What are Periodic Waves?
A periodic wave is the name given to any repeating pattern with constant wavelength and frequency. We can describe a periodic wave by characteristics such as amplitude, frequency and time period. Examples include sound waves (longitudinal) light waves (transverse) water waves and AC generators.
A sine wave, where y = sin(x) is an example of a periodic wave due to its repeating shape.
The amplitude of a wave, shown as A in the diagram below, is directly related to the energy of a wave, it also refers to the highest and lowest point of a wave.
For instance, if we consider an audio signal, the amplitude is interpreted by the listener as 'loudness' of the noise. The greater the amplitude, the more energy there is to vibrate the ear drum of the listener, which is interpreted as a high energy (loud) noise.