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what is the speed of electricity ???
montanajoe
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Its close enough... you won't be able to dodge it, if thats what you're worried about.
quote:The speed of electric current
Since nothing visibly moves when the charge-sea flows, we cannot measure the speed of its flow by eye. Instead we do it by making some assumptions and doing a calculation. Let's say we have an electric current in normal lamp cord connected to bright light bulb. The electric current works out to be a flow of approximatly 3 inches per hour. Very slow!
Here's how I worked out that value. I know:
Bulb power: about 100 watts, about 100V at 1A
Value for electric current: I = 1 ampere
Wire diameter: D = 2/10 cm, radius R=.1cm
Mobile electrons per cc (for copper, if 1 per atom): Q = 8.5*10^+22
Charge per electron: e = 1.6*10^-19
The equation:
cm/sec = ________I_______ = .0023 cm/sec = 8.4 cm/hour
Q * e * R^2 * pi
This is for DC. Chris R. points out that for a particular value of frequency of AC, the "skin effect" can cause the flow of charges in the center of a wire to be reduced while the current on the surface becomes stronger. There are fewer charges flowing, and hence they must flow faster. ("Skin Effect" is stronger at high frequencies and with thick wires. The effect can USUALLY be ignored in thin wires at 60Hz power-line frequencies.)
The size of the wiggle
And about AC... how far do the electrons move as they vibrate back and forth? Well, we know that a one-amp current in 1mm wire is moving at 8.4cm per hour, so in one second it moves:
8.4cm / 3600sec = .00233 cm per second
And in 1/60 of a second it will travel back and forth by
.00233cm/sec * (1/60) = .0000389cm, or around .00002"
This simple calculation is for a square wave. For a sine wave we'd integrate the velocity to determine the width of electron travel.
So for a typical AC current in a typical lamp cord, the electrons don't actually "flow," instead they vibrate back and forth by about a hundred-thousandth of an inch.
The width of one Coulomb
On thinking along these lines I notice something interesting: in copper, one coulomb of movable electrons has a certain size! There are about 13,000 coulombs of free electrons per cubic centimeter of copper.
8.5*10^+22 elect/cc * 1.6*10^-19 coul./elect = 13600 Coul./cc
Therefore one coulomb would form a cube approximately 0.4mm across...
1/(13600cc^(1/3)) = 0.042 cm
HA! A coulomb in copper is about the size of a grain of sand! We can now discuss electric currents within wires as if they were cc-per-second fluid-flows inside of small hoses. If an Ampere is one coulomb per second, we're REALLY saying that an Ampere is "one saltgrain-sized blob, moving each second, squeezing itself into whatever sized wire." So, for the usual sizes of wires used in electric circuitry, if we deliver one salt-grain per second (one amp,) that's a very slow flow. The tiny saltgrains are going by: bip, bip, bip, once per second.. In 16-gauge wire the saltgrain blobs would be morphed to fill the cross-section, so they would resemble very thin stacked pancakes. In 30-gauge wire the saltgrains would be almost undistorted, and so the charges would move at about 0.4 mm/sec during a 1-amp current.
One thing's not certain in the above calculations: the charge density for copper. My above value for Q assumes that each copper atom donates a single movable electron. The email from the person below points out that this might not be true. For example, if only one in ten conduction electrons are movable, while the rest are "compensated" and frozen, then the speed of the charge flow will be ten times greater than 8.4cm/hour.
One final point. Electrons in metals do not hold still. They wiggle around constantly even when there is zero electric current. However, this movement is not really a flow, it is more like a vibration, or like a high-speed wandering movement. How should we picture this? Well, remember that we can speak of moving wind and flowing water as if they had a genuine velocity... yet a similar type of rapid wandering motion is found in the atoms of all normal liquids and gases. Even when the wind is less than one MPH, the air molecules are zooming around at hundreds of MPH. Even when there is no wind at all, the air molecules still wiggle around at the same high speeds. We usually ignore this when discussing wind, and instead take the average velocity of all molecules in a certain small volume. We call it "thermal vibration," and we see the fast movements as a separate issue. Therefore we should do the same with circuitry: the electric current is akin to wind, while the high speed wandering motions of individual electrons is akin to thermal vibrations of the air. In the above article I concentrate on the slow "electron wind" which is measured by electric current meters, and I ignore the electrons' high speed "thermal vibration."
fast.
Freaky fast.
you know how many amps you're drawing. you know an amp is "so many electrons per second".
then think of a copper wire like a hose, and electrons are like water going through the hose. with a fat hose, it's wider, so the electrons don't have to move fast to put out the same amount. with a skinny hose, they do have to move faster to put out the same amount.
electrons transfer between copper atoms, so you get 1 electron per copper atom. figure out the density of copper atoms in the wire, that's like a cross-section of water in a hose. simply plug in the numbers.
we did that in physics class once. I forgot the numbers, but it was about slow enough to watch it crawl along the wire. not even a foot per second.
lightning would be different because there is a huge amount of amperage, and it's crowded on the least air/water molecules possible. you would use the same calculations just different numbers. you can guess it's "lightning fast".
Unlike light where a photon produced in one place actually transits different media at different speeds and arrives somewhere else, an electron doesn't quite do that as a matter of practicality.
Consider the conductor a garden hose filled with water. In theory if you push an ounce of water in one end an ounce of water will exit the other rather quickly... But it's not the same water you push into the opposite end of the hose unless you're patient and it doesn't happen at the speed of light. Electrons are surprisingly similar in behavior.[:)]
the speed of electricity through a copper wire is easy.
you know how many amps you're drawing. you know an amp is "so many electrons per second".
then think of a copper wire like a hose, and electrons are like water going through the hose. with a fat hose, it's wider, so the electrons don't have to move fast to put out the same amount. with a skinny hose, they do have to move faster to put out the same amount.
electrons transfer between copper atoms, so you get 1 electron per copper atom. figure out the density of copper atoms in the wire, that's like a cross-section of water in a hose. simply plug in the numbers.
we did that in physics class once. I forgot the numbers, but it was about slow enough to watch it crawl along the wire. not even a foot per second.
lightning would be different because there is a huge amount of amperage, and it's crowded on the least air/water molecules possible. you would use the same calculations just different numbers. you can guess it's "lightning fast".
The coulomb (symbol: C) is the SI derived unit of electric charge. It is defined as the charge transported by a steady current of one ampere in one second:
One coulomb is also the amount of excess charge on the positive side of a capacitance of one farad charged to a potential difference of one volt:
Staying below that, will keep you safe.
In non-technical terms you might say the following:
Unlike light where a photon produced in one place actually transits different media at different speeds and arrives somewhere else, an electron doesn't quite do that as a matter of practicality.
Consider the conductor a garden hose filled with water. In theory if you push an ounce of water in one end an ounce of water will exit the other rather quickly... But it's not the same water you push into the opposite end of the hose unless you're patient and it doesn't happen at the speed of light. Electrons are surprisingly similar in behavior.[:)]
That is a very good way to describe it.
So you don't use electricity - you just rent it.
....it is actually a different speed in different materials.
DING!DING!DING!
Depends
You answered the wrong question. You answered "What does oral sex taste like in a nursing home", not how fast is electricity.![:D]
How fast does a road go? It doesn't. It is always at the begining all the way to the end, all the time.
So it does'nt travel. What if you have a dead wire 100 miles long and electrify it? Is the power at the other end faster than a fiber optic cable?
quote:Originally posted by duckhunter
Depends
You answered the wrong question. You answered "What does oral sex taste like in a nursing home", not how fast is electricity.![:D]
LOL,[:D][:D][:D]
quote:Originally posted by bigdaddyjunior
How fast does a road go? It doesn't. It is always at the begining all the way to the end, all the time.
So it does'nt travel. What if you have a dead wire 100 miles long and electrify it? Is the power at the other end faster than a fiber optic cable?
One of my text books when I was schooling for my card said they can not accurately measure it, but that if you had a wire from San Francisco to New York and put one electron in at one end there would be one electron pushed out the other end instantly.
quote:Originally posted by buschmaster
the speed of electricity through a copper wire is easy.
you know how many amps you're drawing. you know an amp is "so many electrons per second".
then think of a copper wire like a hose, and electrons are like water going through the hose. with a fat hose, it's wider, so the electrons don't have to move fast to put out the same amount. with a skinny hose, they do have to move faster to put out the same amount.
electrons transfer between copper atoms, so you get 1 electron per copper atom. figure out the density of copper atoms in the wire, that's like a cross-section of water in a hose. simply plug in the numbers.
we did that in physics class once. I forgot the numbers, but it was about slow enough to watch it crawl along the wire. not even a foot per second.
lightning would be different because there is a huge amount of amperage, and it's crowded on the least air/water molecules possible. you would use the same calculations just different numbers. you can guess it's "lightning fast".
The coulomb (symbol: C) is the SI derived unit of electric charge. It is defined as the charge transported by a steady current of one ampere in one second:
One coulomb is also the amount of excess charge on the positive side of a capacitance of one farad charged to a potential difference of one volt:yes, and, there are a defined amount of electrons in that amount of charge.
quote:Originally posted by bigdaddyjunior
How fast does a road go? It doesn't. It is always at the begining all the way to the end, all the time."Behold this gateway, dwarf!" I continued. "It has two faces. Two paths meet here; no one has yet followed either to its end. This long lane stretches back for an eternity. And the long lane out there, that is another eternity. They contradict each other, these paths; they offend each other face to face; and it is here at the gateway that they come together. The name of the gateway is inscribed above: 'Moment'. But whoever would follow one of them, on and on, farther and farther- do you believe, dwarf, that these paths contradict each other eternally?"
"All that is straight lies," the dwarf murmured contemptuously. "All truth is crooked; time itself is a circle."
"Behold," I continued, "this moment! From this gateway, Moment, a long, eternal lane leads backward: behind us lies an eternity. Must not whatever can walk have walked on this lane before? Must not whatever can happen have happened, have been done, have passed by before? And if everything has been there before- what do you think, dwarf, of this moment? Must not this gateway too have been there before? And are not all things knotted together so firmly that this moment draws after it all that is to come? Therefore- itself too? For whatever can walk- in this long lane out there too, it must walk once more.
"And this slow spider, which crawls in the moonlight, and this moonlight itself, and I and you in the gateway, whispering together, whispering of eternal things- must not all of us have been there before? And return and walk in that other lane, out there, before us, in this long dreadful lane- must we not eternally return?"
The tough question is does the electricity (electrons) travel through the wire or as a field around the wire?
they travel through the wire. each electron is transmitted from atom to atom. a wire with electricity running through it does have a field of electric potential around it though, that's how it's possible for a spark to jump. the more voltage, the farther a spark can jump, as you know. it also creates a magnetic field perpendicular to the current as if wrapped around the wire. the direction of the magnetic field vector uses "the rule of thumb": when your thumb points along the direction of current, your fingers go in the direction of the the magnetic field as it circles around the wire.
nothing is transmitted along the wire as a field around the wire.
however, you can use that phenomenon to transfer electric power between two wires. since a wire has current running through it and a magnetic field around it, what happens when you wrap that wire around another one? the magnetic field wrapped around adds up to an electric potential going through the middle of the coil in one direction- just like a wire. and there happens to be a wire there, so it picks up the electric potential and creates a current. that's called inductance.
so then what you can do is, instead of a wire, use a bar of metal, and wrap another wire around the bar a little farther away. a different number of wrappings gives a different ratio of current and volts in the secondary wire but still the same power throughput. that's called a transformer. usually instead of a bar, a round or square piece of metal with a hole in the middle is used and wire wrapped on either side, because electric current keeps flowing around the metal instead of simply going from one wrapping, through the bar, to the other wrapping.
when too much electric current (that is, power) flows around the circle (or square), the covalent bonds of the atoms holding the metal together can't hold any longer and it blows up.
Someone was talking about AC and DC voltage--in those cases the electrons don't really have a net motion, they vibrate back and forth. This is why I think what you're getting at, again, is the speed of electromagnetic waves, the net effect of electricity.
quote:Originally posted by He Dog
The tough question is does the electricity (electrons) travel through the wire or as a field around the wire?
they travel through the wire. each electron is transmitted from atom to atom. a wire with electricity running through it does have a field of electric potential around it though, that's how it's possible for a spark to jump. the more voltage, the farther a spark can jump, as you know. it also creates a magnetic field perpendicular to the current as if wrapped around the wire. the direction of the magnetic field vector uses "the rule of thumb": when your thumb points along the direction of current, your fingers go in the direction of the the magnetic field as it circles around the wire.
nothing is transmitted along the wire as a field around the wire.
however, you can use that phenomenon to transfer electric power between two wires. since a wire has current running through it and a magnetic field around it, what happens when you wrap that wire around another one? the magnetic field wrapped around adds up to an electric potential going through the middle of the coil in one direction- just like a wire. and there happens to be a wire there, so it picks up the electric potential and creates a current. that's called inductance.
so then what you can do is, instead of a wire, use a bar of metal, and wrap another wire around the bar a little farther away. a different number of wrappings gives a different ratio of current and volts in the secondary wire but still the same power throughput. that's called a transformer. usually instead of a bar, a round or square piece of metal with a hole in the middle is used and wire wrapped on either side, because electric current keeps flowing around the metal instead of simply going from one wrapping, through the bar, to the other wrapping.
when too much electric current (that is, power) flows around the circle (or square), the covalent bonds of the atoms holding the metal together can't hold any longer and it blows up.
To my mind, this does not differ significantly from magic.
And fiery auto crashes
Some will die in hot pursuit
While sifting through my ashes
Some will fall in love with life
And drink it from a fountain
That is pouring like an avalanche
Coming down the mountain
thats the key. there IS a positive or fwd flow of those little electric whatchamacallits due to loss at the device being powered. so even though the effect of throwing a switch is instantaneous, the actual flow of the watchmacallits is not.
they flow at 120 ft/sec which equals 81.8182 mph, +/- 0.001 (i did the calculation in my head)[;)]