# 6: The Magnetic Effect of an Electric Current

- Page ID
- 5451

- 6.1: Introduction
- A bar magnet has some properties that are quite similar to those of an electric dipole. The region of space around a magnet within which it exerts its magic influence is called a magnetic field, and its geometry is rather similar to that of the electric field around an electric dipole – although its nature seems a little different, in that it interacts with iron filings and small bits of iron rather than with scraps of paper or pith-balls.

- 6.2: Definition of the Amp
- If there are two parallel wires each carrying a current in the same direction, the two wires will attract each other with a force that depends on the strength of the current in each, and the distance between the wires.

- 6.4: The Biot-Savart Law
- When we were calculating the electric field in the vicinity of various geometries of charged bodies, we started from Coulomb’s Law, which told us what the field was at a given distance from a point charge. Is there something similar in electromagnetism which tells us how the magnetic field varies with distance from an electric current? Indeed there is, and it is called the Biot-Savart Law.

- 6.7: Helmholtz Coils
- If the separation between two identical parallel plane coils is equal to the radius of one of the coils, the arrangement is known as “Helmholtz coils." They are of particular interest.

- 6.11: Ampère’s Theorem
- Ampère’s Theorem is concerned with the magnetic field around a current-carrying conductor that will enable us to calculate the magnetic field in its vicinity. This is Ampère’s Theorem argues that the line integral of the field H around any closed path is equal to the current enclosed by that path.