Light is one of the most familiar things in our
lives. We see because we have organs (our eyes) that sense the
intensity (brightness) and wavelength (color) of light. We
experience light in a variety of other ways as well. For example,
we sense radiant heat when our skin is near a warm object. This is
due to our skin's reaction to infrared radiation.
We learn almost all of what we know about the
world around us from the interaction of the objects in the world
with electromagnetic radiation. Often, the word 'light' is used a
little more broadly, to include electromagnetic radiation that is
just outside the range we can see, in the ultraviolet and
infrared.
Light is electromagnetic radiation with a
wavelength that is visible to the eye (visible light) or, in a
technical or scientific context, electromagnetic radiation of
wavelengths that are studied in the field of optics. The three
basic dimensions of light (i.e., all electromagnetic radiation)
are:
-
Intensity (or amplitude), which is related to the human perception
of brightness of the light,
-
Frequency (or wavelength), perceived by humans as the color of the
light, and
-
Polarization (or angle of vibration), which is not perceptible by
humans under ordinary circumstances.
- Under
normal circumstances - i.e. travelling through a uniform medium,
light travels in a straight line. Our visual systems rely heavily
on this fact, 'back-projecting' rays that enter our eyes, to the
probable origin of the light rays. Objects that we see around us
can usually be assumed to be where they appear to be, as long as
the light from them has travelled to our eyes in a straight line.
However, the following phenomena can alter the path or nature of
the light.
1. Matter
