Sound waves in a crystal lattice

Sound waves in a crystal lattice.

An important distinction among different types of waves is how they differ in the relationship between the direction of the oscillation of the disturbances within the wave and its overall direction of propagation. In a longitudinal wave, the wave disturbances oscillate in a direction parallel to the direction of wave propagation. In a transverse wave, the wave disturbances are perpendicular to the direction of wave propagation.

The MCAT often contains a question designed to see if you can identify a common type of wave as transverse or longitudinal. Sound waves are longitudinal pressure waves. However, electromagnetic waves, light, are transverse waves. In an electromagnetic wave, the electric and magnetic field oscillations at right angles to each other and to the direction of propagation.

A light-wave.