)
That is L = nh/2p, where n is an integer called the principal
quantum number (c)
The third postulate states that an electron might make a transition
from one of its specified non-radiating orbits to another of lower
energy When it does so, a photon is emitted having energy equal
to the energy difference between the initial and final states The
frequency (n) of the emitted photon is then given by
hn  = Ei – Ef
An atom absorbs radiation of the same frequency the atom emits,
in which case the electron is transferred to an orbit with a higher
value of n