The energy equivalent of one unified atomic mass unit (1 u) is closest to
A$1.602\,\text{eV}$
B$1.66\,\text{eV}$
C$931.5\,\text{MeV}$
D$8.0\,\text{MeV}$
Answer & Solution
Correct answer: C. $931.5\,\text{MeV}$
1. Use Einstein's mass-energy relation $E = mc^2$.
2. NCERT Example 13.3 computes: $1\,u = 1.66054\times 10^{-27}\,\text{kg}$, $c = 2.998\times 10^{8}\,\text{m/s}$.
3. $E = (1.66054\times 10^{-27})(2.998\times 10^{8})^2 = 1.4924\times 10^{-10}\,\text{J}$.
4. Convert to MeV: $1\,\text{MeV} = 1.602\times 10^{-13}\,\text{J}$, so $E = \dfrac{1.4924\times 10^{-10}}{1.602\times 10^{-13}} = 931.5\,\text{MeV}$.
5. This number is THE standard conversion used in nuclear physics: $1\,u \leftrightarrow 931.5\,\text{MeV}/c^2$. It appears in every nuclear binding-energy calculation.
6. Option A is just $1\,\text{eV}$ in joules (confusing constants). Option C is the numerical value of $u$ itself (in kg) misread as eV. Option D is the typical BE/nucleon value, not the u-equivalent.
_Source: NCERT Class 12 Physics Part 2, Ch 13, Example 13.3, p. 6._
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