In quantum mechanics we deal with the microscopic particles like, electron, proton, neutron and alpha particles. When we say deal it means the dynamics of these particles, from that we observe the velocity, momentum, energy etc of the particle.
In the classical mechanics one observe the energy in continuous form while in quantum mechanics it is in discrete form. Discrete means as you know that quanta is the smallest packet of energy and in the quantum mechanics we deal energy in terms of quanta E=hv. One can found the total number of photons emitted in respect to the specific energy.
A simple notes along with some numerical problems are explained here. You can download the notes by click the google short link.
For any problem you can message in the box..