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Q.
The energy released by the fission of one uranium atom is $200\, MeV$. The number of fission per second required to produce $3.2\, W$ of power is (Take, $1\, e\, V\, = \,1.6 \times$ $10^{-19} \, J)$
We have the energy released by fission of one uranium atom is $200\, MeV$.
So, $E=200 \times 10^{6} \times 1.6 \times 10^{-19}$
$=3.2 \times 10^{-11}\, J$
The power required $=3.2\, W$
Thus the number of fissions required is equal to
$\frac{3.2}{3.2 \times 10^{-11}}=10^{11}$ fissions.