Question

An atom initially at rest, emits a photon of energy E. Find the change in the rest mass
of the atom. Evaluate the result for an atom emitting i)a photon of energy 1eV, ii)a
gamma ray of 1MeV.

Answer 1

whether it be a photon or a gamma ray of 1Mev, the rest mass decreases by the same amount..
In the famous relation E=MC2 , u replace the values of energy as 1Mev (approximately equal to 1.6*106-13 joule) and C (we all know its, 33*10^8 m/s) .. now u'll get M=1.78*106-30 kg approx. this is the decrease in rest mass..

Answer 2

thank you very much

Answer 3

most welcome.. :)