Einstein’s mass - energy relation emerging out of his famous theory of relativity relates mass (m ) to energy (E ) as E = mc2, where c is speed of light in vacuum. At the nuclear level, the magnitudes of energy are very small. The energy at nuclear level is usually measured in MeV, where 1 MeV= 1.6×10-13 J; the masses are measured in unified atomic mass unit (u) where 1u = 1.67 × 10-27 kg.

(a) Show that the energy equivalent of 1 u is 931.5 MeV.

(b) A student writes the relation as 1 u = 931.5 MeV. The teacher points out that the relation is dimensionally incorrect. Write the correct relation.

0 3 Views | Posted 3 months ago
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    Answered by

    Payal Gupta | Contributor-Level 10

    3 months ago

    This is a long answer type question as classified in NCERT Exemplar

    (a) 1 amu = 1.67 × 10-27kg

    And energy E=mc2= (1.67 × 10-27) (3 × 10 8 )2J

    E= 939.4MeV

    (b) So dimensionally correct relation will be E=amu × c2

    = 1uc2

    = 931.5MeV

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