cdot53\text{ \AA}$)
(A) $0\cdot53\text{ \AA}$
(B) $1\cdot06\text{ \AA}$
(C) $1\cdot59\text{ \AA}$
(D) $2\cdo...
An electron in Bohr model of hydrogen atom makes a transition from energy level -1.51 eV to -3.40 eV. Calculate the change in the radius of its orbit. The radius of orbit of electron in its ground state is 0.53 Å.
Energy levels A, B and C of an atom correspond to increasing values of energy i.e. $E_{\text{A}} < E_{\text{B}} < E_{\text{C}}$. Let $\lambda_1, \lambda_2$ and $\lambda_3$ be the wavelengths of radiation corresponding to the transitions C to B, B to A and C to A, respectively. The correct relation b...
What are the postulates of Bohr's theory of hydrogen atom? Write the expression of radius of $n^{th}$ orbit of electron.
(iii) The second member of Lyman spectral series in absorption hydrogen spectrum results due to electron transition :
(A) $n = 3$ to $n = 1$
(B) $n = 1$ to $n = 3$
(C) $n = 1$ to $n = 2$
(D) $n = 2$ to $n = 1$
The spacing between successive energy levels of hydrogen atom :
(A) is same for all levels
(B) becomes larger for higher levels
(C) becomes smaller for higher levels
(D) may be larger or smaller for higher levels depending upon temperature
An electron makes a transition from orbit $n = 2$ to orbit $n = 1$, in Bohr's model of hydrogen atom. Consider change in magnitudes of its kinetic energy (K) and potential energy (U).
(A) K increases and U decreases
(B) K decreases and U increases
(C) Both K and U decrease
(D) Both K and U increase
The ionisation energy of the hydrogen atom, in Bohr model, is :
(A) $-3.4 \ \text{eV}$
(B) $3.4 \ \text{eV}$
(C) $-13.6 \ \text{eV}$
(D) $13.6 \ \text{eV}$
(a) Two energy levels of an electron in hydrogen atom are separated by 2.55 eV. Find the wavelength of radiation emitted when the electron makes transition from the higher energy level to the lower energy level. (b) In which series of hydrogen spectrum this line shall fall?
The earth revolves around the sun in an orbit of radius 1.5 $\times$ 10$^{11}$ m with orbital speed 30 km/s. Find the quantum number that characterises its revolution using Bohr's model in this case (mass of earth = 6.0 $\times$ 10$^{24}$ kg).
Explain the origin of Lyman and Balmer series in the emission spectrum of hydrogen atom. How are the maximum and the minimum wavelength of lines in a series determined ?
Which of the following series in hydrogen spectrum lies in its visible region ?
(a) Lyman series
(b) Balmer series
(c) Paschen series
(d) Pfund series
(a) Sketch the energy level diagram for hydrogen atom.
(b) Find the ratio of the longest and the shortest wavelength in Lyman series in hydrogen atom.
The energy of a hydrogen atom in the first excited state is $-3.4$ eV. Find :
(a) the radius of this orbit. (Take Bohr radius = $0.53$ Å)
(b) the angular momentum of the electron in the orbit.
(c) the kinetic and potential energy of the electron in the orbit.
What is the nuclear radius of $^{125}\text{Fe}$ ,if that of $^{27}\text{Al}$ is 3.6 fermi?.
OR
The short wavelength limit for the Lyman series of the hydrogen spectrum is 913.4 $\text{A}^0$. Calculate the short wavelength limit for the Balmer series of the hydrogen spectrum.
An electron in a hydrogen atom makes transitions from orbits of higher energies to orbits of lower energies. (i) When will such transitions result in (a) Lyman (b) Balmer series ? (ii) Find the ratio of the longest wavelength in Lyman series to the shortest wavelength in Balmer series.