(a)[2]
Using photons in your explanation, explain why each of these transitions corresponds to just one frequency of electromagnetic radiation.
(b(i))[2]
On Fig. 8.2, add a line for the electron transition from $n = 2$ to $n = 1$. Mark this line A.
(b(ii))[2]
On Fig. 8.2, add a line for the electron transition from $n = 3$ to $n = 2$. Mark this line B.
(c)[2]
The frequency of the radiation represented by line A is $f_A$. The frequency of the radiation represented by line B is $f_B$. The energy of the ground state ($n = 1$) is $E_1$. Find an expression, in terms of $f_A$, $f_B$, $E_1$ and the Planck constant $h$, for the energy $E_3$ of the energy level $n = 3$.