Changes

: [[Refraction]] can occur gradually through a [[medium]] if the [[property|properties]] of that [[medium]] change gradually. This is the case for [[Seismic Wave|seismic waves]] travelling through the [[Earth]] as the [[material]] gets more [[dense]] as you go deeper into the [[Earth]]. This gradually increases the [[Wave Speed|speed]] of the [[wave]]s.

: When a [[wave]] '''refracts''' the [[frequency]] remains constant but the [[wavelength]] and [[Wave Speed|wave speed]] change.

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