Light can be thought of as a WAVE
Think about ocean waves:
`` " = ``Wavelength'' =
distance between crests (or any two identical spots). The
units are distance units like ``feet'' or ``meters''.
``f'' or `` '' = ``frequency'' = Number of times a
boat goes up and down per unit time. The units are 1/(time), e.g.
1/second. Sometimes this is stated as ``cycles/second''.
v = speed of the wave. Units of distances/time.
The boat goes up and down with the waves. What about the water?
Q. Just what is traveling in the direction of the waves?
Energy and information. Waves are a disturbance traveling
through a medium (although E-M radiation can travel in
There are other kinds of waves (ocean waves are sometimes called
``gravity waves'' or ``surface waves'')
- Sound Waves: are density/pressure waves.
- The speed of sound in air (on a cool day) is ~1000 feet/second
(this is the basis of the old ``distance of the thunderstorm'' trick).
Do the air molecules travel at this speed?
In a higher-density medium (for example railway tracks) it travels
So, what does this have to do with LIGHT?
- An electrically charged particle has an electric field extending to
infinity. If this charge is accelerated , the position of the field center
changes and that information propogates out as a ``kink'' in the
field lines. A magnetic field is also induced at the kink. This
traveling kink is an electro-magnetic wave.
- The SPEED with which the information that the charge accelerated
travels outward is called the Speed of Light:
Wed Jan 14 23:06:17 PST 1998