The laws of conservation of energy hold at the subatomic level.
The Principle of Conservation of Energy says that energy can neither be created nor destroyed but changed from one form to another.
In 1905, Albert Einstein said that mass can be converted to energy, this changes the principle slightly but its general meaning remains the same as long as we figure in the energy that mass is equivalent to. So now it is time to use the most famous equation in the whole of physics,
So if any mass in annihilated then this mass turns into energy. Usually the small particles are travelling at great speed, so when we consider the total energy of the reaction we need to recall that the moving energy of the particles is given by
So the total energy before the collision must equal the total energy after the collision.
- Find the Total Mass of the Reactants
- Find the Total Mass of the Products
- Subtract and find the difference in masses
- Calculate the Energy Liberated by using Einsteins E = mc2 formula
A slight adjustment will be needed if the Reactants are moving before hand
- Do the Reactants have any Kinetic Energy, if so factor this in.
This is what was predicted to be true, but in some nuclear processes this was not found to be the case.... such as Beta emissions.
In the case of beta decay, the energy of the emitted electrons is distributed over a given range.
This led to the prediction by Italian physicist Wolfgang Pauli in 1930 that a third particle must be present, he declared that if momentum is not conserved, a third particle must be present.
This new particle takes up some of the energy to make its mass, and more to give it kinetic energy.
This model works as it ensures that energy and momentum are conserved.
This particle was to have no charge as the charges on both sides would not have balanced. The neutrino was named by Enrico Fermi as it means the little neutral one.
The original name given to it by Pauli (the Neutron) was used by James Chadwick to name the bigger particle he had found in the Nucleus in 1932.
The neutrino is neutral, very small and it does not interact with material that often, this led to its discovery taking a long time to verify its existance. In 1956 Clyde Cowan, Frederick Reines, F. B. Harrison, H. W. Kruse, and A. D. McGuire detected the neutrino through this process, a result that was rewarded with the 1995 Nobel Prize.
The law of conservation of momentum holds at the subatomic level too.
The Law states the momentum of all the involved particles before an interaction is equal to their momentum after.
This did not seem to hold true. The velocities of the particles were not usually adding up to the speeds predicted by the conservation of momentum. Wolfgang Pauli predicted there were some very small neutral particles that are also emitted. This would account for the differences in momentum. It was very difficult to detect a small and neutral particle. It was named the Neutrino, after Chadwick had stolen its original name, the neutron for the large neutral particle.
Appropriate calculations to convey sizes and magnitudes and relations between units.
Work is equivalent to energy,
therefore if qV is equal to the work then this is also the amount of energy in a particle.
1 eV = 1e- x 1 V
The charge on an electron (qe) = 1.602×10−19 C
1.602×10−19 C x 1 V
=> 1 eV = 1.602×10−19 J
1keV = 1000 eV = 1.602×10−16 J
1Mev = 1,000,000 eV = 1.602×10−13 J
1Gev = 1,000,000,000 eV = 1.602×10−10 J
You have to be able to convert from Joules to electronVolts and back again.
Questions for you
So how many eV is there in 3.6J ?
how many eV is there in 1 kWh ?