CBSE-CLASS-XII SERIES

Physics

Atomic Physics

10 previous year questions.

Volume: 10 Ques

Yield: Medium

High-Yield Trend

10

2025

Chapter Questions
10 MCQs

01

PYQ 2025

easy

physics ID: cbse-cla

Out of the four options given, in which transition will the emitted photon have the maximum wavelength?

1

to

2

to

3

to

4

to

02

PYQ 2025

medium

physics ID: cbse-cla

Two statements are given, one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C), and (D) as given below. Two statements are given, one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as given below. Assertion (A): The Balmer series in the hydrogen atom spectrum is formed when the electron jumps from a higher energy state to the ground state. Reason (R): In Bohr's model of the hydrogen atom, the electron can jump between successive orbits only.

1

Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).

2

Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).

3

Assertion (A) is true, but Reason (R) is false.

4

Both Assertion (A) and Reason (R) are false.

03

PYQ 2025

easy

physics ID: cbse-cla

Find the ratio of minimum to maximum wavelength of radiations emitted when an electron jumps from higher energy state into ground state of hydrogen atom.

04

PYQ 2025

easy

physics ID: cbse-cla

Assertion (A): The potential energy of an electron revolving in any stationary orbit in a hydrogen atom is positive. Reason (R): The total energy of a charged particle is always positive.

1

Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

2

Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).

3

Assertion (A) is true, but Reason (R) is false.

4

Assertion (A) is false and Reason (R) is also false.

05

PYQ 2025

easy

physics ID: cbse-cla

An electron in Bohr model of hydrogen atom makes a transition from energy level to . Calculate the change in the radius of its orbit. The radius of orbit of electron in its ground state is .

06

PYQ 2025

easy

physics ID: cbse-cla

How is the necessary force provided to an electron to keep it moving in a circular orbit according to Bohr model of hydrogen atom? Derive an expression for the total energy of an electron moving in an orbit of radius in hydrogen atom. Give the significance of the negative sign in this expression.

Official Solution

Correct Option: (1)

In Bohr’s model of the hydrogen atom, the electron moves in a circular orbit around the nucleus under the influence of the electrostatic (Coulomb) force. The necessary centripetal force to keep the electron in its orbit is provided by the electrostatic force between the electron and the proton in the nucleus. (i) Necessary force to keep the electron moving in a circular orbit: According to Coulomb’s law, the electrostatic force between the electron and the proton is given by: where: - is the charge of the electron (), - is the radius of the orbit, - is the permittivity of free space. For an electron to move in a circular orbit, the centripetal force required is: where: - is the mass of the electron, - is the velocity of the electron. According to Bohr’s postulate, the centripetal force is provided by the electrostatic force, so: (ii) Derivation of the total energy of the electron: To find the total energy of the electron, we need to calculate both the kinetic energy and the potential energy of the electron. 1. Kinetic Energy: The kinetic energy of the electron is given by: From the centripetal force equation: Thus: 2. Potential Energy: The potential energy between two charges (electron and proton) is given by: The negative sign indicates that the electron is bound to the nucleus (attractive force). 3. Total Energy: The total energy of the electron is the sum of its kinetic and potential energies: Substituting the expressions for and : Thus, the total energy of the electron is: Significance of the negative sign: The negative sign in the expression for total energy indicates that the electron is bound to the nucleus by the electrostatic force. If the total energy were positive, it would mean that the electron is not bound to the nucleus and would escape (ionization). Therefore, the negative sign reflects the fact that the electron is in a bound state, and work is required to remove the electron from the atom.

07

PYQ 2025

medium

physics ID: cbse-cla

How is Coulomb repulsion between protons in a nucleus overcome? Explain.

08

PYQ 2025

medium

physics ID: cbse-cla

Why is the mass of a nucleus always less than the sum of the masses of its constituents, i.e. free neutrons and free protons?

09

PYQ 2025

medium

physics ID: cbse-cla

In Bohr model of hydrogen atom, an electron is revolving in second orbit. Find the value of: (i) angular momentum of electron, (ii) radius of the orbit, and (iii) kinetic energy of electron. Take radius of first orbit of hydrogen atom as 0.5 \AA.

10

PYQ 2025

medium

physics ID: cbse-cla

Write the mathematical forms of three postulates of Bohr’s theory of the hydrogen atom. Using them, prove that for an electron revolving in the orbit: (a) the radius of the orbit is proportional to, and (b) the total energy of the atom is proportional to .