Educator

Magnetic Field Produced by Currents

• A long, straight wire carrying a current I, produces a magnetic field, whose value at a distance r from the wire, is (mu_0) I / 2(pi)r, where (mu_0) is called the permeability of free space, and in SI units, its value is 4(pi)x10^-7 T.m/A. The direction of the magnetic field is determined by the right hand rule: place the thumb of your right hand along the direction of the current, and the four fingers will then be in the direction of the field.
• Two parallel wires carrying currents exert forces on each other. If the currents are parallel, the force will be attractive, and if they are anti-parallel the force will be repulsive.