Answers
E = m c² is a wrong equation with no explanation .
So here is the correct thing .
E = Δ m c² .
Δ is spelled as delta and it signifies change .
First of all let us talk about the units and then we will discuss about the formula :
E is the energy released .
Δ m is the change in the original and final mass .
c is the speed of light squared here .
E = ( m₂ - m₁ ) c²
Explanation of the formula :
The formula is a relation to show the amount of energy released when an atom disintegrates or loses mass due to nuclear changes .
Nuclear changes means that the changes take place within the nucleus of the atom .
The formula is very important as from this we can prove that the mass of a photon is zero using the formula .
Let the rest mass of a photon be m .
m = E/c² according to the formula .
Now the rest energy will be zero .
⇒ m = 0 .
Another important thing .
E = mc² is incomplete .
Here is the complete formula which was not written by Einstein :
E² = m²c⁴ + p²c²
This is the exact formula for energy .
p = momentum of the body ,
If the body is at rest p = 0 and hence E = m c² .
Only when a body is at rest we apply this formula .