Physics · nuclei · NEET
In a nuclear reaction a small part of the mass is converted into energy, not the whole thing. The total mass-energy is still conserved. Before Einstein, people thought mass and energy were conserved separately. Einstein showed they are two forms of one thing, so mass can turn into kinetic energy, heat, or radiation, and back again.
Because c^2 is enormous. c = 3 x 10^8 m/s, so c^2 = 9 x 10^16 m^2/s^2. Multiplying even a small mass by this giant number gives a large energy. Example: 1 gram (10^-3 kg) gives E = 10^-3 x 9 x 10^16 = 9 x 10^13 J. That is why nuclear energy is so large compared to chemical energy.
1 atomic mass unit (u) is a mass. Using E = mc^2, that mass has an energy equivalent of 931.5 MeV (mega electron volt). So instead of converting mass to energy in joules every time, in nuclear physics we directly use: energy (in MeV) = mass change (in u) x 931.5. This shortcut is used in almost every NEET nuclei numerical.
No, it is a universal relation and true for all mass. But the effect becomes noticeable only in nuclear reactions, where the mass change is large enough to release measurable energy. In ordinary chemical reactions the mass change is far too small to detect, so we do not use it there.
Two routes. If mass is in kg, use E = mc^2 with c = 3 x 10^8 m/s to get energy in joules. If mass change is in u, just multiply by 931.5 to get energy directly in MeV. For NEET, the u x 931.5 MeV route is fastest and is what most questions expect.
E = mc^2, where E is energy, m is mass, and c is the speed of light in vacuum (about 3 x 10^8 m/s). It states that mass is a form of energy and can be converted into other forms of energy.
1 atomic mass unit (u) is equivalent to 931.5 MeV of energy. This value comes from applying E = mc^2 to the mass 1 u.
Using E = mc^2, E = 10^-3 x (3 x 10^8)^2 = 9 x 10^13 J. This shows how enormous the energy from even a small mass is.
Albert Einstein proposed it as part of his special theory of relativity. He showed that mass and energy are two forms of the same physical quantity.
Because the mass of a nucleus is slightly less than the sum of its parts (the mass defect). That missing mass is converted into binding energy through E = mc^2, which holds the nucleus together and is released in fission and fusion.
