# Class 12 Physics MCQ – Nuclear Force

This set of Class 12 Physics Chapter 13 Multiple Choice Questions & Answers (MCQs) focuses on “Nuclear Force”.

1. Which of the following best define nuclear forces?
a) The attraction between protons and neutrons
b) Repulsion between protons and neutrons
c) The attraction between protons and electrons
d) The attraction between electrons and neutrons

Explanation: The protons and neutrons are held together by the strong attractive forces inside the nucleus of an atom. These forces are known as nuclear forces. The other statements are not valid and do not define nuclear forces.

2. Find the true statement.
a) Nuclear charge is dependent on the charge
b) The nuclear force is weaker than the electromagnetic force
c) The nuclear force is independent of charge
d) The nuclear force is weaker than the gravitational force

Explanation: Nuclear force is independent of charge. The nuclear force between two protons is the same as that between two neutrons or between a neutron and proton. This is known as charge independent character of nuclear force. Also, nuclear force is stronger than the electromagnetic and gravitational force.

3. What is the energy released in a nuclear reaction called?
a) R-value
b) Q value
c) P-value
d) Nuclear energy

Explanation: In a nuclear reaction, the sum of masses before the reaction is greater than the sum of masses after the reaction. The difference in masses appears in the form of energy following the law of inter-conversion of mass and energy. Thus, the energy released in a nuclear reaction is called a Q value of a reaction.

4. The nuclear force is short-ranged.
a) True
b) False

Explanation: Yes, this is a true statement. The nuclear force exists in small regions, i.e. the diameter of 10-15 m = 1 fm. The nuclear force between two nucleons decreases rapidly as the separation between them increases and becomes negligible at separation more than 10 fm.

5. Which of the following is the main result of nuclear fission?
a) Helium
b) Strontium
c) Krypton
d) Barium

Explanation: The breaking of a heavy nucleus into two or more fragments of comparable masses, with the release of a tremendous amount of energy is called nuclear fission. The most typical fission reaction occurs when slow-moving neutrons strike Uranium 235 to form the main product barium. The nuclear reaction is given as:
$$_{92}^{235}$$U + $$_0^1$$n ➔ $$_{56}^{141}$$Ba + $$_{36}^{92}$$Kr + 3$$_{0}^{1}$$n + 200 MeV

6. Uranium 235 mass should be greater than X, then it is capable of continuous fission by itself. Identify X.
a) Critical size
b) Threshold point
c) Critical shape
d) Specific size

Explanation: If more than one of the neutrons produced in the fission of uranium 235 is capable of inducing a fission reaction, then the number of fissions taking place at successive stages goes increasing at a very brisk rate and this generates a series of fission reactions. This is known as a chain reaction. If the mass of the Uranium235 sample is greater than a certain size called the critical size then it is capable of continuous fission by itself. So, X is critical size.

7. Which of the following forms the basis of a nuclear reactor?
a) Uncontrolled chain reaction
b) Fast nuclear reaction
c) Controlled chain reaction
d) Catalyst controlled nuclear reaction

Explanation: In a chain reaction, the fast-moving neutrons are absorbed by certain substances known as moderators such as heavy water, then the number of fissions can be controlled and the chain reaction in such a case is known as a controlled chain reaction. This forms the basis of a nuclear reactor.

8. Controlled chain reactions form the basis of an atomic bomb.
a) True
b) False

Explanation: No, this is a false statement. Uncontrolled chain reactions form the basis of an atomic bomb. If the number of fissions in a given interval of time goes on increasing continuously, then a condition of an explosion is created, and this is known as uncontrolled chain reactions.

9. Why is a fusion reaction difficult to perform?
a) The nuclei are set up far from each other
b) The attraction between the nuclei
c) Sun’s energy is not sufficient
d) Repulsion between the nuclei

Explanation: For the fusion reaction to occur, the light nuclei are brought closer to each other, at a distance of about 10-14 m. This is only possible at a very high temperature to counter the repulsive force between the two nuclei. Due to this reason, the fusion reaction is difficult to perform.

10. What is the energy released in the fission of 2 kg of Uranium 235? (Given: energy per fission = 200 MeV)
a) 1.64 × 1014 J
b) 1.64 × 1015 J
c) 2.64 × 1014 J
d) 1.64 × 1020 J

Explanation: Given: energy per fission = 200 MeV; For Uranium 235:
The number of atoms in 235 g = 6.023 × 1023
So, the number of atoms in 2 kg of Uranium 235 = $$( \frac {2000}{235} )$$ × 6.023 × 1023
N = 5.125 × 1024
Therefore, the energy released in fission of 2 kg of Uranium 235 is:
E = 200 MeV × N × 1.6 × 10-19 J
E = 200 × 106 × 5.125 × 1024 × 1.6 × 10-19 J
E = 1.64 × 1014 J

Sanfoundry Global Education & Learning Series – Physics – Class 12.

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