Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Consider two parallel wires of finite radius. When a current is applied to one of the wire for a short period of time, what is the current induced in the other wire?

Applying Maxwell's equations, it seems that there is a change in magnetic field perpendicular to the second wire, and as a result, the induced current has a nontrivial distribution which averages somewhat to zero. Is this correct? Intuitively, I had instead expected a simpler result similar to the case of two coils of wires placed side by side.

share|cite|improve this question
up vote 1 down vote accepted

I think there is a non-zero induced current.

1) During the rise (and fall) of the current pulse in wire 1, a changing, azimuthal, magnetic field is generated (calculable by Ampere's law).

2) Per Maxwell, that changing B-field induces an electric field parallel to the wires, which:

3) causes a current to flow in wire 2 (assuming a wire resistivity $\rho$ and applying Ohm's law).

Thus, if one applies a short pulse of current to wire 1, you'd see two even shorter pulses in wire 2, one positive and one negative, aligned with the rise and fall of the wire 1 current.

There is some variation in E with respect to the radial dimension, which would complicate an exact solution, but the variation is small (and it doesn't result in cancellation).

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.