Ncert Exercises & Solutions

8.9 The terminology of different parts of the electromagnetic spectrum is given in the text. Use the formula $E = hν$ (for the 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?

Hint: $E=h\nu =\frac{hc}{\lambda }$
Step 1: Find the energy of a photon.

$As, E = hν = \frac{hc}{λ}$

Where, Planck’s constant, h = Speed of light, c =

$\begin{array}{l} E = \frac{6.6 \times 10^{- 34} \times 3 \times 10^{8}}{λ} = \frac{19.8 \times 10^{- 26}}{λ} J \\ = \frac{19.8 \times 10^{- 26}}{λ \times 1.6 \times 10^{- 19}} = \frac{12.375 \times 10^{- 7}}{λ} e V \end{array}$

Step 2: Find the energies of photon for different parts of an electromagnet spectrum.
For different parts of an electromagnet spectrum, the photon energies are given by:

$λ$ (m)	10³	1
E (eV)

The photon energy obtained for the different parts of electromagnetic spectrum shows the spacing of energy levels of the source.

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