How fast is Electricity?

Question

Electricity appears to bring instant power. But it must take a measurable amount of time to go from ON to Off.
If you had a switch and a light millions of miles apart but could see them both at the same time, would it still appear instant?
Would the answer be the same even if the link between them was a perfect conductor of electricity?

Answer 1

The speed of the propagation of the electric field within a wire is limited by the speed of light. Information cannot travel faster than light, so if you switched on a light bulb millions of miles away it would take a very noticeable lag before you see the light come on.
First the electricity must travel down the wire at a speed no faster than c, then the light emitted by the bulb must return at c.

It is important to note that although the influence of the electric field propagates at the speed of light, the electrons making up the electric current do not travel this fast themselves since they have mass. The individual electrons in the current carrying wire travel much more slowly. The electrons that go "into" one end of the wire are not the same electrons that "come out" of the other end.

Answer 2

The answer is that it varies, depending on the nature of the electrical circuit.
The rate at which electrical signals of any kind travel along a wire or cable depends on the associated inductance, capacitance and resistance. Also, in general, high frequency signals will tend to be attenuated (reduced) more rapidly than low frequency signals as the further they travel.
The theoretical maximum velocity is the same as the speed of light (about 186,000 miles per second, or 300,000,000 metres per second if you prefer). If you consider, say, TV signals travelling along a co-axial cable then there is an associated 'velocity factor' which, from memory, is somewhere in the region of 85% for semi-air-spaced cable or 67% for cable with a solid dielectric. (I'm referring to the insulation between the inner and outer conductors.) In other words, the TV signals in the cable travel at 85% (or 67%) of the speed of light. (On the other hand, the TV signals travel at the speed of light between the transmitting and receiving aerials because that's when they are in the form of electromagnetic radiation - the same as light but with a much longer wavelength.)
Maybe you were thinking of switching on something like a light bulb in your house but the general principle is the same - except, of course, that the light itself doesn't turn on instantaneously. That's another can of worms since it would depend what sort of light bulb it was.
Hope this helps !

Answer 3

i thought it moved at the speed of light but maybe not......i found this explaination.........Within all metals there is a substance which can move. This stuff has several different names: the Sea of Charge, or the Electron Sea, or the Electron Gas, or "charge." We often call it "electricity." Calling it "electricity" can be misleading because charge is not energy, yet many people think that electrical energy is the "electricity." It can be misleading because the Sea of Charge exists within in all metal objects, all the time, even when the metal has not been made into a wire and is not part of an electric device. If the Electron Sea is "electricity," then we must say that all metals are full of electricity. Better to call it by the name "charge-sea," and avoid the misleading word "electricity".

During an electric current, the wire stays still and the sea of charge flows along through it. When the flashlight switch is turned off and the lightbulb goes dark, the charge-sea stops moving forward. Even though it stops moving, the charge-sea is still inside of that wire. If the flashlight is again turned on and two light bulbs are connected in parallel instead of one, the electric current will have twice as large a value, and twice as much light will be created. And most important, the charge-sea of the battery's wires will flow twice as fast. In other words, THE SPEED OF THE CHARGES IS PROPORTIONAL TO THE VALUE OF ELECTRIC CURRENT; small current means low-speed charge flow, large current means high speed. Zero current means the charges have stopped. Note however that an electric current does not have just one speed. Charges speed up when they flow into a thinner wire. The high current in the lightbulb of a big flash-lantern will be much faster than the same current in the conductors in the lantern. Even though an electric current is a very slow flow of charges, we can't know the actual speed of flow unless first we know the *value* (the amperes) of the current in the wires.


If a thin wire is connected in a circuit end to end with a thick wire, it turns out that the charges in the thin wire move faster. This makes sense, it works just like water in rivers. If a huge wide river moves into a narrow channel, the water speeds up. When the channel opens out again downstream, the river slows down again. The flow in a very thin wire will be tend to be fast, even if the value of current is fairly low. This means that we can't know the speed of the flowing charge-sea unless we know how thick the wires are.


If a copper wire is connected into a series circuit with an aluminum wire of the same diameter, the charges in the copper will flow slower. This occurs because there is one movable charge per each atom in the metals, but there are more atoms packed into the copper than into the aluminum, so there is more charge in each bit of copper. When the charge-sea flows into the copper, it gets packed together and slows down. When it flows out into the aluminum, it spreads out a bit and speeds up. This means that we cannot know how fast the charges flow unless we know how dense the charge-sea is within the metal.



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

Answer 4

The best conductor of electricity is gold. There are however ultra low temperature ways of transmitting electric power at faster speeds. You could probably find out more on the speed of electric transmission through cables by going to your electricity supplier's website and see if they have a 'contact us' and ask your question there.

As a basic rule of thumb, electricity in air, such as a lightning strike, probably moves at speeds close to that of light. You'll need to ask Ben Franklin about this, because as far as I know, he's the last guy who tried to find out about electricity by flying a kit in an electric storm. Mad or what?

Answer 5

It depends on what medium the light is travelling through. Waves and a more formal version of Snell's Law comes into play if the light travels trough different mediums eg from a more dense medium to a less dense medium.

Answer 6

Electricity actually moves through copper wire at 0.7 times the speed of light. That's the standard you use when calculating delay

Answer 7

Light energy does move at different speeds in different mediums, so the kid has a point.

Answer 8

the speed of light , that's how fast

Answer 9

speed of light 186000 m/s or 3.0x10^8m/s

Answer 10

so, a million miles would be about 5.38 sec.....