1

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?

Qmechanic
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Pupil
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1 Answers1

4

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 $c$.

hdhondt
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