Intensity is proportional to the square of amplitude

Progressive Waves — AQA A-Level Physics

I \propto A^{2}

$I$: intensityThe powerThe rate of energy transfer. Measured in watts (W). transmitted per unit area perpendicular to the wave direction. Measured in W m⁻². Proportional to amplitude squared. (W $m^{-2}$)
$A$: amplitudeThe maximum displacement of a point on a wave from its equilibrium (rest) position. Measured in metres (m). (m)

IntensityThe powerThe rate of energy transfer. Measured in watts (W). transmitted per unit area perpendicular to the wave direction. Measured in W m⁻². Proportional to amplitude squared. is the powerThe rate of energy transfer. Measured in watts (W). per unit area carried by a wave.
The energyThe capacity to do work. Measured in joules (J). transferred by a wave is proportional to the square of its amplitudeThe maximum displacement of a point on a wave from its equilibrium (rest) position. Measured in metres (m)..
Doubling the amplitudeThe maximum displacement of a point on a wave from its equilibrium (rest) position. Measured in metres (m). quadruples the intensityThe power transmitted per unit area perpendicular to the wave direction. Measured in W m⁻². Proportional to amplitude squared..
This relationship is used when comparing constructive interference (increased amplitude) with destructive interference (zero amplitude).