Nuclear Energy : o
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The energy released from the nuclear reactions , either fission or fusion , is called as nuclear energy .
Nuclear fusion and fission are manifestations of the equivalence of mass and energy .
In fusion light atom nuclei like Hydogen fuse to form a bigger nucleus whose mass is less than the sum of the masses of the reactants .
In fission , a heavy nucleus like uranium 235 U92 , is split by a neutron into lighter nuclei . Once again the final mass is less than the initial mass and the mass difference translates into energy .
The Equivalence of Mass and Energy
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Physicists believed that in every physical and chemical process , the mass of an isolated system is conserved till Albert Einstein show the relation , E = m c 2 where c , the speed of light in vacuum is approximately 3 × 10 8 m s – 1 . This equation showed that mass and energy are equivalent and are related by E = m c 2 .
If there is a difference between the sum of reactants and products that differene , Dm , is called mass defect .
In case of chemical reactions the mass defect is very small and can be neglected , but in the case of nuclear reactions this becomes significant .
Principle of Conservation of Energy o
If the forces involved are non-conservative , part of the mechanical energy may get transformed into other forms such as heat , light and sound .
o However , the total energy of an isolated system does not change .
o Since the universe as a whole may be viewed as an isolated system , the total energy of the universe is constant .