Essential idea: All waves can be described by the same sets of mathematical ideas. Detailed knowledge of one area leads to the possibility of prediction in another.
Understandings: Amplitude and intensity
Applications and skills: Solving problems involving amplitude, intensity and the inverse square law
Data booklet:
The energy carried by a wave is proportional to the amplitude of the wave. The energy is defined as intensity: the energy per unit time (i.e. power) per unit area transmitted by the wave. In SI units this is generally watts per metre squared.
For all waves studies in this unit intensity is proportional to the amplitude squared.
When any form of radiation, including sound waves, electromagnetic waves, etc., is radiated into three-dimensional space from a point source then the wavefront will spread out in a sphere. Mathematically this means that the intensity of the wave will decrease in proportion to the square of the distance. In other words it is an inverse square law.
Oxford Physics: pages 137 - 138, including a worked example on page 138
Hamper HL (2014): page 186
Pages 193-201, in combination with previous sections test all of this content.