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Amplitude and Wavelength

The amplitude is the maximum displacement of an oscillating point on the wave from its equilibrium point. Imagine ripples on a pond. A single ripple contains both a peak above the undisturbed surface and a trough below. The amplitude is then either the displacement from the surface to a peak or from a trough to the surface - they are the same. The amplitude is closely related to the energy of the wave. Think of sea waves: on a calm day they lap the shore with a small amplitude, but on a rough day gigantic waves with enormous amplitudes crash into the shore dumping immense amounts of energy. The wavelength is the distance from peak to peak, trough to trough, or between any other two adjacent identical parts of the wave.

The displacement-position graph for a wave is shown. The plot is drawn with a blue line and has a sine curve shape. A red vertical line measures the displacement from a trough to zero and is labelled "amplitude". A second red line measures the displacement from zero to a peak, also labelled "amplitude". The displacements are the same. A green horizontal line measures the distance from one peak to the next peak and is labelled "wavelength". A second green line measures the distance between two successive identical parts of the plot, also labelled "wavelength". The distances are the same. Below this diagram, similar graphs are shown for waves with different wavelengths and amplitudes. For greater wavelengths the peaks and troughs are wider, while for smaller wavelengths they are narrower. For greater amplitudes the peaks and troughs are taller and deeper, while for smaller amplitudes they are shorter and shallower.

Figure 1: Displacement-position graph for a wave.

These properties affect how the wave interacts with the world. For example, the wavelength of visible light dictates the color that we see, while the amplitude of sound waves affects how loud we perceive them to be.