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 - Physics


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" = "hv" = ("hc")/lambda`


h = Planck’s constant = 6.6 × 10−34 Js

c = Speed of light = 3 × 108 m/s

λ = Wavelength of radiation

∴ E = `(6.6 xx 10^-34 xx 3 xx 10^8)/lambda`

= `(19.8 xx 10^-26)/lambda` J

= `(19.8 xx 10^-26)/(lambda xx 1.6xx10^-19)` J

= `(12.375 xx 10^-7)/lambda "eV"`

The given table lists the photon energies for different parts of an electromagnetic spectrum for different λ.

λ (m)








E (eV)

12.375 × 10−10

12.375 × 10−7

12.375 × 10−4

12.375 × 10−1

12.375 × 101

12.375 × 103

12.375 × 105

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

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Chapter 8: Electromagnetic Waves - Exercise [Page 286]


NCERT Physics Class 12
Chapter 8 Electromagnetic Waves
Exercise | Q 8.9 | Page 286
NCERT Physics Class 12
Chapter 8 Electromagnetic Waves
Exercise | Q 9 | Page 286

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