Magnetic forces between wires.?

Question

For electric forces, similar charges repel and opposites attract. For magnetic forces, similar poles repel and opposites attract.

How come magnetic forces acting between wires, appear to violate this symmetry? How come it is not a violation (only appears to be a violation)?

Answer 1

The force between current carrying wires is neither the electric force nor the magnetic force but a combination of the two that's called the Lorentz force. If you're familiar with vector notation it's proportional to the cross product of the current density J and the magnetic field B. It is attractive for currents flowing in the same direction it is attractive (I think Chuck is confused on this point).

Answer 2

If you create an electromagnet with a battery and coils of wire around a rod of iron it will have poles and repulsion and attraction like a natural magnet. That is the only example of DC electromagnetism. There are cranes that pick up plates of steel with this method and dozens of magnets suspended on chains controlled by the operator. DC current runs only one direction but AC current runs both directions usually 60 cycles a second.

The most useful action of electromagnetic force between wires is induction and it occurs in AC circuits.

A step down transformer for instance has a primary winding and a secondary winding. If 100VAC was applied to 100 turns of wire in a primary stage, the induction will cross over to the secondary of 10 windings, creating a step down voltage of 10VAC for example.

As for insulated wires next to each other the electromagnetic field can co-exist next to each other without repulsion or if they are of the same phase and voltage they will combine and double the electromagnetic field's strength. The field will rise and collapse 60 times a second for 60 cycle AC.

Check the links below for detailed descriptions.

http://en.wikipedia.org/wiki/Electromagnetic_induction

http://en.wikipedia.org/wiki/Transformer

Answer 3

If the current is going in opposite directions in the wires, the magnetic fields generated are rotating in opposite directions, so the wires would attract when you think they should repel.

Answer 4

If the present is going in opposite guidelines interior the wires, the magnetic fields generated are rotating in opposite guidelines, so the wires could attraction to once you think of they could repel.