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Physics Ncert Solutions Class 12th Physics Class 12th Electromagnetic Waves

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

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Payal Gupta | Contributor-Level 10

3 months ago

8.9 Energy of a photon is given as:

E = h $ν$ = $\frac{h c}{λ}$ , where

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

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

$λ$ = wavelength of radiation

Hence, E = $\frac{6.6 \times 10^{- 34} \times 3 \times 10^{8}}{λ}$ J = $\frac{1.98 \times 10^{- 25}}{λ}$ J = $\frac{1.98 \times 10^{- 25}}{λ \times 1.602 \times 10^{- 19}}$ eV = $\frac{1.236 \times 10^{- 6}}{λ}$ eV

The following table lists the photon energies for different parts of an electromagnetic spectrum for different $λ$

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