Matter
Matter is a
collection of charges. On average, matter is electrically neutral.
Light
A beam of light can be approximated by a
plane wave if it is monochromatic (of one color). The fields associated
with a plane wave in free space are pictured below. The electric (E)
and magnetic (B) fields are perpendicular to each other and to the
direction of wave propagation, k. The fields are represented as
vectors. The direction of the field is given by the direction of the
arrow and the length of the arrow is proportional to the magnitude
(strength) of the field at the base of the arrow. The figure below thus
represents the electric and magnetic fields along the horizontal black
line.
The wave propagates to the right along the
k-vector. In a plane wave, the peaks of the waves are all in step (in
phase) in a plane that is perpendicular to the k-vector. At a given
point in space, the fields vary sinusoidally in time. Similarly, at a
fixed time (as shown above, the fields vary sinusoidally in space.
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Plane Waves
The figure below represents a plane wave. The three
surfaces correspond to the planes on which the field strength is
maximum. The distance between these planes is the wavelength.
There are other types of light waves, such
as twisted light, where the surface of constant phase is a corkscrew,
as shown in the figure below.
When the light intensity gets low, the
light appears to be made of quanta of energy, called photons. The
photon has spin angular momentum given by Plancks constant. A twisted
beam of light also has orbital angular moment given by an integer times
Planck's constant.
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