Figure I below shows the lowest four energy levels of an electron in an isolated atom.
I
Figure II below shows the lines in the emission spectrum of the atom that correspond to the transitions of the electron from 
to 
and from 
to .
II
Explain, with reference to photons, why there is a single frequency of electromagnetic radiation that corresponds to each of these transitions.
On Figure II, draw a line that corresponds to the transition of the electron from 
to . Label this line A.
On Figure II, draw a line that corresponds to the transition of the electron from to . Label this line B.
The frequency of radiation represented by line A is 
. The frequency of radiation represented by line B is 
. The energy of the ground state () is 
. Determine an expression, in terms of , , and the Planck constant 
, for the energy 
of the energy level .
of a photon, which is given as:
is the frequency of the radiation and 
