Write and explain the Einstein theory of special relativity. 

From theory of special relativity it is necessary to treat mass as another form of energy.

Before the theory of special relativity it was presumed that mass and energy were conserved separately in a reaction.

But Einstein showed that mass is another form of energy and one can convert mass-energy into other forms of energy like kinetic energy and vice-versa.

This mass energy equivalent is related to $\mathrm{E}=m c^{2}$ where $m=$ mass, $c=$ velocity of light in vacuum. Its value is equal to $3 \times 10^{8} \mathrm{~ms}^{-1}$.

Experimental verification of the Einstein's mass-energy relation has achieved in the study of nuclear reactions among nucleons, nuclei, electrons and other more recently discovered particles. In a reaction the conservation of law of energy states that the initial energy and the final energy are equal.

This concept is important in understanding nuclear masses and the interaction of nuclei with one another.