Electromagnetic spectrum

The electromagnetic spectrum describes the range of radiation that exists physically. This broadly covers radio waves, infrared, ultraviolet, x-rays, gamma rays, and visible light (which forms a small subset). From left to right, we have waves with the longest wavelengths (and lowest energy) to the shortest wavelengths (and highest energy).

Energy in the electromagnetic spectrum is quantised and proportional to its wavelength:

$$E=\frac{hc}{\lambda }$$

where $h=6.626\times 10^{-34}J$, Planck’s constant, $c=3\times 10^{8}m{s}^{-1}$, the speed of light in a vacuum, and $\lambda$ is the wavelength. Alternatively:

$$E=hf$$

where $f$ is the frequency of the wave.