Electromagnetic Spectrum

The electromagnetic spectrum (EMS) is the general name given to the known range of electromagnetic radiation. Wavelengths increase from approximately 10-18 m to 100 km, and this corresponds to frequencies decreasing from 3 × 1026 Hz to 3 ×103 Hz.

The image below shows the names given to different regions of the EMS. Note that the visible part of the spectrum, the only type of electromagnetic radiation that we can detect with our eyes, makes up only a tiny fraction of the EMS.

emspectrum.jpg

In a vacuum, all electromagnetic waves travel at the speed of light: c = 299,792,458 m/s. An energy ( E ) can be associated with each region of the EMS using the equation:

$ E = hf $

where f is the frequency and h is Planck’s constant which has the value:

$ h = 6.6260693(11) \times 10^{-34} J s $

The table below lists typical wavelengths, frequencies and energies for different regions of the EMS.

Region Wavelength Frequency Energy
Hard gamma 1 × 10-9 nm 3 × 1026 Hz 1.2 × 1012 eV
Gamma 1 × 10-6 nm 3 × 1023 Hz 1.2 GeV
Gamma/X-ray 0.001 nm 3 × 1019 Hz 12 MeV
X-ray 1 nm 3 × 1017 Hz 120 keV
X-ray/Ultraviolet 10 nm 3 × 1016 Hz 12 keV
Ultraviolet 100 nm 3 × 1015 Hz 1.2 keV
Visible (blue) 400 nm 7.5 × 1017 Hz 3.1 eV
Visible (red) 700 nm 4.3 × 1017 Hz 1.8 eV
Infrared 10000 nm 3 × 1013 Hz 0.12 eV
Microwave 1 cm 30 GHz 1.2 × 10-4 eV
Microwave/Radio 10 cm 3GHz 1.2 × 10-5 eV
Radio 100 m 3 MHz 1.2 × 10-8 eV
Radio 100 km 3 kHz 1.2 × 10-11 eV

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