A conductor carries 10 Amps, and generates a magnetic field $B$.

  1. How fast does it take for that current to flow from the wire throughout the entire circuit?

  2. And how fast does it take for the magnetic field to be created?


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    $\begingroup$ Take a look at drift velocity for your first question. $\endgroup$ – BMS Mar 26 '14 at 1:46
  • $\begingroup$ @BMS I'm a bit confused can you explain it in a answer? How fast current flows and drift velocity? $\endgroup$ – Pupil Mar 26 '14 at 2:29
  • $\begingroup$ Electromagnetic perturbation flows close to speed of light and this is speed of current despite drift velocity of electrons are low. $\endgroup$ – Schrödinger's Cat Mar 26 '14 at 3:11
  • $\begingroup$ @SachinShekhar Two know that my electronic's current moves near the speed of light and any conducting wire transfers current at that speed is phenomenal. $\endgroup$ – Pupil Mar 26 '14 at 4:26
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    $\begingroup$ Related: physics.stackexchange.com/q/335/2451 , physics.stackexchange.com/q/17741/2451 and links therein. $\endgroup$ – Qmechanic Mar 26 '14 at 19:01

There are 2 ways of looking at the speed of an electric current.

The electrons themselves move quite slowly: of the order of 1.0 m/hour. In other words, if you have a 1m long cable, an electron will take a whole hour to get from one end to the other. For your example, in a copper wire of radius 1 mm carrying a steady current of 10 Amps, the drift velocity is only about 0.024 cm/sec.

However, as soon as an electron starts to move, it affects other electrons around it. Because of this, the current flows out of the other end of the cable almost immediately. As a result, electricity travels down the wire at about $2/3$ of the speed of light.

Magnetic fields, on the other hand, travel through space at the same speed as electric fields: the speed of light. I don't know how fast they travel through magnetic materials, but it will be somewhat slower than $c$.

  • $\begingroup$ Actually, let me elaborate on the second point. The electron moves because you apply a voltage to the wire, which is nothing else but creating an electric field in the wire. The force due to this electric field will be felt by all electrons simultaneousely, which is why the all get in motion right away and you don't need to wait a notable time e.g. between flicking the light switch and the light actually becoming bright. $\endgroup$ – Neuneck Mar 26 '14 at 7:31
  • $\begingroup$ The electrons themselves move quite slowly Quantum mechanicaly, they move really fast (Fermi speed). $\endgroup$ – jinawee Mar 26 '14 at 19:28

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