Physics. How Can The Speed Of Electricity Be Calculated?

Physics. We Know The Speed Of Sound And Light, But How Fast Does Current Travel Through Wires For Example. Does The Resistence, Voltage, Or Amps Have

Physics : How Can The Speed Of Electricity Be Calculated

We know the speed of sound and light, but how fast does current travel through wires for example. Does the resistence, voltage, or amps have anything to do with it? ~~~ Kemikal ~~~

Best Answer To Physics Question

The speed of electricity is a tricky concept. There are two speeds, not just one. The first speed is the electron drift. The second is the wavefront speed. Electron drift is where the free electrons, not attached to the atoms of the material in which the electrons are found (., a copper wire), actually move as a group in the direction from the negative end, where there is an excess of free electrons, to the positive end, where there is a dearth of free electrons. [See source.] The drift velocity v = mu E; where mu is the so-called electron mobility and E is the electrical field in volts/m or volts/cm. A typical drift velocity is v = 1,000 (120/100) = 1,200 cm/ silicon (Si) at 300 deg K and a field E = 120 V/m. Si has an electron mobility of mu = 1,000 cm^2/volt-sec In mph, Si v ~ 30 mph...way slower than light speed. Amps, the current unit, is directly related to electron drift velocity. In fact amps are just so-many electrons (and their charges) traveling through a conductor over a period of time. Thus, as v = mu E, we can see that as E (the volts/m) is increased the velocity is increased and more electrons flow over time. That is, the amps go up with increasing voltage. And, lo and behold, we learned in basic science that I = V/R and now we know why...electron drift velocity varies with voltage. Also note, R, the resistance, has as lot to do with the current I. So that means, it has a lot to do with the electron drift velocity as drift velocity determines I...higher R slows drift velocity down for a given voltage. Now to the wavefront velocity, which is also called propagation velocity. This speed is what gives us nearly instantaneous on/off control over lights for example. As an electro-magnetic wave, just like for light, the electron wave travels at the speed of light for whatever medium the electrons are confined to. Check this out... "In contrast [to electron drift velocity], 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 in a copper conductor is about 2/3 the speed of light" [See source.] In general, the speed of light is medium dependent. Even so, it is always slower in any other medium than in a vacuum. That is, light speed and other EM waves travel the fastest in a vacuum. From the above quote, we see that the wavefront velocity in copper is about 200,000 km/sec...about 2/3 the speed of light in a vacuum. So the EM wave travels almost instantaneously to the light bulb end of the wire and starts the free electrons near the light bulb to move with drift velocity v. And these now drifting free electrons moving into the bulb filament are what provide the current and power to light up that filament. And let there be light....

All Answers To Physics Questions

Answer 1

It's called "drift velocity" and it's quite slow and well documented. Yes, voltage and so on has an effect, also the size of the wire, composition and just the fact that electrons vibrate wildly and very fast. They do not sit idle and wait to be pushed around and move smoothly. They bump into each other as they travel. I did a calculation in grad school and found that in about 20-30 feet of wiring it would take (roughly) 40 hours for a single electron to travel from the wall switch, up to a fluorescent bulb on the ceiling of the lab I was in at the time. Even tho a single electron does not transit this distance quickly, you have many, many, many electrons traveling per unit time, so the net effect is 'instant' current moving at 'light speed'.

Answer 2

I believe the material separating the two conductors slows it down as compared to just air. Also, the frequency of the signal like 50 HZ or 60 Hz effects the speed.

Answer 3

The speed of electricity is a tricky concept. There are two speeds, not just one. The first speed is the electron drift. The second is the wavefront speed. Electron drift is where the free electrons, not attached to the atoms of the material in which the electrons are found (., a copper wire), actually move as a group in the direction from the negative end, where there is an excess of free electrons, to the positive end, where there is a dearth of free electrons. [See source.] The drift velocity v = mu E; where mu is the so-called electron mobility and E is the electrical field in volts/m or volts/cm. A typical drift velocity is v = 1,000 (120/100) = 1,200 cm/ silicon (Si) at 300 deg K and a field E = 120 V/m. Si has an electron mobility of mu = 1,000 cm^2/volt-sec In mph, Si v ~ 30 mph...way slower than light speed. Amps, the current unit, is directly related to electron drift velocity. In fact amps are just so-many electrons (and their charges) traveling through a conductor over a period of time. Thus, as v = mu E, we can see that as E (the volts/m) is increased the velocity is increased and more electrons flow over time. That is, the amps go up with increasing voltage. And, lo and behold, we learned in basic science that I = V/R and now we know why...electron drift velocity varies with voltage. Also note, R, the resistance, has as lot to do with the current I. So that means, it has a lot to do with the electron drift velocity as drift velocity determines I...higher R slows drift velocity down for a given voltage. Now to the wavefront velocity, which is also called propagation velocity. This speed is what gives us nearly instantaneous on/off control over lights for example. As an electro-magnetic wave, just like for light, the electron wave travels at the speed of light for whatever medium the electrons are confined to. Check this out... "In contrast [to electron drift velocity], 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 in a copper conductor is about 2/3 the speed of light" [See source.] In general, the speed of light is medium dependent. Even so, it is always slower in any other medium than in a vacuum. That is, light speed and other EM waves travel the fastest in a vacuum. From the above quote, we see that the wavefront velocity in copper is about 200,000 km/sec...about 2/3 the speed of light in a vacuum. So the EM wave travels almost instantaneously to the light bulb end of the wire and starts the free electrons near the light bulb to move with drift velocity v. And these now drifting free electrons moving into the bulb filament are what provide the current and power to light up that filament. And let there be light....

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