Question

In terms of energy $1$ amu is equal to:

• A. 100 J
• B. 931.1 kcal
• C. 931.1 MeV
• D. $10^{7}erg $

Answer 1

Answer: (C)

$1\, amu =1.67 \times 10^{-24} g$
Energy equivalent to this mass can be calculated by using the relation;
$E =m c^{2}$
Here $m =1.67 \times 10^{-24} g$
$c=3 \times 10^{10} cm\, \sec ^{-1}$
$\therefore E =1.67 \times 10^{-24} \times\left(3 \times 10^{10}\right)^{2}$ ergs
$=\frac{1.503 \times 10^{-3}}{10^{7}} J$
$=1.503 \times 10^{-10} J$
Now, $1.6 \times 10^{-19} J =1\, eV$
$1\, J =\frac{1}{1.6 \times 10^{-19}} eV$
$=6.25 \times 10^{18} eV$
$\therefore 1.503 \times 10^{-10} J$
$=6.25 \times 10^{18} \times 1.503 \times 10^{-10} eV$
$=9.393 \times 10^{8} eV$
$\therefore 1\, amu =939.3\, MeV$