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Physics · 2025 · 3 marks
CBSE 2025 · Region 1 · Set 1 · Q27
(a) Define'Mass defect'and'Binding energy'of a nucleus. Describe 'Fission process'on the basis of binding energy per nucleon. (b) A deuteron contains…
(a)
Define'Mass defect'and'Binding energy'of a nucleus. Describe 'Fission process'on the basis of binding energy per nucleon.
(b)
A deuteron contains a proton and a neutron and has a mass of $\displaystyle 2.013553$ u. Calculate the mass defect for it in $\displaystyle \mathrm{u}$ and its energy equivalence in MeV. $\displaystyle \left(\mathrm{m}_{\mathrm{p}}=1.007277 \mathrm{u}, \mathrm{m}_{\mathrm{n}}=1.008665 \mathrm{u}, 1 \mathrm{u}=931.5\right.$ $\displaystyle \left.\mathrm{MeV} / \mathrm{c}^{2}\right)$
Marking-scheme solution
(a)
Difference in the mass of the nucleus and its constituents is defined as mass defect. Binding Energy is the energy required to separate the nucleons from the nucleus. In Fission process a heavy nucleus splits into lighter nuclei and energy is released. As a result the Binding Energy per nucleon increases.
(b)
\(\displaystyle \Delta \mathrm{m}=\left(\mathrm{m}_{\mathrm{p}+} \mathrm{m}_{\mathrm{n})}-\mathrm{m}_{\mathrm{d}}\right.\)
\[\Delta \mathrm{m}=(1.007277+1.008665)-2.013553
\]
\[\Delta \mathrm{m}=0.002389 \mathrm{u}
\]
\[\text { Energy released }=\Delta \mathrm{m} \times \mathrm{c}^{2}
\]
\[\text { Energy released }=0.002389 \times 931.5
\]
\[=2.2253 \mathrm{MeV} \approx 2.22 \mathrm{MeV}
\]
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CBSE Class 12 Physics past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.