Question

What does amplitude measure?

Answer 1

Amplitude measures the intensity of a wave. On a wave diagram, it is the distance "`a`" from the vertical middle to the crest or trough of the wave:

In terms of sound, it is how loud the sound is:

In terms of light, it is how bright the light is:

In terms of electron orbital probability densities, it is the relative probability electrons are found in those radial coordinates (black is, it can be found more often):