Electromagnetic radiation is generated by the vibration of electrons or other electrically charged particles. The energy produced by this vibration travels in the form of electromagnetic waves. These waves are characterised by their wavelength (λ) which is the distance between successive peaks and is measured in units of length, and by their intensity, or amplitude, which is the height of each of those peaks. Wavelength has an inverse relationship to the frequency. More: Waves with different wavelengths and amplitudes: