Nature of light
Light is transverse, electromagnetic wave
motion that can be detected with the human eye.
Sources
Light is produced by one of two methods:
-
Incandescence is the emission of light
from "hot" matter (temperature T ≳ 800
Kelvins),
-
Luminescence is the emission of light
when excited electrons fall to lower energy levels
.
Speed
Like all electromagnetic waves, light can travel through
vacuum. The speed of light in vacuum is represented by the
letter c from the Latin celeritas —
swiftness. The speed of light in vacuum is fixed at
299,792,458 m/s and this fundamental quantity is related,
for instance, to the current definition of the meter. The
speed of light in a medium is always slower than the speed
of light in vacuum. The speed of light depends upon the
medium through which it travels. The speed of anything with
a mass is always less than the speed of light in vacuum.
Light and colours
The amplitude of a light wave is related to its intensity.
Intensity is the absolute measure of a
light wave's power density.
Brightness is the relative intensity as
perceived by a typical human eye.
The frequency of a light wave is related to its color.
Monochromatic light is described by only
one frequency. Laser light is effectively monochromatic.
There are six colors each associated with a band of
monochromatic light. In order of increasing frequency they
are red, orange, yellow, green, blue,
and violet.
Polychromatic light is described by many
different frequencies. Nearly every light source is
polychromatic. For example, white light is polychromatic.
Adapted from //physics.info/light/
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