summary
● The word magnet is derived from the name of magnetite, a mineral that is a natural magnet.
● Rubbing a piece of soft iron with another magnet can create a magnet.
● Current flowing in a coil of wire creates an electromagnet.
● Horseshoe, bar, rectangular, and ring are the most common shapes of magnets.
● Unlike poles attract and like poles repel.
● One theory of magnetism is based on the spin of electrons as they orbit around an atom.
● Another theory of magnetism is based on the alignment of domains.
● Flux lines are invisible lines of force surrounding a magnet.
● Flux lines form the smallest loop possible.
● Permeability is the ability of a material to accept magnetic lines of force.
● A magnetic field surrounds a wire when current flows through it.
● The direction of the flux lines around a wire can be determined by grasping the wire with the left hand, with the thumb pointing in the direction of current flow. The fingers then point in the direction of the flux lines.
● If two current-carrying wires are placed next to each other, with current flowing in the same direction, their magnetic fields combine.
● The strength of an electromagnet is directly proportional to the number of turns in the coil and the amount of current flowing through the coil.
● The polarity of an electromagnet is determined by grasping the coil with the left hand with the fingers in the direction of current flow. The thumb then points toward the north pole.
● Retentivity is the ability of a material to retain a magnetic field.
● Electromagnetic induction occurs when a conductor passes through a magnetic field.
● Faraday’s law: Induced voltage is directly proportional to the rate at which the conductor cuts the magnetic lines of force.
● The left-hand rule for generators can be used to determine the direction of induced voltage.
● AC and DC generators convert mechanical energy into electrical energy.
● A relay is an electromechanical switch.
● Electromagnetic principles are applied in the design and manufacture of doorbells, solenoids, phonograph pickups, loudspeakers and magnetic recordings.
● DC motors and meters use the same principles.
● Electron beams can be deflected by an electromagnetic field to produce images on television, radar and oscilloscope screens.