Class 12 Nuclei Mock Test (CBSE)

Topics in Nuclei

• Atomic masses and composition of nucleus
• Size of the nucleus
• Mass-energy relation
• Nuclear binding energy
• Nuclear force
• Nuclear energy
• Nuclear fission
• Nuclear fusion

Nuclei practice questions with answers

1. Q1Multiple choice·1 mark
   Which of the following quantities serves as a direct measure of the stability of a nucleus?

   1. (a)Total binding energy
   2. (b)Mass number
   3. (c)Binding energy per nucleon
   4. (d)Neutron number
   Show answer and step marks

   1. Correct option: (c). Binding energy per nucleon determines how tightly nucleons are bound together, making it a direct measure of nuclear stability.+1

   Answer: (c)
2. Q2Multiple choice·1 mark
   Which of the following characteristics is true for nuclear forces between nucleons?

   1. (a)They are long-range electrostatic forces.
   2. (b)They depend strongly on the electric charge of the nucleons.
   3. (c)They are charge-independent and strongly attractive at short distances.
   4. (d)They obey the inverse-square law.
   Show answer and step marks

   1. Correct option: (c). Nuclear forces are essentially charge-independent and are strongly attractive, acting over very short ranges without following an inverse-square law.+1

   Answer: (c)
3. Q3Multiple choice·1 mark
   The radius of a nucleus with mass number $A$ is given by $R = R_0 A^{1/3}$. If the mass number of a nucleus increases from 8 to 64, the ratio of the nuclear radii of the two nuclei is:

   1. (a)$1:8$
   2. (b)$1:4$
   3. (c)$1:2$
   4. (d)$2:1$
   Show answer and step marks

   1. Correct option: (c) $1:2$. Since $R \propto A^{1/3}$, the ratio is $(8/64)^{1/3} = (1/8)^{1/3} = 1/2$.+1

   Answer: (c)
4. Q4Short answer·2 marks
   Calculate the energy equivalent of $1\text{ u}$ of atomic mass in MeV using the mass-energy relation.
   Show answer and step marks

   1. Use $E = mc^2$ with $m = 1\text{ u} = 1.6605 \times 10^{-27}\text{ kg}$ and $c = 2.9979 \times 10^8\text{ m/s}$: $E = 1.4924 \times 10^{-10}\text{ J}$.+1
   2. Convert to MeV using $1\text{ MeV} = 1.6022 \times 10^{-13}\text{ J}$: $E \approx 931.5\text{ MeV}$ (rounded constants $1.66 \times 10^{-27}$ kg, $3 \times 10^8$ m/s and $1.6 \times 10^{-13}$ J give about $934$ MeV, also accepted).+1

   Answer: $\approx 931.5\text{ MeV}$ (about $934$ MeV with rounded constants)
5. Q5Short answer·3 marks
   Calculate the binding energy per nucleon (in $\text{MeV}$) of a ${}^{16}_{8}\text{O}$ nucleus. Given: atomic mass of ${}^{16}_{8}\text{O} = 15.9949\text{ u}$, mass of a hydrogen atom $m_H = 1.00783\text{ u}$, mass of a neutron $m_n = 1.00867\text{ u}$, and $1\text{ u} = 931.5\text{ MeV}$.
   Show answer and step marks

   1. Identify the number of protons ($Z = 8$) and neutrons ($N = 16 - 8 = 8$) in the oxygen nucleus.+0.5
   2. Calculate the mass defect using atomic masses (electron masses cancel): $\Delta m = [Zm_H + Nm_n] - M = [8(1.00783) + 8(1.00867)] - 15.9949 = 16.13200 - 15.9949 = 0.1371\text{ u}$.+1
   3. Calculate the total binding energy: $BE = 0.1371 \times 931.5 = 127.71\text{ MeV}$.+1
   4. Binding energy per nucleon $= \frac{127.71}{16} = 7.98\text{ MeV/nucleon}$.+0.5

   Answer: $7.98\text{ MeV/nucleon}$

More Class 12 Physics mock tests