Is e=mc2 means that a mass have certain amount of energy in it or it states what energy it can produce 

If it states what energy it has the while transfer of energy mass should also transfer

Asked by vanshikasejwani12 | 1st Sep, 2021, 05:27: PM

Expert Answer:

Einstein mass-energy relation E = m c2 shows the equivalence of mass and energy .
 
It means mass is converted to energy and energy is converted to mass .
 
In both the cases we use the above relation E = m c2 so that to get the conservation of mass and energy together .
 
But this is happening only in nuclear reactions but not in chemical reactions and energy conversion process
like mechanical energy to electrical energy in power production or electrical energy to mechanical energy in motors .
 
Fission reaction that occurs in nuclear reactor is nuclear reaction. When energetic neutron bombards the Uranium nucleus ,
Uranium nucleus is split into fission fragments like Barium and krypton nucleus in addition to energetic neutrons .
 
Hence if we find the total mass of ( neutron + uranium nucleus ) before fission reaction and
mass of ( fission fragments nucleus + neutrons ) ,
 
we find there is a mass difference Δm and this mass difference gives energy  ( Δm c2 ) in the form of kinetic energy of neutrons.
 
Energy production in stars and sun is due to fusion reaction .
In this fusion reactions 4 hydrogen nucleus reacts and give a helium nucleus and positron
 
If we find the mass of 4 hydrogen nucleus and mass of helium nucleus , there is a difference of mass Δm .
This mass difference Δm gives energy ( Δm c2 ) in the form of electromagnetic radiation.
 
Electron and positron combine together , then γ-ray which is electromagnetic radiation is produced .
This is called annihilation of mass into energy .
 
Similarly energetic Gamma ray is converted into electro-positron pair , that is known as pair production.
In pair production energy is converted into mass.
 
In chemical reactions and physical processes , we have mass conservation and energy conservation separately .
 
Whereas in nuclear reactions we do not have mass conservation alone or energy conservation alone .
 
we need to find (mass+energy) conservation together . If some mass  m is converted then we have energy  E = mc2
 
If energy is converted then we have mass Δm = (E/c2 ) . This is called mass-energy equivalence.
 
In conclusion, if mass is converted to energy in nuclear reactions, it is in the form of kinetic energy of product masses
as in the case of fission reaction.Some electromagnetic radiation in the form of γ-rays also produced .
But maximum amount energy appears in the form of kinetic energy of neutrons
 
Alternatively , if mass is converted to energy in nuclear reactions, it may be in the form of electromagnetic radiation
as in the case of fusion reactions occuring in stars . Here also positrons are produced as product masses that has some kinetic energy
but major part of energy appears in the form of electromagnetic radiation .
 

Answered by Thiyagarajan K | 1st Sep, 2021, 08:22: PM