"I.N. Galidakis" wrote ...
Post by I.N. GalidakisPost by Richard Crowley"I.N. Galidakis" wrote ...
Post by I.N. GalidakisDoes anyone know an approximate value for the video signal speed?
Alternatively, a camera records images in real time and sends the feed
to
a
monitor connected to the camera with a wire of length L.
After how much time after reception from the camera will the image show
up
on
the monitor?
The speed of electricity is the same as light: 300000 km/sec
But it slows down a bit (~30%) in typical coaxial cables, etc. so only
around 200000 km/sec. That means that an electrical signal can go
around the planet 5 times in one second. For all practical purposes
there is no delay.
Thanks. I am a bit confused because when I search for "speed of electricity" I
http://en.wikipedia.org/wiki/Drift_speed
This is nowhere close to 200000 km/sec. Are we talking about the same thing or
am I misunderstanding something here?
Yes, I should have refered to the propogation speed of the signal
(information), not to the "Speed of Electricity". I just don't give
mollecular physics much thought in my everyday activities. :-)
Drift Speed is the "speed" at which the physical atoms of copper
move. It is zero for all practical purposes. That is clearly NOT the
same as the speed at which the electrical signal moves. Signals move
by pushing (or attracting) adjacent electrons in the copper atoms,
NOT by physically moving the atoms themselves. If fact when
transmitting AC signals (such as audio, video, or mains power)
there is NO net movement because the flow switches direction
very rapidly.
http://en.wikipedia.org/wiki/Speed_of_electricity ....
"The Speed of electricity refers to the *relatively slow movement*
of free electrons or ions through a conductor in the presence of
an electric field, also known as drift velocity. It is often confused
with the *propagation speed of an electromagnetic wave*. It is
the electromagnetic wave that usually conveys information (data),
not the movement of electrons.
Free electrons in a conductor vibrate randomly, but without the
presence of an electric field there is no net velocity. When a DC
voltage is applied the electrons will increase in speed proportional
to the strength of the electric field. These speeds are on the order
of millimeters per second. AC voltages cause no net movement;
the electrons oscillate back and forth in response to the alternating
electric field.[1]
In contrast, electromagnetic wave propagation is much faster, and
depends on the dielectric constant of the material. In a vacuum the
wave travels at the speed of light and almost that fast in air.
Propagation speed is affected by insulation, such that in an
unshielded copper conductor it is about 96% of the speed of light,
while in a typical coaxial cable it is about 66% of the speed of light
[2].