electricity travelling in a circuit?

Question

Is the classic description of electricity travelling in a circuit based on electrons whizzing around at the speed of light? If so, regardless of the low resistance of the cables, why don't the wires in my walls get incredibly hot? In a lightbulb the high resistance of the filament "slows down" the electrons causing them to give off energy in the form of heat and light. This doesn't make sense to me. If electrons are "bumping into" tungsten in the lightbulb they must also be "bumping into" copper in the cables. Due to the numbers of collisions and the speeds involved, surely huge heat should be generated? Does anything actually "move" around a circuit? Let's call an electron "John". Does John move from point A to point B which is further along the circuit, then to point C etc. etc.
If not, what exactly is moving through the cables? Or is the classical picture just inadequate to describe the transfer mechanism(s).

Answer 1

The fields travel through the wires at close to the speed of light. The electrons experience what's called a drift velocity which is just a few milimeters per second. There's no way electrons are flying at the speed of light since that would involve a particle accelerator that takes up acres to get to that energy....
Here's a good description

http://en.wikipedia.org/wiki/Current_(electricity)

Answer 2

The question is not clear - further than what? This question will only arise due to the way the circuit is drawn in a circuit diagram . If a wire is marginally longer in a circuit it will have little or no effect on the flow of current as the wires are assumed theoretically to have zero resistance - in practice the wires too will have insignificant resistance compared to the component in the circuit. If we are comparing the parallel circuit with a series one then it is the combined resistance that has to be considered not the length of the wires. The parallel circuit divides the current as you suggest making it easier for it to flow so the resistance is lower. A series circuit gives a larger resistance to the flow -so the current is reduced - distance travelled has no effect . Good luck with your PGCE course - make sure you join the NASUWT ( the best union) before you go into schools.

Answer 3

Current flowing through cables does generate heat but the amount is small due to the diameter of the cable and is dissipated by the length of the cable. A wire will over heat if more current is passed through it than it is capable of taking and this is also how a fuse works. It is a piece of fine wire which overheats and melts if too much current passes through it
You will also find that if you connect a piece of equipment which draws a large current such as an electric heater using a coiled up extension lead the lead will become hot.

Answer 4

There are a lot of issues with electricity.
Firstly,out of interest, they don't travel at the speed of light. They hop between the conduction bands of the atoms/molecules.
Secondly,out of interest, the electrons actually flow the opposite way to the traditional V=IR calculations.

The filament is very fine so the electrons are forced to travel over many fewer molecules (it reaches an equilibrium of resistance as the kenetic energy of the molecules vibrating impedes the movement of electrons between atoms).The kenetic energy is released as heat and light. It took a lot of practical experimentation to determine the best material/coatings for those filaments.

The copper wire described, have many more atoms to transfer the electrons over, and have much more ability to conduct heat (kenetic energy) away from the atoms and liberate it into the air.

It is interesting to note that the current (measure of amount of electrons passing through the material) is the main factor for heat generation and not the voltage (the energy potential between the points). If you have a wire that will burn out at 3A. It will burn out at 3A at 10V,24V,50V,100V etc.

This is very much simplified - hope it helps.

Answer 5

It's the amount of current per mm² that causes the heat. Tungsten filaments are very small in cross section compared to the wire leading to the bulb.

Also the electrons are not 'whizzing around' at the speed of light or anywhere near it.

Answer 6

Electorns in a circuit travel as a wave in the metal. It's fast, hundreds of thousands of miles and hour, but no where near the speed of light.The electrons heat the circuit as they move around, that's why a lot of equipment has to be cooled.

Answer 7

A good analogy is a long tube filled with marbles lined up end to end. If you push another marble in one end, a marble almost instantaneously pops out of the other end. It isn't that the marbles are traveling that fast, in fact, they are traveling rather slowly, but the effect is almost instant.
Now consider how much heat the friction will cause if we start forcing more and more marbles into a tube that's too narrow for the free movement of the marbles.

Answer 8

Hi. The electrons do NOT travel at the speed of light. The voltage does (or comes close). Consider a garden hose. Turn on the spigot and the PRESSURE goes up immediately even though the water is not moving.

Answer 9

The tungsten impedes the flow of electrons a lot more than the copper does..

Think of pushing a mouthful of water (as fast as you can) through an open garden hose and then compare that to pushing it through a straw.

Answer 10

the size of the cable in your walls is more than capable of carrying a lighting circuit current without overheating.

the filament in your lightbulb is too small for the current flowing through it but doesn't burn out as it's in a vacuum sealed globe so can't do so but boy does itr glow brightly.