The terminology of different parts of the electromagnetic spectrum is given in the text. Use the formula $E = hv$ (for energy of a quantum of radiation: photon) and obtain the photon energy in units of $eV$ for different parts of the electromagnetic spectrum. In what way are the different scales of photon energies that you obtain related to the sources of electromagnetic radiation?

Energy of a photon is given as:

$E=h v=\frac{h c}{\lambda}$

Where,

$h =$ Planck's constant $=6.6 \times 10^{-34} Js$

$c=$ Speed of light $=3 \times 10^{8} m / s$

$\lambda=$ Wavelength of radiation

$\therefore E=\frac{6.6 \times 10^{-34} \times 3 \times 10^{8}}{\lambda}$$=\frac{19.8 \times 10^{-26}}{\lambda} J$

$=\frac{19.8 \times 10^{-26}}{\lambda \times 1.6 \times 10^{-19}}=\frac{12.375 \times 10^{-7}}{\lambda} e V$

The given table lists the photon energies for different parts of an electromagnetic spectrum for different $\lambda$

$\begin{array}{|l|l|} \hline \lambda(m) & E ( eV ) \\ \hline 10^{3} & 12.375 \times 10^{-10} \\ \hline 1 & 12.375 \times 10^{-7} \\ \hline 10^{-3} & 12.375 \times 10^{-4} \\ \hline 10^{-6} & 12.375 \times 10^{-1} \\ \hline 10^{-8} & 12.375 \times 10^{1} \\ \hline 10^{-10} & 12.375 \times 10^{3} \\ \hline 10^{-12} & 12.375 \times 10^{5} \\ \hline \end{array}$

The photon energies for the different parts of the spectrum of a source indicate the spacing of the relevant energy levels of the source