Mass-energy Relation

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A lab worksheet asks students to compute the energy equivalent of one atomic mass unit of matter using Einstein's mass-energy relation, expressed in mega-electronvolts.

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Einstein's mass-energy equivalence, quoted in NCERT, states that a mass $m$ carries rest energy $E=mc^2$, meaning mass and energy are interconvertible. One atomic mass unit is $1	ext{ u}=1.66	imes10^{-27}$ kg, and multiplying by $c^2=(3	imes10^8)^2$ gives about $1.49	imes10^{-10}$ J; dividing by the electronvolt conversion $1.6	imes10^{-19}$ J yields roughly $9.315	imes10^8$ eV, or $931.5$ MeV. This conversion factor, 931.5 MeV per u, is used throughout nuclear physics. The value 511 keV is wrong because that is the rest energy of a single electron, not of one mass unit. The value 1.66 MeV is wrong because it confuses the numerical mantissa of the kilogram value with an energy. The value 8.2 MeV is wrong because that is a typical binding energy per nucleon, a different quantity entirely. As stated in NCERT Class 12, Chapter 13 (Nuclei), expressing masses in u lets one read energies directly using this factor. A magnitude check confirms that a tiny mass unit corresponds to a large nuclear-scale energy, hundreds of MeV, as expected from the huge $c^2$ factor.

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