<P> There are three types of mechanical waves: transverse waves, longitudinal waves, and surface waves . </P> <P> Transverse waves cause the medium to vibrate at a right angle to the direction of the wave or energy being carried by the medium . Transverse waves have two parts--the crest and the trough . The crest is the highest point of the wave and the trough is the lowest . The distance between a subsequent crest and a trough is half of wavelength . The wavelength is the distance from crest to crest or from trough to trough . </P> <P> To see an example, move an end of a Slinky (whose other end is fixed) to the left - and - right of the Slinky, as opposed to to - and - fro . Light also has properties of a transverse wave, although it is an electromagnetic wave . </P> <P> Longitudinal waves cause the medium to vibrate parallel to the direction of the wave . It consists of multiple compressions and rarefactions . The rarefaction is the farthest distance apart in the longitudinal wave and the compression is the closest distance together . The speed of the longitudinal wave is increased in higher index of refraction, due to the closer proximity of the atoms in the medium that is being compressed . Sound is considered a longitudinal wave . </P>

What type of wave is the light mechanical or electromagnetic