MAGNETISM, ELECTROMAGNETISM AND ELECTRICITY

Magnetite

Oxide of iron (Fe3O4) discovered around 1000 BC near Magnesia with natural magnetic properties.

Lodestone

Naturally occurring magnet that aligns to Earth's magnetic field and was used as an early compass.

Magnetism

Fundamental property of some matter, involving polarization, difficult to detect or measure.

Magnet

Material that produces a magnetic field.

Bipolar or Dipolar magnets

Magnets with two poles.

Poles

Ends of a magnet where the magnetic field is strongest.

Magnetic lines of induction

Imaginary lines representing a magnetic field.

Law of magnetic poles

Property stating every magnet has a north and south pole, like poles repel, unlike poles attract.

Maxwell’s field theory of electromagnetism

Magnetic force behaves like electrostatic and gravitational forces, inversely proportional to square of distance.

Domain theory of magnetism

Theory stating 10¹⁵ atoms make up a single dipole, and dipoles align or cancel depending on conditions.

Magnetic domain

Region in a material where atomic magnetic dipoles are aligned.

Lines of force (Lines of flux)

Lines of magnetic field surrounding a magnet in three dimensions.

Outside: North to South; Inside: South to North

Magnetic field direction outside and inside a magnet.

Magnetic field line property

Magnetic field lines never intersect and may be parallel in some descriptions.

Weber (Wb)

SI unit of magnetic flux equal to 10⁸ lines of flux.

Tesla (T)

Unit of magnetic flux density equal to 10,000 gauss.

Magnetic flux density

Magnetic flux density measured in tesla (T) or gauss (G).

Electron spin

Property caused by electron spin creating a magnetic field.

Magnetic moment

Magnetic field created by a spinning proton in a hydrogen nucleus.

Nuclear magnetic dipole

Basis of Magnetic Resonance Imaging (MRI).

Magnetic field continuity

Magnetic field lines always form closed loops.

Magnetic dipole

Small magnet created by electron orbital motion.

Magnetic permeability

Ability of a material to attract magnetic field lines.

Magnetic retentivity

Ability of a material to remain magnetized.

Inversely proportional

Relationship between permeability and retentivity.

Naturally occurring magnets

Magnets found in nature such as Earth and lodestone.

Artificial permanent magnets

Magnets made in various shapes from iron, e.g., bar or horseshoe magnets.

Electromagnets

Magnets formed by wire around an iron core carrying current.

Permeability

Ease with which a material can be magnetized.

Retentivity

Ability of a material to stay magnetized.

Ferromagnetic

Magnetic classification with high permeability.

Paramagnetic

Magnetic classification with slight attraction to magnets.

Diamagnetic

Magnetic classification repelling magnetic fields.

Nonmagnetic

Materials not affected by magnetic fields.

ALNICO

Strong ferromagnetic alloy magnet made from aluminum, nickel, cobalt.

Rare earth magnets

Extremely strong magnets developed from rare earth materials.

Magnetic divisibility

Breaking a magnet results in two smaller magnets, each with both poles.

Magnetic induction

Process of making a material magnetic by placing it in a magnetic field.

Magnetic line density rule

Density of magnetic lines proportional to field strength.

Magnetic shielding

Use of ferromagnetic material to reduce MRI fringe fields.

Inverse square law of magnetism

Principle that magnetic force increases fourfold if distance is halved.

50 μT at equator, 100 μT at poles

Earth's magnetic field behavior at the poles and equator.

Northern Canada

Location of Earth's magnetic north pole.

Antarctica

Location of Earth's magnetic south pole.

First law of magnetism

Law stating like poles repel, unlike poles attract.

Second law of magnetism

Law stating magnetic force follows inverse square law with distance.

Third law of magnetism

Law stating every magnet has a north and south pole.

Pre-19th century view of electricity and magnetism

Scientific view before the 19th century that electricity and magnetism were unrelated effects.

Voltaic pile

Stack of zinc and copper plates used to produce electric current, precursor to modern battery.

Cell

Individual zinc–copper sandwich in a Voltaic pile.

Carbon rod

Positive electrode in a modern dry cell.

Zinc cylinder can

Negative electrode container in a modern dry cell.

Source of electric potential

Any device converting other forms of energy into electric energy.

Hans Oersted

Danish physicist who discovered the link between electricity and magnetism in 1820.

Oersted's discovery

Effect observed when current through a wire deflects a compass needle.

Electromagnetic induction

Process where an electric current is induced in a circuit by a changing magnetic field.

Michael Faraday

Scientist who described the first law of electromagnetic induction.

Faraday’s law of electromagnetic induction

Faraday’s finding that a changing magnetic field induces current in a coil.

Oersted’s experiment

Experiment showing that electricity generates magnetic fields.

Mutual induction

Production of current in a neighboring circuit.

High-voltage transformer

Example of mutual induction in x-ray equipment.

Self-induction

Production of current within a coil that opposes the change in current.

Autotransformer

Example of self-induction device in x-ray equipment.

Charge at rest

State of a charge that produces no magnetic field.

Circular magnetic field lines

Magnetic field created around a conductor carrying current.

Magnetic field of a wire loop

Magnetic field lines forming concentric circles around each section of a loop.

Center of the loop

Area where all field lines overlap inside a loop, producing strongest field.

Solenoid

Stacking multiple loops to increase magnetic field intensity.

Solenoid field concentration

Concentration of magnetic field through the center of a coil.

Electromagnet

Device formed by wrapping a coil around a ferromagnetic core to intensify the magnetic field.

Electromagnet core field confinement

Confinement of magnetic field lines inside an electromagnet core, escaping only at ends.

Adjustable magnetic field

Advantage of an electromagnet where field strength can be varied by adjusting current.

Faraday’s principle of induction

Principle that only a changing magnetic field can induce current; a constant field cannot.

Radio antenna induction

Example where oscillating magnetic fields induce electron motion to create a signal.

Electric motor

Device where electric current produces mechanical motion.

Electric generator

Device where mechanical motion produces electric current.

Induction motor

Motor type used to rotate the anode in x-ray tubes.

Stators

Stationary electromagnets in an induction motor.

Rotor

Rotating component in an induction motor made of copper and iron bars.

Rotating magnetic field in induction motor

Motor principle where stator windings are energized sequentially to rotate a magnetic field.

Transformer

Device that uses interacting magnetic fields from changing currents to alter voltage and current.

Primary coil

Coil in a transformer receiving the input current.

Secondary coil

Coil in a transformer delivering the output current.

Alternating current (AC) only

Condition for transformer operation.

Transformer law

Law describing voltage change proportional to turns ratio in a transformer.

Step-up transformer

Relationship between turns ratio and voltage increase.

Step-down transformer

Relationship between turns ratio and voltage decrease.

Step-up transformer

Transformer that increases voltage and decreases current.

Step-down transformer

Transformer that decreases voltage and increases current.

Turns ratio greater than 1

Step-up transformer characteristic.

Turns ratio less than 1

Step-down transformer characteristic.

High-voltage transformer

Example of step-up transformer in x-ray circuit.

Filament transformer

Example of step-down transformer in x-ray circuit.

Resistance loss

Loss caused by resistance in transformer wires.

Hysteresis loss

Loss caused by reversal of magnetic domains in the core.

Eddy current loss

Loss caused by induced currents in the core opposing the magnetic field.

Closed-core laminated construction

Method to reduce eddy current loss.

Closed-core transformer

Transformer type made of laminated iron layers to reduce losses.

Autotransformer

Transformer type with one winding acting as both primary and secondary.

Shell-type transformer

Transformer type where secondary is wrapped around the primary for higher efficiency.