Waves

A wave has frequency in hertz (Hz) equal to the number of complete wave cycles that pass a given point per second. Electromagnetic waves encompass gamma rays through to radio waves, all travelling at the speed of light (in a vacuum) with wavelengths of less than 10⁻¹¹ m (>30 EHz gamma rays) up to 100 km (3 kHz radio waves). Wavelength sets the colour that we see of visible light; frequency sets the pitch that we hear of audible sound, travelling through a medium such as air or water at the speed of sound; amplitude sets the magnitude that we feel of seismic waves through rock.

Timeline of the Human Condition, 1865