amplitude

In physics, maximum variation of an oscillation from the equilibrium value. In a transverse wave motion, such as an ocean wave, it is the height of a crest (or the depth of a trough). In an electromagnetic wave (which is also transverse), it is the maximum intensity of the electric or magnetic field. For a longitudinal wave, such as a sound wave, amplitude is the maximum distance a particle moves from its resting position. A quiet sound has a lower amplitude and a loud sound has a higher amplitude. For a louder sound, more sound energy enters the ear every second. Amplitude is generally denoted by a.

AM (amplitude modulation) radio broadcasting is a method of transmitting audio-frequency signals. The amplitude of the low-frequency audio signal is made to modulate (vary slightly) the amplitude of a continuously transmitted radio carrier wave of a higher frequency. In this way the modulating signal is imprinted on the carrier wave.