ELECTRICITY, MAGNETISM, ELECTROMAGNETISM

Electromagnetism

Branch of physics that studies the relationship between electricity and magnetism and the phenomena arising from their interaction.

Voltaic Pile

Early battery invented by Alessandro Volta consisting of stacked zinc-copper cells that produced a continuous electric current.

Dry Cell

A type of primary (non-rechargeable) battery that utilizes a carbon rod as the positive electrode (cathode), a zinc container as the negative electrode (anode), and an electrolytic paste (often ammonium chloride) as the electrolyte to generate direct electric current via chemical reactions.

Hans Oersted

Danish physicist who first demonstrated that an electric current generates a magnetic field (1820).

Oersted Experiment

Observation that a compass needle deflects when placed near a current-carrying wire, proving electricity produces magnetism.

Electromagnetic Induction

Process in which an electric current is generated in a conductor when it experiences a changing magnetic field.

Michael Faraday

British scientist who discovered electromagnetic induction and formulated Faraday’s Law describing induced currents.

Faraday’s Law

Law stating that the magnitude of an induced current depends on magnetic-field strength, velocity, angle, and number of conductor turns.

Ammeter

Instrument used to measure current

Mutual Induction

Induction of an EMF in one circuit caused by a changing current in a neighboring circuit (e.g., high-voltage transformer).

Self-Induction

Induction of an EMF within a single coil that opposes changes in the current flowing through the coil (e.g., autotransformer).

Solenoid

Helical coil of wire whose magnetic field is concentrated through its center when current flows.

Electromagnet

Coil of wire wrapped around ferromagnetic material; its magnetic field intensity is controlled by the current through the coil.

Electric Motor

Device that converts electrical energy into mechanical motion; based on force exerted on current-carrying conductors in a magnetic field.

Electric Generator

Device that converts mechanical motion into electrical energy by electromagnetic induction.

Induction Motor

Motor whose rotor is turned by a rotating magnetic field produced by sequentially energized stator windings; used in x-ray tube anodes.

Rotor

Rotating shaft in an induction motor made of copper and soft iron bars that spins within the magnetic field.

Stator

Stationary set of electromagnets surrounding the rotor in an induction motor; produces the rotating magnetic field.

Transformer

Device that changes AC voltage and current by mutual induction between primary and secondary windings around a ferromagnetic core.

Primary Coil

Input winding of a transformer that receives alternating current and creates the changing magnetic field.

Secondary Coil

Output winding of a transformer in which the changing magnetic field induces a new alternating current.

Turns Ratio (Ns/Np)

Ratio of the number of turns in the secondary coil to the primary coil; determines the voltage change in a transformer.

Step-Up Transformer

Transformer with a turns ratio greater than 1 that increases voltage and proportionally decreases current on the secondary side.

Step-Down Transformer

Transformer with a turns ratio less than 1 that decreases voltage and proportionally increases current on the secondary side.

Resistance

Power loss in transformer windings due to electrical resistance, manifested as heat.

Hysteresis Loss

Energy loss in transformer cores caused by repeated magnetization reversals in alternating current.

Eddy Current

Energy loss due to currents induced in the core that oppose the inducing magnetic field; minimized by laminated cores.

Closed-Core Transformer

Transformer whose laminated ferromagnetic core is built up of laminated layers of irons, reducing energy losses which results in greater efficiency

Autotransformer

Single-winding transformer where part of the coil acts as both primary and secondary; provides small voltage adjustments.

Shell-Type Transformer

Highly efficient transformer with two closed cores and secondary winding wrapped around the primary; The most currently used

Electromechanical Device

Any apparatus, such as motors or generators, that converts electrical energy to mechanical energy or vice versa via electromagnetic principles.

Faraday’s Four Factors

1) Magnetic-field strength, 2) Velocity of the field relative to the conductor, 3) Angle between field and conductor, 4) Number of turns in the conductor—together dictate induced EMF magnitude.

Transformer Law (Current)

Current change across a transformer is inversely proportional to the voltage change: Is/Ip = Np/Ns.

Magnetism

A fundamental property of certain materials that enables them to produce and respond to magnetic fields.

Magnetite (Fe3O4)

Naturally occurring iron oxide first discovered near Magnesia; exhibits strong magnetic properties.

Lodestone

A naturally magnetized piece of magnetite historically used as the first magnetic compass.

Magnet

Any material that produces a magnetic field and possesses north and south poles.

Dipolar (Bipolar)

Describes magnets that always have two poles—north and south.

Pole (North/South)

One of the two ends of a magnet where magnetic field lines emerge (north) or enter (south).

Lines of Force (Lines of Flux)

Imaginary lines representing the direction and strength of a magnetic field; flow from north to south outside a magnet.

Gauss’s Law for Magnetism

States that the net magnetic flux through a closed surface is zero; magnetic monopoles do not exist.

Magnetic Field

The region around a magnet or moving charge where magnetic forces can be detected.

Magnetic Flux (Weber, Wb)

Total number of magnetic field lines passing through a surface; 1 Wb equals 10^8 lines of flux.

Magnetic Flux Density

Amount of magnetic flux per unit area; measured in tesla (T) or gauss (G).

Tesla (T)

SI unit of magnetic flux density; 1 T = 10,000 gauss or 1 Wb/m².

Gauss (G)

CGS unit of magnetic flux density; 10,000 G equal 1 tesla.

Electron Spin

Intrinsic rotation of electrons that creates tiny magnetic fields contributing to atom’s overall magnetism.

Magnetic Dipole

Smallest unit of magnetism produced by a single electron orbit or spin; has two poles.

Magnetic Domain

Group of atoms whose magnetic dipoles are aligned in the same direction.

Domain Theory of Magnetism

Explains magnetism by the alignment of 10^15 or more atomic dipoles forming domains.

Permeability

Ease with which a material can be magnetized (aligned dipoles).

Retentivity

Ability of a material to retain its magnetization after the external field is removed.

Nonmagnetic Material

Substance such as wood or glass that is essentially unaffected by magnetic fields.

Diamagnetic Material

Material like water or plastic that is weakly repelled by both magnetic poles.

Paramagnetic Material

Material such as gadolinium that is weakly attracted to both magnetic poles.

Ferromagnetic Material

Substance (iron, nickel, cobalt) that can be strongly magnetized due to high permeability.

Alnico

One of the most useful magnets produced from ferromagnetic material (iron, nickel, cobalt)

Rare-Earth Ceramic Magnet

Modern ferromagnetic material (e.g., neodymium) providing very strong magnetic fields.

Naturally Occurring Magnet

Magnetic objects like Earth itself or lodestones found in nature.

Artificially Induced Permanent Magnet

Man-made magnet (bar or horseshoe) usually formed from iron; can lose magnetism by heating or striking.

Electromagnet

Magnet consisting of a coil of wire wound around an iron core; magnetic field exists only when electric current flows.

Magnetic Induction

Process of magnetizing a material by an external magnetic field, aligning its domains.

Magnetic Shielding

Use of ferromagnetic materials to draw in and contain fringe magnetic fields (e.g., MRI room shields).

Inverse Square Law (Magnetism)

Magnetic force between two fields is directly proportional to their strengths and inversely proportional to the square of the distance separating them.

Maxwell’s Field Theory

Unified description showing electric and magnetic forces behave similarly and propagate as electromagnetic waves.

Magnetic Moment

Magnetic dipole produced by spinning charges such as the proton in a hydrogen nucleus; basis of MRI.

Magnetic Permeability (μ)

Measure of how a material concentrates magnetic lines of force; high μ indicates strong attraction of flux lines.

Earth’s Magnetic Field

Weak field (~50 μT at equator, 100 μT at poles) behaving like a giant bar magnet tilted relative to geographic poles.

Repulsion-Attraction Law

Like poles repel each other, while unlike poles attract.

Magnetic Lines of Induction

Imaginary field lines whose density indicates magnetic field intensity; used to visualize induced magnetism.

Electricity

A form of energy resulting from the flow of charged particles (electrons).

Electric Current

The flow of electrons along a conductor; measured in amperes (A).

Electrostatics

The study of stationary electric charges.

Electron

Sub-atomic particle with one unit of negative charge.

Proton

Sub-atomic particle with one unit of positive charge.

Electric Charge

A property of matter that can be positive or negative and causes electrical interactions.

Coulomb (C)

The fundamental unit of electric charge; 1 C = 6.3 × 10¹⁸ electron charges.

Ion

An atom that has gained or lost electrons and therefore carries a net charge.

Cation

A positively charged ion formed by loss of electrons.

Anion

A negatively charged ion formed by gain of electrons.

Electrification

The process of adding or removing electrons to charge an object.

Friction (electrification)

Charging produced when two objects are rubbed together and electrons transfer.

Contact (electrification)

Charging that occurs when two objects touch, allowing electrons to flow and equalize charge.

Induction (electrification)

Charging of an uncharged object by the electric field of a nearby charged body without contact.

Electric Ground

The Earth, acting as a vast reservoir to absorb or supply electric charge.

Electric Field

The region surrounding a charged object where electric forces are exerted on other charges.

Electrostatic Force

Attractive or repulsive force between electric charges due to their electric fields.

Coulomb’s Law

States that the electrostatic force (F) between two point charges (Q₁ and Q₂) is directly proportional to the product of their magnitudes and inversely proportional to the square of the distance (d) between them. It is given by the formula F = k(Q₁Q₂)/d², where k is Coulomb's constant.

Charge Distribution Law

Electric charge on a conductor spreads uniformly over its surface.

Charge Concentration Law

Electric charge accumulates at the sharpest curvature of a conductor’s surface.

Electric Potential

Stored electrical energy per unit charge; ability to do work when released.

Voltage

Electric potential difference between two points; higher voltage = greater potential to do work.

Electromotive Force (EMF)

Alternative term for electric potential or voltage that drives current.

Volt (V)

Unit of electric potential; 1 V = 1 joule per coulomb (J/C).

Ampere (A)

Unit of electric current; 1 A = 1 coulomb of charge per second.

Conductor

Material (e.g., copper) through which electrons flow easily.

Insulator

Material that resists electron flow (e.g., rubber, glass).

Semiconductor

Material that behaves as conductor or insulator depending on conditions (e.g., silicon).

Superconductor

Material with zero electrical resistance below a critical temperature.

Resistance

Opposition to current flow, producing heat; measured in ohms (Ω).