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Physics · 2026 · 2 marks
CBSE 2026 · Region 1 · Set 3 · Q21
Suppose a nucleus with mass number A =240 and (B. E.)/A=7.6 MeV, breaks into two nuclei, each of mass number A =120 with (B. E.)/A=8.5 MeV. Calculate…
Suppose a nucleus with mass number $\displaystyle \mathrm{A}=240$ and $\displaystyle \frac{\mathrm{B} . \mathrm{E} .}{\mathrm{A}}=7.6 \mathrm{MeV}$, breaks into two nuclei, each of mass number $\displaystyle \mathrm{A}=120$ with $\displaystyle \frac{\mathrm{B} . \mathrm{E} .}{\mathrm{A}}=8.5 \mathrm{MeV}$. Calculate the energy released in the process.
Marking-scheme solution
$\displaystyle \mathrm{E}_{\text {bn }}$ for $\displaystyle (\mathrm{A}=240)$ Nucleus $\displaystyle =7.6 \mathrm{MeV}$
$\displaystyle \mathrm{E}_{\mathrm{bn}}$ for two fragments (A=$\displaystyle 120$)
\[=8.5 \mathrm{MeV}
\]
Gain in $\displaystyle \mathrm{E}_{\text {bn }}=8.5-7.6$
\[=0.9 \mathrm{MeV}
\]
Total gain in binding energy $\displaystyle =240 \times 0.9$
\[=216 \mathrm{MeV}
\]
Alternatively:
Binding energy for $\displaystyle (\mathrm{A}=240)$ nucleus is $\displaystyle =240 \times 7.6 \mathrm{MeV}$
Binding energy for fragments is $\displaystyle =2 \times 120 \times 8.5$
\[=240 \times 8.5 \mathrm{MeV}
\]
Energy released $\displaystyle =240 \times 8.5-240 \times 7.6$
\[=240 \times(8.5-7.6)
\]
$\displaystyle =240 \times 0.9$
\[=216 \mathrm{MeV}
\]
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