Published by Patrick Mutisya · 14 days ago
Know the main regions of the electromagnetic spectrum in order of frequency and in order of wavelength.
The electromagnetic (EM) spectrum is a continuous range of electromagnetic waves characterised by their wavelength (\$\lambda\$) or frequency (\$f\$). The relationship between them is given by
\$c = \lambda f\$
where \$c = 3.00 \times 10^{8}\ \text{m s}^{-1}\$ is the speed of light in vacuum.
| Region | Wavelength \$\lambda\$ | Frequency \$f\$ | Common Uses / Examples |
|---|---|---|---|
| Radio waves | \$>10^{-1}\ \text{m}\$ (up to many kilometres) | \$<3\times10^{9}\ \text{Hz}\$ | Broadcast radio, TV, mobile communications |
| Microwaves | \$10^{-3}\ \text{m}\$ to \$10^{-1}\ \text{m}\$ | \$3\times10^{9}\ \text{Hz}\$ to \$3\times10^{11}\ \text{Hz}\$ | Microwave ovens, radar, satellite links |
| Infrared (IR) | \$7\times10^{-7}\ \text{m}\$ to \$10^{-3}\ \text{m}\$ | \$3\times10^{11}\ \text{Hz}\$ to \$4\times10^{14}\ \text{Hz}\$ | Thermal imaging, remote controls, fibre‑optic communication |
| Visible light | \$4\times10^{-7}\ \text{m}\$ (violet) to \$7\times10^{-7}\ \text{m}\$ (red) | \$4.3\times10^{14}\ \text{Hz}\$ to \$7.5\times10^{14}\ \text{Hz}\$ | Human vision, illumination, photography |
| Ultraviolet (UV) | \$10^{-8}\ \text{m}\$ to \$4\times10^{-7}\ \text{m}\$ | \$7.5\times10^{14}\ \text{Hz}\$ to \$3\times10^{16}\ \text{Hz}\$ | Sunburn, sterilisation, fluorescent lamps |
| X‑rays | \$10^{-11}\ \text{m}\$ to \$10^{-8}\ \text{m}\$ | \$3\times10^{16}\ \text{Hz}\$ to \$3\times10^{19}\ \text{Hz}\$ | Medical imaging, security scanners, crystallography |
| Gamma rays | \$<10^{-11}\ \text{m}\$ | \$>3\times10^{19}\ \text{Hz}\$ | Radioactive decay, cancer treatment, astrophysics |