Water waves and sound
waves are examples of mechanical waves. Light waves are not considered
mechanical waves because they don't involve the motion of matter. Most of
the mathematics and properties of mechanical waves apply to light waves.
Light waves are different from mechanical
waves, however, because they can travel through a vacuum. Light waves are
just one type of electromagnetic wave. Other electromagnetic waves
include the microwaves in your oven, radio waves, and
Light waves are regarded as a varying electric field (E) coupled with a
varying magnetic field (B), at right angles to each other and to the
direction of travel. This is depicted in the animation below.
An electromagnetic wave transports its
energy through a vacuum at a speed of about 3.00 x 108
m/s (commonly known as c),
i.e. the speed of light. The whole family of electromagnetic waves extends
from gamma rays of very short wavelength (lower than 10-10 m)
to very long radio waves (greater than 103 m). Just as for
mechanical waves, light waves exhibit reflection, refraction, interference
and diffraction and satisfy the relation
v = f λ.
Unlike transverse waves
such as electromagnetic waves, longitudinal waves such as sound waves cannot be
polarized. The polarization of a wave is given by the orientation of
oscillations in space with respect to the disturbed medium. A polarized
wave vibrates in a single plane in space. Since sound waves vibrate along
their direction of propagation, they cannot be polarized.
cannot be polarized.