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Glossary of Terms > R


The reduction of a medium's density- the opposite of compression. A sound wave for exapmle is made up of half compression of the medium and half decompression or rarefaction of the medium.


A low voltage lamp used to produce straight edged beams of light for optics lessons. Click here for the Raybox equipment page.

Red shift

Redshift occurs when the light that is emitted from or reflected off of an object is shifted towards the red end of the electromagnetic spectrum.


The return of heat, light, sound etc after hitting a surface.


The change of direction of a ray of light, sound, heat, etc in passing obliquely from one medium into another in which its wave velocity is different.

Ripple tank

A water filled device used to demonstrate the properties of waves. Click here for the Ripple Tank equipment page.