Electricity and Magnetism Vocabulary

Vocabulary flashcards based on lecture notes about electricity and magnetism.

Electric Charge

A fundamental property of matter that enables participation in electromagnetic interactions.

Ions

Charged atoms formed by gaining or losing electrons.

Conductors

Materials with free-moving outer electrons, allowing charges to distribute readily (e.g., copper, aluminum, silver).

Insulators

Materials where electrons are tightly bound to atoms, limiting free movement (e.g., glass, rubber, wood).

Semiconductors

Materials with electrical properties between conductors and insulators, modifiable by adding specific atoms (e.g., silicon, germanium).

Induction

Charges redistribute within a conductor when brought near an external charge, without direct contact; creating induced charges on the surface.

Polarization (in Insulators)

External charges disturb atomic structure, causing electron-nucleus separation and creating atomic dipoles.

Coulomb (C)

SI unit of charge.

Electric Field

A field force that acts through space without physical contact.

Electrostatic Equilibrium

The electric field inside a conductor is zero.

Equipotential Lines and Surfaces

Lines or surfaces in a voltage field where the electric potential (voltage) is constant.

Capacitors

Devices designed to store electric charge and, consequently, electric potential energy.

Dielectrics

Nonconducting materials inserted between capacitor plates, which increase the capacitance.

Electric Current

Electric current (I) is the rate of flow of electric charge through a given region of space.

Conventional Current

Defined as the direction in which positive charges would flow.

Drift Velocity (v_d)

The average velocity of charge carriers in a material due to an electric field. It's typically very small.

Current Density (J)

A vector quantity representing the current per unit cross-sectional area (J = I/A). Its direction is the direction of current flow.

Resistance (R)

The opposition a material offers to the flow of electric current.

Ohmic Materials

Materials that obey Ohm's Law, meaning their resistance is constant over a wide range of voltages (e.g., most metals).

Non-Ohmic Materials

Materials that do not obey Ohm's Law; their resistance varies with voltage or current (e.g., semiconductors, diodes).

Resistivity (ρ)

An intrinsic property of a material that quantifies its resistance to current flow (ρ = E/J). It's the inverse of conductivity (ρ = 1/σ).

Superconductors

Materials that exhibit zero electrical resistance when cooled below a critical temperature (T_c).

Electric Power

The rate at which energy is transferred or converted in an electric circuit.

Electromotive Force (EMF, ε)

The ideal, maximum voltage a battery can provide when no current is being drawn from it (open circuit voltage).

Internal Resistance (r)

All real batteries have some internal resistance, which causes a voltage drop (Ir) when current flows through them.

Terminal Voltage (ΔV_terminal)

The actual voltage available at the battery's terminals when it's in use.

Junction Rule (Kirchhoff's Current Law)

States that the sum of currents entering any junction in a circuit must equal the sum of currents leaving that junction. This rule is a direct consequence of the conservation of electric charge.

Loop Rule (Kirchhoff's Voltage Law - KVL)

The algebraic sum of all potential differences (voltage changes) around any closed loop in a circuit must be zero.

Time Constant (τ)

Represent the time required for the charge (or current) in the circuit to change by a factor of (1 - 1/e) ≈ 63.2% during charging, or to fall to 1/e ≈ 36.8% of its initial value during discharging.

Ground Fault Interrupters (GFIs)

Detect small imbalances in current between the live and neutral wires, indicating a "ground fault" (current flowing through an unintended path, like a person), and quickly trip the circuit.

Origin of Magnetism

Magnetic fields are produced by moving electric charges (electric currents).

Magnetic Field Lines

Represent the direction of the magnetic field (B) at any point (tangent to the line).

Torque on a Current Loop (Electric Motors)

A current loop placed in a magnetic field experiences a torque that tends to align its magnetic moment with the external field. This principle is fundamental to electric motors.

Sources of Magnetic Fields

Only moving charges (currents) produce magnetic fields.

Diamagnetic Materials

Weakly repelled by magnetic fields (e.g., water, copper).

Paramagnetic Materials

Weakly attracted to magnetic fields; their atomic magnetic moments align slightly with an external field but return to random orientation when the field is removed (e.g., aluminum, platinum).

Ferromagnetic Materials

Strongly attracted to magnetic fields and can retain magnetization after the external field is removed (e.g., iron, nickel, cobalt).

Magnetic Flux (Φ_B)

The amount of magnetic field passing through a given area.

Lenz's Law

The direction of the induced current or induced emf is always such that the magnetic field it produces opposes the change in magnetic flux that caused it.

Motional EMF

An emf induced across a conductor moving through a uniform magnetic field.

Generators

Devices that convert mechanical energy into electrical energy by rotating a coil in a magnetic field, thereby continuously changing the magnetic flux and inducing an alternating emf.

Eddy Currents

Circulating currents induced in bulk conductors when they experience a changing magnetic flux.

Mutual Inductance (M)

When a changing current in one coil (primary) induces an emf in a nearby second coil (secondary).

Self-Inductance (L)

When a changing current in a single coil induces an emf within the same coil, opposing the change in current.

Poynting Vector (S)

Describes the direction and rate of energy flow per unit area of an electromagnetic wave. Its magnitude represents the wave's intensity.