Dispelling a myth

[Diamond187]

I don't what made me think of this, but I just remembered somebody bringing up the fact that electricty moves at the speed of light, but is made of electrons during a discussion about relativity. Well, I just decided I'd clear this mystery up in a new segment I'm introducing: Diamond's Science Trivia (meh, I'm bored).

Alright, while it is true that electricity propagates at the speed of light, it is not true, in the strictest sense, that electricity is made up of electrons. Electricity is actually caused by a movement of charge, not the movement of each individual electron. For example, when you apply a voltage to a conductive wire, your ammeter/voltmeter will read the current/voltage as if the electricity came through at the speed of light (which it did), but this is not because it sees each electron flying by. Each electron in the wire is probably moving at a net rate of about 10^-7 to 10^-12 m/s towards the other end of the wire. But, the conducting wire has vast quantities of these electrons each of which pushes against its neighbour. So, while the electron drift is very slow, the rate of electrical flow is extremely fast.
An easier, more mechanical way to visualize this is by considering a pipe which is completely full of water. If I attach a pump to the pipe, I can make the water goes as fast or as slow as I like by adjusting its power output. However, if I turn that pump on, consider how quickly water a few meters away from the pump starts to move. If you measure how the flow propagates as opposed to what the flow rate is, you'll find the flow initiation propagates at light speed. To us, it seems instantaneous, and how could it be any other way if you consider the water as one rigid object (which it effectively is)? Well, one of the consequences of relativity is that no information can move faster than the speed of light, so instantaneous action is impossible. The water (or electrons) can only react as quickly as physically possible, which is at the speed of light.

Ok, that was probably more confusing than enlightening, but hopefully it got through to those who were curious. Next time, I'll try and explain that pressure problem I had with one of Afterburner's questions (see Fiz's thread on astronomy).

PS. If you have any science based questions (not data questions like 'What's the mass of the Earth?' or 'What's the decay rate of Uranium 235?") feel free to ask and I'll see if I can offer some kind of explanation.

[Rob97]

Brain... throbing....

Anyway, thats pretty interesting.

[Jshall]

Cool so was Eistien wrong when he said nothing can move at the speed of light??

[Starz99cup16]

That kind of science doesnt really interest me

[Trigun747]

Science is ok with me. You just lost me near the bottom though. It was sorta enlightening more or less.

[Diamond187]

Cool so was Eistien wrong when he said nothing can move at the speed of light??

No, that was exactly the point of this post. A lot of people think that electricty is made up of electrons moving at light speed. This post was to explain how electricty moves at light speed and is still composed of electrons.

[The First]

Stupid question: does electricity (the electric charge in this case, not the electrons) really move at the speed of light? Or just an incredibly fast speed we just set equal to the speed of light?

And I still think Einstein had a screw loose in his head... that might be because I can't quite understand how he managed to jump from light having a constant speed, even if the light source moves at a certain speed, to time being dilated and moving quicker and slower and bleh...

[Fiz]

The best way to explain this phenomenon is the way I explained it to my cousins when they asked me this question, which is as follows:

Picture a long tube the size of a football field with a circumference just big enough to hold golf balls. It would look something like this:

--------------------------------------

--------------------------------------

Now, a wire that is used for electrical purposes is already chock full of electrons. In this case, the tube would be filled to the brim with "stationary" golf balls. (Actually, like electrons, the golf balls would be wiggling slightly) That would look like so:

--------------------------------------
OOOOOOOOOOOOOOOOOOO
--------------------------------------

When a current flows through a wire, in essence, all that's happening is a domino effect. The electron that's at the beginning of the wire gets bumped by another electron entering the wire, which causes a "wave" down the line of electrons, pushing the last electron out of the wire and into whatever electronic device you are using. As long as a current is being supplied, the electrons will continue to get bumped into your device.

With the golf balls, imagine standing at one end of the tube and pushing a free golf ball into the tube. This would "instantly" cause the golf ball at the other end to be expelled from the tube.

--------------------------------------
O ->OOOOOOOOOOOOOOOO -> O
--------------------------------------

The more current you push through a wire, the more power you receive on the other end. So technically, electric current is measured as the rate of charge that flows past a given point per second.

And that is how the phenomenon works. Technically then, you can see that electricity does not really move at light speed. Even lightning bolts don't move at the speed of light. To us, however, its inconceivable.

[HavocWizard]

The way I see it, that's all right.

[Diamond187]

I'm fairly sure that electricity does propogate at the speed of light. It was actually what Einstein used to concieve relativity. This is the simple model he used:

Imagine if you will, a field of 3 cows, each of which have their head through an electrical fence, feeding on the grass on the other side. The farmer, seeing the cows eating his neighbour's grass, decides to turn on the electric fence. Einstein observes all this from the opposite side of the fence. ie

Farmer---cow----cow----cow----Einstein

Now, the electricity goes down the fence and shocks each cow in turn. What Einstein sees is each cow jumping up into the air all at the same time. He is amazed by the cows reflexes and talks to the farmer about what he has seen. Amazingly, the farmer is confused by Einstein's story and says, but I saw the first cow jump only once the electricity reach the second cow and the second cow didn't even jump until after the electricty had gone through the whole fence. Befuddled by this Einstein went home to contemplate who was right.

The famous conclusion that Einstein came to was they were both right! The light from each event reached Einstein at the same time the electricity did, since the cows jumped exactly once they were shocked. Of course, the farmer sees the electricity hit the cow, and then the light travels back to the farmer, reaching him only once the electricity has reached the second cow. From that Einstein realized that what is simultaneous in one reference frame is not simultaneous in all other reference frames. So, time must not be absolute, but relative to your frame of reference.

[Fiz]

That's all well and good, and I totally agree with you on reference frames in accordance with time, but that argument can be used for lightning strikes as well. The classic case is similar to what you gave as an example, but involves two people standing at a distance away from each other, both near a tree. If two lightning strikes hit both trees at the exact same time, both would see the tree closest to them as being hit first, and the furthest one being hit second. Different example, same relevance.

The point I'm trying to make here is that just because time is absolute doesn't mean that it can prove whether something moves at light speed or not. As I mentioned earlier, lightning does not move at light speed, despite what people think, but it can be used to explain the argument about time being relative.

The reason I'm saying that electrical signals do not travel at light speed is due to the fact that although the golf balls in a tube theory explains how the signal is transmitted almost instantaneously from point A to point B, it is flawed in its simplicity.

Electrons are actually not as close to each other as you would think. They actually have a very large seperation distance. In fact, the gap between electrons can be as large as one hundred thousand times their diameter. This means that for the transmission of the signal to propogate through the wire, the electrons do have to travel a little bit on their own before they "come into contact" with one another. Actually, they would be repelling each other, since they have like charges. Since the moving electron has momentum (since electrons do have mass), that electron would "push" the next one in line, and so on.

A copper wire also has a resistance associated with it. This resistance will affect how the electrons transmit the signal down the wire. I'm not saying that the actual transmission speed is affected from one interaction to the next, I'm saying that the movement of the individual electrons is affected. In my opinion, the conservation of energy states that energy must be conserved. If the wire heats up, that energy has to be coming from somewhere. Perhaps its coming from the transmission of the electrical signal down the wire, which would mean that some of that energy is being converted.

Magnetic fields also affect the wire, but that's a whole other ball game.

I'm not saying that the transmission is not near light speed, because it is. I'm saying that its not at light speed. At relativistic speeds, the words "at" and "near" make huge differences.

[Liokae]

All electro-magnetic forces propagate at the speed of light. Light itself is an electromagnetic wave. Electric *flow*, however, just gets very close, thanks to resistance.

[invisiblevil]

For instance electrons travel at approx 2/3rds the speed of light through copper. That's about 200,000 km/s... such random posts here. Was this to answer someone's question? Really, while enlightening, these little chats are not nearly as fun as perhaps an internet game? Or perhaps hanging out with your friends. You'll find no great truths in science. What will really piss off some of you physics nuts on these boards is when you find out that all of mechanical physics theory is indeed obsolete... proven incorrect. Eventually you will have to learn all the quantum theory that accounts for most of the differences between theory and reality.... most, but not all, which means that some day that theory will itself be proven incorrect and you will have to start all over again. Why bother? Become a Music or English major while you still can!

[DarkReality]

... *squints* speaking of useless posts....

Somehow, it sounded sarcastic and absolutely pointless. *laughs at the thought of being a music major*

[Fiz]

What will really piss off some of you physics nuts on these boards is when you find out that all of mechanical physics theory is indeed obsolete... proven incorrect. Eventually you will have to learn all the quantum theory that accounts for most of the differences between theory and reality.... most, but not all, which means that some day that theory will itself be proven incorrect and you will have to start all over again.

I would be enlightened to know how this thread could be labelled as a topic discussing mechanical physics. I hope you realize that by discussing the movement of electrons, we are discussing things at a quantum level, and by discussing electricity, we are discussing a topic related to fields and energy. How you got "pissed off" regarding our blind following of mechanical physics seems to lose me somewhat in relation to this thread. :) Don't get me wrong, I'm pretty amused, and I'm not in the least bit upset, cuz I'm a pretty laid back guy. But if you don't have anything intellectual to add to this conversation, I suggest you don't be hypocritical and sarcastic.

Aside from that, what's so wrong in having a discussion about physics on a board designed for online games? If we're offending you, by all means, let us know. Maybe we'll cater to your needs by labelling our posts differently. :lol: Please don't generalize the fact that an intelligent discussion inhibits you from "hanging out with friends" or playing games online. For some people like Diamond and I, (being University students who are over 21) we have already realized that playing internet games isn't going to get you anywhere in life. Having intelligent discussions with your friends, however, can help you in life by making you a well rounded individual.

Lastly, for the most part, physics is both an exact science and a theoretical one. If you don't discuss it, you don't develop new theories, and you don't advance.

But thanks for your opinion. ;) No hard feelings, but if you have thoughts on the physics portion, by all means let us know! That's what we enjoy doing, anyway.

[DarkReality]

Pwned.

I have nothing more to add.

[Diamond187]

Dammit, you so stole my post Dark!

[Fiz]

:lol: Hi-larious!

[huntershadow]

well i belive you are all in your own points both right and wrong in the idea of subspace reptures also know as black holes / worm holes that light cant even escape but for that to be true the force of gravity has to be pulling nothingness faster 186000 miles per second meaning that if einstien was right that the faster you go the slowertime goes would mean that the light would get dispated instantly and................. oh no ive gone cross eyed and im going to start a thread on time travel conondrums right now

[sephiroth4367]

woah too sciency

[Diamond187]

No... no it wasn't...

And this thread was ended so elegantly before. *sigh*

[Fiz]

well i belive you are all in your own points both right and wrong in the idea of subspace reptures also know as black holes / worm holes that light cant even escape but for that to be true the force of gravity has to be pulling nothingness faster 186000 miles per second meaning that if einstien was right that the faster you go the slowertime goes would mean that the light would get dispated instantly and................. oh no ive gone cross eyed and im going to start a thread on time travel conondrums right now


Well...first of all, the problem with that statement is that "light" (in the form of photons) is above our laws of time and space. Second of all, black hole physics is still a young science, and is purely theoretical at this point. Third of all, the gravitational pull of a black hole is indeed so strong that light cannot escape its pull. That doesn't mean much until you look at the escape velocity of a black hole. Its the escape velocity that determines what can escape a body in space. The escape velocity depends on the mass of the object, its radius, and the gravitational constant G. Therefore, an object like a planet, with a large mass and a large radius, has a pretty small escape velocity. An object like a black hole, however, has an extremely large concentration of mass in an extremely small space. That makes the escape velocity so great that you would need to travel faster than the speed of light to escape it...since nothing can travel that fast, nothing can escape.

That's an accurate physics model and until something can travel faster than the speed of light, this theory will remain intact.

[DarkReality]

It's an assumption we can't prove wrong. It therefor is right at the moment.

Hah >_< Sorry, but reading that last sentence made me laugh really hard. Once again, could be lack of sleep.

Question though, if light is above our laws of physics, how does a photoelectrical effect occur? I think I might have even asked this before, but I think I'll just ask again. Is it one of those "it just happens" things?

[Fiz]

The photoelectric effect occurs when a wave of light strikes a piece of metal, and if the energy is great enough, an electron gets knocked from the atom it originated from.

I didn't say that light is above our laws of physics, just time and space. Photons interact with other particles, they just do it at a level that we can't understand. (because of the wave-particle duality)

Light interacts with the Universe with energy transfer, and since the primordial soup that created our Universe relied purely on energy interactions, it makes sense that a fundamental thing like light interacts this way as well.

[Hex]

Correct me if im wrong.
einsteins theory on E=MC squared meaning energy equals mass times the speed of light. This shows that light is both a particle and a wave, meaning it can be affected by forces such as gravity. In fact, this has been proven because during a lunar eclipse, the light is curved by gravity. But, what about when light is turned into other energy, what happens there?

[Fiz]

Actually, during a lunar eclipse, the sunlight that enters Earth's atmosphere is redirected when it interacts with the atmosphere. The photons that are redirected, or "bent", towards the moon reflect off of its surface and produce the red color we see during the eclipse. The reason why light bends in other situations, like near a black hole, is because the shear mass of objects like black holes warp space time, curving it around the super-massive object. The light that travels towards this object travel with the curve created in the space around it.

However, even though light does not have a rest mass (because it never stops moving), it can be thought to have a certain definition of mass...its a really complicated set of theories, but there are arguments for it.