we have already seen that most of the atom is empty. Ordinary matter consisting of atoms has a large amount of empty space. E XAMPLE . Example .
Given the mass of iron nucleus as .85u and A= , find the nuclear density? Solution m Fe = . u = . × – kg Nuclear density = mass volume = .
( / )( . ) = . × kg m – The density of matter in neutron stars (an astrophysical object) is comparable to this density. This shows that matter in these objects has been compressed to such an extent that they resemble a big nucleus .
. . Mass – Energy Einstein showed from his theory of special relativity that it is necessary to treat mass as another form of energy. Before the advent of this theory of special relativity it was presumed that mass and energy were conserved separately in a reaction.
However, Einstein showed that mass is another form of energy and one can convert mass-energy into other forms of energy, say kinetic energy and vice-versa. Einstein gave the famous mass-energy equivalence relation E = mc ( . ) Here the energy equivalent of mass m is related by the above equation and c is the velocity of light in vacuum and is approximately equal to × m s – . Example .
Calculate the energy equivalent of g of substance. Solution Energy, E = – × ( × ) J E = – × × = × J Thus, if one gram of matter is converted to energy, there is a release of enormous amount of energy. Experimental verification of the Einstein’s mass-energy relation has been achieved in the study of nuclear reactions amongst nucleons, nuclei, electrons and other more recently discovered particles. In a reaction the conservation law of energy states that the initial energy and the final energy are equal provided the energy associated with mass is also included.
This concept is important