A transverse wave is a moving wave that consists of oscillations occurring perpendicular to the direction of energy transfer. If a transverse wave is moving in the positive x-direction, its oscillations are in up and down directions that lie in the yz-plane. A transverse wave could be represented by moving a ribbon or piece of string, spread across a table, to the left and right or up and down.
The properties of transverse waves are exemplified by ripples in water, the vibrations of a stretched string and electromagnetic waves. In transverse waves, the molecules of the medium oscillate perpendicular to the direction of propagation, whereas in longitudinal waves, the molecules of the medium oscillate parallel to the direction of propagation. In seismology transverse waves are called secondary, or s waves because they arrive later than the primary, or p waves from an earthquake, which are longitudinal. The inability of s- waves to travel through the earth’s outer core shows that it is liquid.
Examples of transverse waves include seismic S (secondary) waves, and the motion of the electric (E) and magnetic (M) fields in an electromagnetic wave, which both oscillate perpendicularly to each other as well as to the direction of energy transfer. Therefore an electromagnetic wave consists of two transverse waves, visible light being an example of an electromagnetic wave. See electromagnetic spectrum for information on different types of electromagnetic waves.
An oscillating string is another example of a transverse wave; a more everyday example would be an audience wave.
In mathematics, transverse waves are associated with the curl and are governed by a vector wave equation, in contrast to longitudinal waves, which are associated with the div operator and are governed by a scalar wave equation. A longitudinal wave exists as compressions moving through the plane in which it is travelling. Energy from this wave is transmitted as mechanical energy. The speed of a transverse wave is determined by the equation "wave speed= frequency x wavelength"