Electromagnetism

Vocabulary practice flashcards covering fundamental electromagnetism, magnetic units, induction laws, motors, generators, transformer types and equations, and rectification circuits.

Oersted's Discovery

The principle discovered by Hans Christian Oersted establishing that any moving electrical charge produces a magnetic field.

Magnetite (Lodestone)

A natural magnetic oxide rod-type stone discovered around 1000 BC in Magnesia that rotates back and forth when suspended by a string; also known as a leading stone.

Spinning Magnetic Moment (Dipole)

The magnetic field produced by an electron spinning upon its own axis as it orbits the nucleus of an atom.

Magnetic Domain

A microscopic cluster of atoms whose magnetic dipole axes are aligned in the same direction to establish a unified magnetic field.

Weber ($\text{Wb}$)

The SI unit of magnetic flux, defined as $1\,\text{Wb} = 10^8\,\text{lines of flux}$.

Tesla ($\text{T}$)

The standard unit of magnetic flux density, where $1\,\text{T} = 1 \times 10^4\,\text{Gauss}$.

Earth's Magnetic Field

The magnetic field generated by Earth's rotation, possessing an approximate strength of $1 \times 10^{-4}\,\text{T}$, $1\,\text{Gauss}$, or $1 \times 10^6\,\text{lines of flux/m}^2$.

Magnetic Lines of Force

Closed imaginary loops that represent field intensity, directed from north to south outside a magnet and from south to north inside a magnet.

Law of Magnetic Poles

The fundamental magnetic rule stating that like magnetic poles repel each other, whereas opposite (unlike) magnetic poles attract.

Inverse Square Law for Magnetism

The physical law stating that magnetic force between two fields is directly proportional to the product of their magnitudes and inversely proportional to the square of the distance separating them ($\frac{I_1}{I_2} = \frac{d_2^2}{d_1^2}$).

Magnetic Induction

The process by which certain materials become magnetized when brought into the presence of an external magnetic field.

Permeability

The ease with which a given material can be magnetized.

Retentivity

The ability of a material to resist demagnetization and retain its magnetic properties over time.

Ferromagnetic Material

A material characterized by high permeability and ease of magnetization, forming a standard magnet.

Paramagnetic Material

A material that displays weak magnetic properties and is difficult to magnetize.

Diamagnetic Material

A substance that repels magnetic fields rather than being attracted to them.

Nonmagnetic Material

A material that cannot be magnetized under any circumstances.

Natural Magnet

A naturally occurring magnet, such as lodestone, formed when iron oxide remains subjected to Earth's magnetic field over eons.

Artificial Permanent Magnet

A manufactured magnet created by heating a steel alloy (such as alnico), subjecting it to an intense magnetic field, and allowing it to cool.

Solenoid

A helical coil of wire that produces a magnetic field when an electric current flows through its loops.

Electromagnet

A temporary magnet constructed by inserting a ferromagnetic core inside a current-carrying solenoid coil, which loses its magnetism when the current stops.

Faraday's Law

The first law of electromagnetics stating that induced EMF is directly proportional to the rate of change of magnetic flux, determined by field strength, speed of relative motion, angle between lines of force and conductor, and number of turns in the coil.

Lenz's Law

The second law of electromagnetics stating that an induced current always sets up a secondary magnetic field that opposes the original action or change producing it.

Mutual Induction

The process wherein a fluctuating current supplied to a primary coil induces a proportional secondary current in an adjacent, unlinked secondary coil.

Self-Induction

The induction of an opposing voltage within a single coil caused by the expansion and collapse of its own magnetic lines of force during current variations.

Inductive Reactance

The opposing electrical force (potential difference and resistance) that resists the flow and reversal of current in an alternating current circuit.

Electric Generator (Dynamo)

A mechanical device that converts mechanical energy into electrical energy, consisting primarily of an armature coil rotating within a magnetic field.

Slip Rings

Continuous conductive metal rings in an AC generator that maintain an electrical connection between the rotating armature and stationary circuit to produce alternating current.

Commutator

A segmented split-ring switch used in DC generators and motors to mechanical reverse circuit connections and maintain current flowing in a single unidirectional path.

Impedance ($Z$)

The total effective resistance to current flow in an alternating current circuit, modifying Ohm's law to $I = \frac{V}{Z}$.

Synchronous AC Motor

An alternating current motor whose rotor coils turn in synchrony with the exact rotational speed of the generator supplying the current.

Induction Motor

An electric motor featuring a rotor driven by a rotating magnetic field generated by sequential pairs of external electromagnets (stator).

Stator

The stationary outer ring of an electric motor containing paired electromagnets that produce a changing magnetic field around the rotor.

Milliammeter (mA Meter)

An instrument positioned between the rectifier and the X-ray tube in an X-ray circuit to measure tube current in milliamperes.

Galvanometer

A sensitive electrical measuring meter designed for direct current (DC) circuits that utilizes permanent magnets.

Dynameter

An instrument designed for alternating current (AC) circuits that measures electrical current using electromagnets.

Transformer

An electrical device that transforms voltage and current in an AC circuit via mutual induction across primary and secondary windings.

Transformer Core Types

The structural configurations of transformer cores: (A) Air core, (B) Open core, (C) Closed core, and (D) Shell type.

Copper Loss ($I^2R$ Loss)

Power dissipation in a transformer caused by inherent electrical resistance within the copper wire windings.

Hysteresis Loss (Lagging Loss)

Energy loss occurring in a transformer core due to constant magnetic domain realignment caused by reversing AC magnetic flux.

Eddy Current Loss

Heat dissipation in a transformer core produced by swirling opposing electrical currents, minimized by laminating core plates.

Transformer Law

The principle stating that voltage is directly proportional to coil turns ($\frac{V_s}{V_p} = \frac{N_s}{N_p}$), while current is inversely proportional ($\frac{I_s}{I_p} = \frac{N_p}{N_s}$).

Step-Up Transformer

A transformer in which the secondary winding contains more turns than the primary ($N_s > N_p$), increasing voltage while decreasing amperage.

Step-Down Transformer

A transformer where the primary winding contains more turns than the secondary ($N_p > N_s$), decreasing voltage while increasing amperage.

Autotransformer

A variable transformer operating on self-induction that utilizes a single continuous coil tapped at varying positions to select line voltage ($\text{kVp}$).

Capacitor

A component consisting of two oppositely charged plates separated by a dielectric material that stores electrostatic charge, measured in farads ($C = \frac{q}{V}$).

Half-Wave Rectification

The process of converting alternating current to pulsating direct current where only one half of the AC cycle passes and the reverse-biased cycle drops to $0\,\text{V}$.

Full-Wave Rectification

The rectification method employing at least four diodes in a bridge arrangement to invert negative AC half-cycles into continuous unidirectional pulses.