Question

Find the energy equivalent of one atomic mass unit.first in Joules and then in MeV. Using this, express the mass defect of ${}_8^{16}O$ in MeV/$c^2$.

Answer 1

$1amu=1.66\times {10}^{27}kg$

$C=$ speed of light $=3\times {10}^{8}m/s$

$E=m{C}^2$

$=1.66\times {10}^{27}{(3\times {10}^8)}^2=1.49\times {10}^{-10}$ Joule

$1meV=1.6\times {10}^{-13}J$

$E=\frac{1.49\times {10}^{-10}}{1.6\times {10}^{-13}}=931.6MeV$

$O_8^{16}=$ mass no. $=16$

energy for $16amu=16\times 931.6=14905.6MeV$

Mass defect$=\frac{energy}{C^2}=\frac{14905.6MeV}{C^2}$