If the amplitude of a sound wave is doubled, the intensity of the sound increases by a factor of four.

Here's why:

* Intensity is a measure of the power of a sound wave per unit area.

* Amplitude is the maximum displacement of a particle from its resting position.

* Intensity is proportional to the square of the amplitude.

Therefore, if you double the amplitude, you square that value (2 x 2 = 4), resulting in a fourfold increase in intensity.