- Magnetic Circuits Definition: A magnetic circuit is defined as the path in space through which magnetic flux passes.
- Flux Path in Solenoids: Flux lines in an iron-cored solenoid travel from the N pole, through the air, to the S pole, and back through the iron core.
- Composite Magnetic Circuit: A composite magnetic circuit has flux lines passing through both air and iron, creating a non-uniform field outside the core.
- Uniform Magnetic Field: Within the iron core, flux lines are evenly spaced, resulting in a uniform magnetic field.
- Enclosed Magnetic Circuit: Using a toroid core creates an enclosed magnetic circuit with a uniform magnetic field, eliminating flux lines passing through the air.
A magnetic circuit is a closed path that magnetic flux follows, the magnetic analogue of an electric circuit. An iron-cored solenoid carrying DC sets up flux that leaves the N pole, crosses air to the S pole, then returns in the iron. A path that uses both air and iron is a composite magnetic circuit. Inside the iron the lines are much more evenly spaced than they are in air.
That even spacing means the magnetic field in the iron is nearly uniform. In the air around a straight core the lines spread, so the field is not uniform. Design work is easier if the field stays in the iron. A toroid of uniform section does that: almost none of the flux has to cross air. The circuit is then enclosed and the field in the core is nearly uniform. A little leakage still exists.
