The terminology of different parts of the electromagnetic spectrum is given in the text. Use the formula E = hν (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?
The energy of a photon E = hv
Where v is the frequency of the wave.
And, h is planck’s constant = 6.626×10-34J-sec
v is given by the relation v = c/λ,
where c is the velocity of light = 3×108 m/sec
Putting in above formula
E = hc/λ
In electron volts,
eV
eV
⇒ 
eV
The different scales of photon energies obtained are related to the sources of electromagnetic radiation as the different photon energies of the spectrum shows the spacing between the energy levels of the source.