Transverse wave
Transverse plane wave
A transverse wave is a moving wave that consists of
oscillations occurring perpendicular (or right angled) 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 y–z
plane. Light is an example of a transverse wave.
Explanation
Transverse waves are waves that are oscillating perpendicularly to
the direction of propagation. If you anchor one end of a ribbon or string and
hold the other end in your hand, you can create transverse waves by moving your
hand up and down. Notice though, that you can also launch waves by moving your
hand side-to-side. This is an important point. There are two independent
directions in which wave motion can occur. In this case, these are the y
and z directions mentioned above.
'Polarized' waves
If you carefully move your hand in a clockwise circle, you will
launch waves that describe a left-handed helix as they propagate away.
Similarly, if you move your hand in a counter-clockwise circle, a right-handed
helix will form. These phenomena of simultaneous motion in two
directions go beyond the kinds of waves you can create on the surface of water;
in general a wave on a string can be two-dimensional. Two-dimensional
transverse waves exhibit a phenomenon called polarization. A wave produced by moving your
hand in a line, up and down for instance, is a linearly polarized wave, a special case. A wave
produced by moving your hand in a circle is a circularly polarized wave, another special
case. If your motion is not strictly in a line or a circle your hand will
describe an ellipse and the wave will be elliptically polarized.
Electromagnetic waves
Electromagnetic waves behave in this same way, although it is harder
to see. Electromagnetic waves are also two-dimensional transverse waves. Ray
theory does not describe phenomena such as interference and diffraction, which
require wave theory (involving the phase of the wave). You can think of a ray
of light, in optics,
as an idealized narrow beam of electromagnetic radiation. Rays are used to
model the propagation of light through an optical system, by dividing the real light
field up into discrete rays that can be computationally propagated through the
system by the techniques of ray tracing. A light ray is a line or curve
that is perpendicular to the light's wave fronts (and is therefore collinear
with the wave vector). Light rays bend at the interface between two dissimilar
media and may be curved in a medium in which the refractive
index changes. Geometric optics describes how rays propagate through an
optical system.
This two-dimensional nature should not be confused with the two
components of an electromagnetic wave, the electric and magnetic field
components, which are shown in the electromagnetic wave diagram here. The light
wave diagram shows linear polarization. Each of these fields, the
electric and the magnetic, exhibits two-dimensional transverse wave behavior,
just like the waves on a string.
The transverse plane wave animation shown is also an example of linear polarization. The wave shown could occur
on a water surface.
Examples
Examples of transverse waves include seismic S (secondary)
waves, and the motion of the electric (E) and magnetic (M) fields in an
electromagnetic plane 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.
