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Amplitude and intensity
Beginner
Intensity is proportional to amplitude squared.
I ∝ A²Amplitude is the maximum displacement. Intensity (power per area) is proportional to amplitude squared (and frequency squared). Doubling the amplitude gives four times the intensity.
Sound twice as loud in amplitude carries four times the power.
Intensity isn't amplitude.
In more detail
The amplitude of a wave is its maximum displacement from equilibrium. Intensity is proportional to the square of the amplitude and gives the power per unit area carried by the wave.
Real-world uses
- Louder sounds have larger amplitude and carry more intensity.
- Bright light corresponds to a higher intensity wave.
- A loud sound has a larger amplitude than a quiet one, and its intensity is larger by the square of the amplitude ratio.
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Frequently asked questions
Does amplitude change the speed of a wave?
No. Speed depends on the medium, not the amplitude in a linear system.
How does intensity relate to amplitude?
Intensity is proportional to amplitude squared.
Is intensity the same as amplitude?
No. Intensity depends on amplitude squared, so doubling the amplitude increases the intensity by a factor of four.
Related topics in Waves & Sound
Transverse waves · Longitudinal waves · Wavelength, frequency, speed · Wave equation (travelling) · Wave number · Wave speed on a string