Speed of Light and Electricity?, Is Speed of Light and Electricity equal?

Hello,
Correct me if I am wrong:

the speed of light = 299 792 458 m / s

How fast does electricity travel? For example, if you have a 1000 foot long wire, from point A to B, how fast will it take the electricity to go from point A to B?

Does electricity travel at EXACTLY the same speed as light?

Or is it a little bit slower?

Does anybody know the EXACT speed of electricity?


Thank You

Light is a propagating electromagnetic field in open space. The speed of light is the speed of propagation of the electric and magnetic fields that make up the light.

But the speed of light in open space is one thing, and the speed of an electromagnetic field inside matter, in this case a wire, is another; it's slower. That's because it interacts with all the atoms in the matter as it moves along. Each interaction takes a brief moment in time, and the electromagnetic field isn't moving while it's interacting.

Now, these interactions are very, very fast- they don't slow the electric field down very much, no more than a few percent. So the speed of electric current through a wire is very close to the speed of light in a vacuum, but just a bit less.

Remember that it isn't a matter of electrons moving from one end of the wire to another; instead, the electromagnetic field moves through the wire, making electrons jump from one atom to the next, and then another electron from that atom to the next, in a wave. That's how electricity moves through a wire.

You can approximate the speed of light as about a foot per nanosecond. That means if you have a 1GHz Pentium chip in your computer, in the time it takes for it to complete one cycle and execute one machine instruction, the electricity that's making it work has time to move about a foot.

The exact speed of the electromagnetic field through a wire depends on the exact composition of the wire, and on its thickness, and on whether it's in an electromagnetic field from the Earth, or from other wires around it, or from a magnet somewhere nearby, and so forth. So there's no exact answer to give to your question; it depends on the circumstances. But the approximate answer is, it's very, very close to the figure you quoted, just a few percent short of it.

Thank you very much Schneibster.

How about this then: If that 1GHz Pentium chip used optical methods to execute the machine intstructions instead of electronic methods, will its speed be very much faster? Would'nt this be so since light would not be affected by electromagnetic fields? Would it then become perhaps a 2 GHz chip or even faster? Or would the speed of the processor not be enhanced very much?

It would only make a few percent difference; the point of using optical chips isn't because light can move faster than electricity, because for all intents and purposes it can't. The point of using optical chips is that they can make them smaller, which means fitting more onto a single wafer; that makes them both less expensive and faster, because they're closer together.

When I was in the industry, 1GHz was a dream; now they're making chips that run at more than 3GHz. I have a pair in the system I'm writing this on. But there was concern at that time that we were getting pretty close to the diffraction limits of visible light; you have to understand that chips are made using photolithography, which means that the smallest line you can draw is limited by the wavelength of light you're using.

Visible light is relatively safe; if someone gets exposed, they'll probably be OK. But in order to get below about .25 microns line width, you have to use ultraviolet light. This presents two dangers: first, ultraviolet light can burn you, and second, you can't see it. So you could be exposed, and it would burn your retina, and you wouldn't know for a while, a few minutes maybe- and then all of a sudden you're blind. The liability implications of this are a major problem. Safety is a huge concern in chip-making; you have to get insurance to run a chip factory, and the more dangerous stuff you have around, the harder it is to get insurance and the more expensive it is once you get it.

Now, there was talk about using photolithography processes with visible light that used diffraction or perhaps interference to make lines smaller than .25 micron. And if that's what they're doing, then well and good; but at some point, you are going to reach the limits of that method too; and then you have to go to ultraviolet.

There are other problems with ultraviolet; it's higher-energy, so it can damage the silicon. Not much point in making chips that don't work because the very light you're using to make them damages them, right? Worse yet, a lot of glass is opaque to UV. So how do you focus it, how do you reflect it, and how do you use it to make chips?

ETA: I just went onto Intel's site. They are involved in a consortium that has actually produced a deep UV (they are calling it "EUV," Extreme UV- of course, gotta get that "X" in there so everybody gets all excited and buys, buys, buys) chip production plant, including DUV photolithography. Their current process is 65nm (that's 0.065 microns- about one quarter the size I was working with of 0.25 micron) and they project being able to go below 20nm with that technology. So it looks like they've figured out a lot of the problems.

But if you can use light, then a whole bunch of science will let you do things that you can't do with silicon; the only problem is, those things are science, not technology the way making silicon chips is. We have decades of experience making silicon chips, and no experience at all making whatever we'll have to make to use light instead of electricity. So it's not something that's going to be happening any time soon. But we'll have to go there eventually; we'll have no choice. I'm guessing it's a decade or more away, though. By Moore's Law, the current DUV technology appears ready to take them at least that far.

I was reading a article in NewScientist.com about how Electric signals can be transmitted at least four times faster than the speed of light. Now also it has said we can send light signals faster the speed of light over a few meters. But only with the aid of complicated and very expensive equipment. The article said that physicists at middle Tennessee state University have broken that speed limit over distance of nearly 120 meters. By using 120-meter-long cable by alternating six- to eight-meter-long lengths of two different kinds of coaxial cable, each with a different electrical impedance. Then hooking them up to two signal generators, one of which broadcast a fast wave, the other a slow one. The waves interfere with each other to produce electric pulses, which can be watched using an oscilloscope. Now any pulse, whether electrical, light or sound , can be imagined as a group of tiny intermingled waves. The energy of this “group pulse” rises and falls over space, with a peak in the middle. The different electrical resistance in the hybrid cable causes the waves in the pulses rear to reflect off each other, accelerating the pulses peak forward. Using the oscilloscope to trace the pulse strength and speed, the confirmed they have sent the signals peak tunneling through the cable at more than four billion kilometers per hour. Now that it was only the peak moves faster than light speed and not the total energy of the pulse does not . doesn’t that show that we are one step close to breaking Einstein’s relativity theory.

I read that electrons travel at 1/3 light speed, in a vacuum. However, when they are in a wire, and there are collisions and interactions going on like crazy, then that speed is significantly reduced, albeit still fast enough so that when you turn on a switch, your clock lights up pretty much instantly

That's a cool experiment you're describing Haunted07, but if i got it right it was made inside a coaxial cable? C is defined as a photon's speed traveling through space and according to Einstein it seems to be an absolute velocity. Nothing can go faster than that. If you're talking about electricity you just have to read Schneibster's postings to see that it will be slower. and if you let light go through any other medium (glass water gas) then the photons speed will slow down and physicists will time after time prove that they can make f ex light go faster through that medium than it normally are supposed to do. There is a very nice thread about phase velocity or group velocity by Guest_carbonlife at http://forum.physorg.com/index.php?showtopic=6487
It discusses why even though 'something' might seem to travel faster than light the information doesn't.

This post has been edited by yor_on on Jul 2 2007, 07:11 PM

I basically agree with light and electricity in a cable propagating at similar speeds, one being made slower by the refractive index and the other by permittivity and permeability - which in fact build the refractive index at higher frequencies.

I disagree with refraction or permittivity being caused by absorption and delayed emission. It seems that a popular textbook spread this false idea. No delay here, it's the instantaneous permittivity that does it.

Electrons travel in vacuum at any speed between zero and C, both limits excluded.
In a metal, electrons travel very slowly, but their interaction very quickly.

Now, optical chips: That's less simple.
Optics would waste much room on a chip, as guides must be half a wavelength wide or thick (at medium's speed): Say, 200nm instead of today's 50nm wires. Clearances are even worse.

But within a chip (not on the board between the chips), electrical signals are slow. This is because propagation speed is limited by the resistance of the metal tracks (combined with their capacitance) much more than by their inductance. This makes for a speed much smaller than light, and for propagation times that increase as the square of distance. Worse, this time isn't reduced by better and smaller fabrication processes, because thinner conductors increase the resistance: This explains why processor frequencies haven't increased since the Pentium 4, and are currently decreasing with the Core 2.

Optical signal paths will be faster within chips since resistance doesn't affect them. This issue is so crucial to chips today that the industry invests a huge research time in it (it's difficult because silicon is the right material for data processing but the wrong one for light emitters) and chip designers are ready to lose precious room on the chips to accommodate optic buses at least for some long signal paths.

From propagation time, optics would enable to regain the frequency increase we missed for over 5 years, which means a lot. Then we would need to dissipate the heat produced by faster chips - or make smaller chips with the same computing power.

Sorry Enthalpy. I Did not mean it to sound that if there was definite proof that electricity in its 'purest' form couldn't move as fast as light. Tell me, to what do you define this 'instantaneous permittivity' that are 'slowing' emissions? this resistance. Why shouldn't absorption be included?

This post has been edited by yor_on on Jul 3 2007, 01:53 PM

Permittivity slows electric signals (or light, as it increases the refractive index) by increasing capacitances. There is no delayed photon emission mechanism here.

Slower transmission is different from losses. Silica of a fiber slows light by a factor of 1.5 but still carries light over the length of Australia without needing a repeater.

Wouldn't you have to have a better understanding of what electricity actually is to answer to question at hand?

What is electricity? I don't believe anyone really knows. Sure, there are theories, but no solid proof.

At what voltage does electricity actually approach the speed of light? Is it 1 volt? 250k volts? How much voltaic pressure,(difference potential) would it take to alter the speed of electricity?

Does an electron need the presence of a proton to emit EM wave energy? My quick answer is no. On the flip side, bare protons cannot emit EM wave energy, allegedly.

Does an electron need the presence of a proton to generate 'electricity?' You bet your ***.

Pretty sure that electrons travel very slow, at least they do in my plasma ball, which is nitrogen injected. Which brings up the fact that the presence of matter is required for electricity, where light requires no matter to travel in empty space.

These are 2 separate energies. It's my opinion that integrating light and electricity too close together in an effort to understand either is counterproductive in understanding their intricacies.

Hold the phone dudes!

What word on "drift velocity"????

I was lead to believe that electrons move pretty dam slow! It's only cause they shunt each other along (like train cars) that it appears to move fast..

Or are ye's talkin purely waves or some other exotic shizz?!

i think electricity travel speed depend from wire

1. We know what electricity is. It is the flow of charged particles. Voltage is joules per coulomb. That is, energy per bunch of particles. Energetic particles exhibit a higher voltage. generally we think of flow of electrons. Electrons travel slowly through wire. The effect of the voltage travels quickly. Kind of like turning on a hose. Or pushing on a pipe full of ping-pong balls. The actual drift speed of electrons through a 0.5mm wire carrying 5 amperes (5 coulombs per second) is about 1mm per second. Remember that electric current can also be due to the flow of ionized molecules (like in a lead acid battery) or positively charged particles (protons, for example)

2. The voltage has nothing to do with the speed of electricity through a wire. The velocity of propagation (look that up on wikipedia) is determined by the inductive and capacitive characteristics of the wire carrying the electricity. Generally a copper wire is about .75c or less. Light in a vacuum is 1.014ns per foot. But, maybe that is not the question you are asking.
The speed of electrons through free space is affected by their energy, therfore their voltage. A 30,000 volt CRT accelerates electrons to about 0.3c.
The stanford linear accelerator accelerates electrons to .9999+c at 51 GeV

3. A traveling electron constitutes a current, and therefore produces an magnetic field. I consider a traveling proton to be a traveling charge also and therefore it will produce a magnetic field.

4. An electron beam is electricity (like in a CRT monitor or TV set) and that electron beam constitutes electricity. A traveling electron IS electricity, in and of itself. Electricity (electrons) can travel through a vacuum so matter is not required.

5. The electrons in your plasma ball travel pretty fast. The patterns they make change "slowly", but the electrons are pretty quick (maybe .01C, assuming 3,000 volts). Not something you can see.

Electricity is about current flow. There is a difference between current flow and electromagnetic fields. Current flow causes electromagnetic fields. Light is electromagnetic radiation. So, yes, keep them separate.

Speed of light is ~3*10^8 m/s and speed of electricity is at least 2.8*10^8 m/s. They are almost equal...