Why electricity flows

reply to post by AthlonSavage

Good post and thread.............very simply stated for us laymen to grasp...........

I hope this response is still simple enough for us to understand. The analogy with a water cistern is okay enough, but to extend your idea of a pipe (hose) might be a little more helpful too. The actual electrons themselves moving through the wire is somewhat misleading. Any movement of electrons is very small and it to be counted in nanometers. I'll try to explain and hopefully add to the OP's already simplified post.

Lets take the pipe/hose part of his analogy to water systems. In a water pipe: one molecule is forced into the pipe, then the disturbance spreads rapidly along the pipe (at speed of sound in the water), and another molecule drops out on the other end.
In wire: one electron pops in, the disturbance spreads rapidly along the wire (at speed close to the speed of light), and at the other end an electron pops out.

The important thing is that electrons move very slowly, but disturbances move fast.

In the vacuum tube electrons move at relatively high speeds. However in the wire, it is much different - the wire is already completely populated with electrons. If you put one extra electron inside, others will fill the jam and will quickly readjust their positions. Electrons won't actually move much, just a few nanometers to reach new equilibrium. But the disturbance will quickly spread along the wire (like a wave).

Electrons 'feel' other electrons because of the negative charge they posses. That's why they don't like 'standing' too close to each other.

When a signal is transferred from point A to point B in a telecommunication wire, it is not that electrons are moved from point A to point B, but instead a disturbance is generated at point A, then the disturbance spreads along the wire and is finally detected at the point B.

Originally posted by gmonundercover
Electrons 'feel' other electrons because of the negative charge they posses. That's why they don't like 'standing' too close to each other.

They are also fermions and hence subject to the Pauli exclusion principle. Even with no charge at all, that would matter.

Originally posted by buddhasystem
Here's the thing: pressure (as in hydrodynamics) is caused by the medium itself, its constituents. However, a charge can move under the influence of a field, produced externally by sources located at a distance -- sometimes quite large. Your model breaks way too soon when we start looking at electricity. You can't explain the transformer operation, for example.

Except he didn't call it a model, he called it an analogy.

Your point is well taken that the analogy has limitations, (as does any analogy), which I mentioned in my post on page 1. Cosmologists often cite expanding raisin bread as an analogy to the way galaxies are moving away from each other, except you could say that is flawed too because it's the metric expansion of space and not the movement of the galaxies, and you can probably pick more holes in that analogy than you can in the water pressure versus electric voltage analogy, but nonetheless it's a commonly used analogy. Nobody really expects it to be a model, and I'd say the same thing about the water-electricity analogy.

I think the analogies are an attempt to give laypeople who don't understand the ideas some more familiar concepts they can relate to, but I don't think analogies are really intended to be models.
As Dr. Filippenko (one of the cosmologists who uses the raisin bread analogy) said, any analogy breaks down at some point, where it no longer applies. Perhaps even some models also break down where they have a limited scope, they just don't break down as quickly as analogies. For example, the Hubble law is well documented, but even that breaks down at relatively near and relatively far distances...it only works well in the middle, in a vast but still limited range.

This is simply wrong. Temperature control in hot iron (both used for hair, and the pressing iron) is achieved by a thermostat, which is a form of pulse control, i.e. the current is pulsed to keep the temps as the desired level. I thought you'd figure this out because passing a current that big through a variable resistor would cause energy dissipation in that element comparable to the iron itself, or even larger.

You're right about the iron of course, mine uses a pulsed cycling thermostat and I suspect they all would, though I haven't checked that.

One other example that comes to mind is the "dimmer" used to control incandescent lights. The early designs did use variable resistance and were not only inefficient but probably got pretty hot depending on how much dimming one did.

The modern design is pulsed instead, using silicon-controlled rectifiers, but it's pulsed so rapidly you can't tell at normal lighting levels...however sometimes if you turn the dimmer very low, you can see the rapid pulsing or flickering. The typical iron of course has much longer on-off cycles, and you can sometimes even hear the "click" when it cycles if you listen carefully.

Electricity flows because nature tries to achieve electrical neutrality. In an atom, the number of electrons must match the number of protons. You generate electricity by sucking electrons out of some conductive material (like a copper wire). When that wire is connected to an ample source of electrons (like earth), the electrons will flow from earth to replace those missing in the generator. As long as you keep sucking those electrons out, more will keep flowing in. When you connect an electric device or appliance to this chain, electrons will flow though it, doing their work.

The interesting thing is that while we say that electricity flows from a generator, the actual flow is into the generator. Lightning strikes from the ground up, after a channel of ionised air has come down to the ground.

Originally posted by wildespace
The interesting thing is that while we say that electricity flows from a generator, the actual flow is into the generator.

Baloney. If you define the electric current as flow of charge, the generator is simply a part of a closed circuit. One branch has charges moving out, the other same amount of charge moving in. Zero balance.

reply to post by Arbitrageur


I take your point, about analogy not being the same as a model, I guess I'm simply too used to models to accept a surrogate. But you are right -- come think of it, it's not immediately clear what the model of the resistance is... So even the Ohm's law is not quite a model. Well it's an empirical law.

reply to post by buddhasystem

A hot iron is the best example as because altering the temperature control has the actual result of altering the resistance in the circuit.


This is simply wrong. Temperature control in hot iron (both used for hair, and the pressing iron) is achieved by a thermostat, which is a form of pulse control, i.e. the current is pulsed to keep the temps as the desired level. I thought you'd figure this out because passing a current that big through a variable resistor would cause energy dissipation in that element comparable to the iron itself, or even larger.

If a person operates the Thermostat control they are varying resistance is the Iron electrical circuit.

Power = Voltage x Current
and

Voltage = Current x Resistance


If the Voltage source is constant at the outlet source then the Current is descreased or increased by altering the resistance which is controlled by turning the thermostat control one way or other.

Power = V x I and Power expended in a resistive element is heat.

Therefore to increase Heat the either V or I needs to be increased in value.The voltage at the outlet is constant and therefore to increase I then R must be descreased. Or conversly to decrease I then R must be increased.

This phenomenon is explained because Power is also equal to (Current) squared x Resistance. Ill do the maths for you if you want.

Originally posted by AthlonSavage
If a person operates the Thermostat control they are varying resistance is the Iron electrical circuit.

Power = Voltage x Current
and

Voltage = Current x Resistance


If the Voltage source is constant at the outlet source then the Current is descreased or increased by altering the resistance which is controlled by turning the thermostat control one way or other.

Power = V x I and Power expended in a resistive element is heat.

Therefore to increase Heat the either V or I needs to be increased in value.The voltage at the outlet is constant and therefore to increase I then R must be descreased. Or conversly to decrease I then R must be increased.

This phenomenon is explained because Power is also equal to (Current) squared x Resistance. Ill do the maths for you if you want.

For some reason you failed to understand what both Arbitrageur and I described in our respective posts. The resistance of the iron is NOT variable in real-life designs. The thermostat simply regulates how often the heating element is pulsed with full voltage from the mains. Please read Arb's post again, it's pretty good.

reply to post by buddhasystem


Ok i see your point but i m not here to describe the the theory of Thermostats...m here to describe the theory of varying resistance in a electrical circuit. My point is that varying the value of resistance connected across a constant voltage source varies current and therefore varies the heat produced in a resistive element.

I should of used example of a Rheostat which is a device with a dimmer control which varies electrical resistance to vary intensity of light source. I wil check Iron electrical circuits out later to confirm circuit layout (havent got time now).

www.wisegeek.com...

reply to post by AthlonSavage


Great post Athlon, I am an electrician and am constantly refering to electrical knowledge in comparison and understanding to various spiritual concepts etc. I find that everyone generally can understand electricity because it is actually very simple yet few people really have a firm grasp as someone who works with it in their proffession - possibly due to some assumption that electricity is some 'abstract' concept that would be difficult to research or get into. You put this together well. Thanks

reply to post by AthlonSavage


OP- I am not in disagreement with your obviously sound ideas - but, I'm curious about something- This may or may not have significant relevance to your analogous conception of a rainwater tank, which states in part "The analogy of the water fluid system reveals that electric current is flowing/moving in a direction determined by the fall/drop in voltage potential.".

Further on you say:

Voltage is an electrical form of pressure and to understand this concept in the easiest of way is done by
considering its analogy to a fluid system. A simple form of fluid system is found in a rainwater tank. The Pressure inside the tank is greater than the ambient atmospheric pressure surrounding the tank. To release water from the tank into the external environment is controlled by opening a tap on the tank. The flow of water in this manner is analogous to the flow of current. The current flow is commonly referred in everyday terms as electricity.

The first thing that occurred to me while reading through your thoughtful analysis as relates to 'pressure' in the cistern/rainwater tank analogy was the notion of gravity as a source of pressure. Please let us know why you left it out. Thank you.

What's worse is when you look closely at the thing, a lot of these analogies break down. The ping-pong ball one, for instance.

What seems to be going on in a metallic conductor circuit is more like this. The potential source places a field along the circuit. This field propagates at the speed of light determined by the medium and conductor.

That field causes a statistical bias in the random thermal motions of the electrons in the circuit. They will tend to move more one way than the other, but will still be moving with a large random motion vector. They will begin to drift down the circuit. This rate of drift is generally quite slow, in the low meters/second in many cases, for low current circuits it can be much lower.

It's not like you're poking ping-pong balls in a pipe. More like you've got a big tube full of p-d off bees, and a little honey at one end.

edit: I might mention that long ago I used to really cling to some of these analogies as a way to visualize what was going on. While it's a normal process, and at some level it helps (and I STILL do it...) you may find your style of visualizing things getting in the way, as you start having to look at it differently in different circumstances.

I also get really confused by some people's explanations from their internal metaphors when it doesn't jive with mine, thus did I flail for months the first time I had to deal with curl, divergence, and gradient operators, and convolution. I got so tired of "It's like water flowing in a riverbed" "It's like two equations sliding past each other backwards" Feh.

Originally posted by AthlonSavage
I should of used example of a Rheostat which is a device with a dimmer control which varies electrical resistance to vary intensity of light source. I wil check Iron electrical circuits out later to confirm circuit layout (havent got time now).

Or maybe you should read my post and the link to dimmers I provided, which I think covers the dimmer topic more accurately than your link. The modern dimmers are typically pulsed; rheostats were used in old dimmers however, and were inefficient.

reply to post by Arbitrageur


You bet, phase control is da bomb if you can live with the noise. It's way more efficient, rheostats suck.

OTOH, it causes really bad issues with power factor in AC circuits if you have a LOT of stuff doing that...

Originally posted by Arbitrageur

Originally posted by AthlonSavage
I should of used example of a Rheostat which is a device with a dimmer control which varies electrical resistance to vary intensity of light source. I wil check Iron electrical circuits out later to confirm circuit layout (havent got time now).

Or maybe you should read my post and the link to dimmers I provided, which I think covers the dimmer topic more accurately than your link. The modern dimmers are typically pulsed; rheostats were used in old dimmers however, and were inefficient.

edit on 7-11-2012 by Arbitrageur because: clarification

Yes, I agree, to understand modern dimmers one needs to consider the fourth dimension. A dimmer works by applying the same power levels but the levels are restricted in the time domain.

As has been posted before, but ignored, This analogy utterly fails to describe how a transformer functions.

There is always a grave risk if your fundamental understanding is solely based on analogies. If you never rise above the simplistic and limited analogies you will never truly understand.

Electricity and magnetism exist in partnership. No water based analogy will ever explain this complex relationship. In fact, as one delves deeper into understanding electrical energy these water based analogies become blocks to learning.

People are trying to explain their water models and the telling me how electricity works as if their models were proof. This is a dramatic error of logic.

P

Originally posted by pheonix358

Originally posted by Arbitrageur

Originally posted by AthlonSavage
I should of used example of a Rheostat which is a device with a dimmer control which varies electrical resistance to vary intensity of light source. I wil check Iron electrical circuits out later to confirm circuit layout (havent got time now).

Or maybe you should read my post and the link to dimmers I provided, which I think covers the dimmer topic more accurately than your link. The modern dimmers are typically pulsed; rheostats were used in old dimmers however, and were inefficient.

edit on 7-11-2012 by Arbitrageur because: clarification

Yes, I agree, to understand modern dimmers one needs to consider the fourth dimension. A dimmer works by applying the same power levels but the levels are restricted in the time domain.

As has been posted before, but ignored, This analogy utterly fails to describe how a transformer functions.

There is always a grave risk if your fundamental understanding is solely based on analogies. If you never rise above the simplistic and limited analogies you will never truly understand.

I tend to agree.

Moreover, when we look at history, we observe that quite a few analogies were tried to explain things, before the age of the scientific method. Like "phlogiston", five elements (or four, or six), astrology coupled with alchemy etc.

It just doesn't work well.

What beats me is this: the electricity is a fairly simple concept that a child has a fair chance of understanding. Why settle for water cisterns?

reply to post by AthlonSavage

So can you make the Tesla antenna work 100% of the time? This is a problem I cannot overcome, and really want to power the house, and maybe a car.

Originally posted by timmhaines
reply to post by AthlonSavage

 

So can you make the Tesla antenna work 100% of the time? This is a problem I cannot overcome, and really want to power the house, and maybe a car.

What antenna? What problem? And what are you doing to "overcome" same?

reply to post by buddhasystem

to describe how a transformer functions.

Care to explain that one? I'm curious to see if you can.

reply to post by nerbot


Actually I have seen electricity pop a plug out LOL.