Magnetic Effects of Current

Every magnetic field discussed so far came from a permanent bar magnet. Oersted's discovery (next section) showed that a steady electric current is itself a source of magnetic field, with its own field-line pattern around straight wires and coils, describable with two simple right-hand rules before the Biot-Savart and Ampere's-law formulas of §3.8-3.9 make it quantitative. This is the pivot point of the whole unit: everything before this section treats magnetism as a property of permanent magnets; everything from here on shows that ordinary elec …