Magnetic Properties of Current

All magnetism actually is the result of charged particles in motion (electrical currents). Even an iron atom is made up of charged particles in motion (electrons). There are many special magnets which are made up of current-carrying wires (electromagnets). One example is a solenoid. The magnetic field runs down the inside axis of a helical coil of wire-- this can be useful in many ways including the construction of switches. A bar magnet positioned inside the solenoid can be pulled or pushed when the electrical current is suddenly turned on.

If a helical coil is made more planar, its axial field moves outside the coil so that it resembles the field of a bar magnet or compass needle. This kind of electromagnet is called an armature. When placed in the external field of a horseshoe magnet, an armature can be rotated by a torque that is proportional to the current flowing in the coil-- this is the basis for electrical meters (galvanometer, ammeter, voltmeter) and for D.C. motors.

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