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Physics · 2023 · 3 marks
CBSE 2023 · Region 2 · Set 1 · Q30
(a) (i) Distinguish between nuclear fission and fusion giving an example of each. (ii) Explain the release of energy in nuclear fission and fusion on…
(a)(i)
Distinguish between nuclear fission and fusion giving an example of each.
(ii)
Explain the release of energy in nuclear fission and fusion on the basis of binding energy per nucleon curve.
OR
(b)(i)
How is the size of a nucleus found experimentally ? Write the relation between the radius and mass number of a nucleus.
(ii)
Prove that the density of a nucleus is independent of its mass number.
Marking-scheme solution
Nuclear fission - It is a process in which a heavy nucleus when excited (say on bombarding by a slow moving neutron) splits into two lighter nuclei of nearly comparable masses with a release of large amount of energy.
Example of nuclear fission
\[{ }_{0}^{1} n+{ }_{92}^{235} \mathrm{U} \rightarrow{ }_{92}^{236} \mathrm{U} \rightarrow{ }_{56}^{144} \mathrm{Ba}+{ }_{36}^{89} \mathrm{Kr}+3{ }_{0}^{1} n+\mathrm{Q}
\]
Nuclear Fusion - It is a process in which two lighter nuclei fuse (at extremely high temperature) to form a heavy nucleus and large amount of energy is released.
Examples of nuclear fusion
(i) \(\displaystyle { }_{1}^{1} \mathrm{H}+{ }_{1}^{1} \mathrm{H} \rightarrow{ }_{1}^{2} \mathrm{H}+e^{+}+v+\mathrm{Q}_{1}\)
(ii) \(\displaystyle { }_{1}^{2} \mathrm{H}+{ }_{1}^{2} \mathrm{H} \rightarrow{ }_{2}^{3} \mathrm{H}+n+\mathrm{Q}_{2}\)
(iii) \(\displaystyle { }_{1}^{2} \mathrm{H}+{ }_{1}^{2} \mathrm{H} \rightarrow{ }_{1}^{3} \mathrm{H}+{ }_{1}^{1} \mathrm{H}+\mathrm{Q}_{3}\)
(ii)
The binding energy per nucleon of the products in the nuclear reactions ( nuclear fission and nuclear fusion) is greater than that of the reactants .
(i) Size of nucleus of an atom is determined by scattering experiments in which fast electrons are used to bombard targets.
Relation between radius and mass number of nucleus.
\[R=R_{0} A^{1 / 3}
\]
(ii) Density of nucleus
\[\begin{aligned}
& \rho=\frac{\text { mass }}{\text { volume }} \\
& \rho=\frac{m \times A}{\dfrac{4}{3} \pi R^{3}} \\
& \rho=\frac{m A}{\dfrac{4}{3} \pi\left(R_{0} A^{1 / 3}\right)^{3}} \\
& \rho=\frac{3 m}{4 \pi R_{0}^{3}}
\end{aligned}
\]
Hence, density of nucleus is independent of mass number ( \(\displaystyle A\) ).
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CBSE Class 12 Physics past-paper question from the 2023 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.