Refraction © Siemens Stiftung 2018 CC BY-SA 4.0 international



The wave front model of refraction on an interface makes it clear why the direction of the sound propagation changes.

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When waves cross over from one medium to another, the speed at which the waves spread changes. Consequently, the wave normals of the incident and broken waves have different directions. With light waves, the change in the index of refraction at the boundary is the cause; with sound waves, it is the change in the density.
The graphic illustrates the case when the speed of propagation becomes slower at the transition from the first to the second medium: The wave is broken at the perpendicular of the boundary surface.
An explanation of this phenomenon is provided by the Huygens' Principle: Every point on a wave front is the starting point for a new wave, known as an “elementary wave". The enclosing end of the elementary wave creates the new wave front.

Information and ideas:
Refraction at boundaries also occurs with sound waves (for example, in the atmosphere at the transition from warm to cold layers of air).

Relevant for teaching:
Sound/acoustics: parameters
Vibrations and waves
There are no other media directly related to this file.
Information sheet
Grade 7 to 9; Grade 10 to 13
Middle/high school; Vocational training
Light; Optical refraction; Optics; Sound; Wave (physics); Geometrical optics; Light (basic phenomenon); Refraction; Sound (basic phenomenon); Sound propagation; Sound wave; Wave optics
Siemens Stiftung Media Portal
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© Siemens Stiftung 2018
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