Chapter 20: Electric Fields and Forces - Vocabulary Flashcards

Vocabulary flashcards covering key terms, definitions, and concepts from the lecture notes on charges, fields, and forces.

Electric charge

A fundamental property of matter with two kinds: positive and negative. Objects are charged when there is an imbalance between protons and electrons; charge is conserved.

Positive charge

Charge carried by protons; produced when an object has more positive charge than negative; electrons are removed.

Negative charge

Charge carried by electrons; produced when an object has more negative charge than positive.

Neutral object

An object with equal amounts of positive and negative charge; net charge is zero, though it may still contain separated charges.

Proton

Positively charged particle in the nucleus; charge +e.

Electron

Negatively charged particle surrounding the nucleus; charge −e.

Ionization

The process of removing (or gaining) electrons from an atom, creating ions.

Ion

An atom with a net electric charge due to loss or gain of electrons (positive or negative).

Coulomb’s Law

F = k q1 q2 / r^2, force between two point charges; along the line joining them; repulsive for like charges, attractive for opposite charges.

Electrostatic constant (k)

Constant in Coulomb’s Law, approximately 8.99 × 10^9 N·m^2/C^2.

Electric field

The force per unit charge that a source charge would exert on a test charge; a vector field defined at every point in space; E = F/q.

Electric field strength

Magnitude of the electric field, denoted E; units are N/C.

Point charge

An idealized charge located at a single point; produces a radially varying field with E = kq/r^2.

Electric field due to a point charge

E = k q / r^2 in the radial direction (away from a positive charge, toward a negative charge).

Permittivity of free space (epsilon0)

Constant ε0 ≈ 8.85 × 10^−12 C^2/(N·m^2); relates charge, field, and geometry (e.g., between capacitor plates).

Parallel-plate capacitor

Two closely spaced conducting plates with opposite charges, producing a uniform electric field between them.

Charge density (sigma)

Charge per unit area, σ = Q/A; determines the field between plates via E = σ/ε0 = Q/(ε0 A).

Uniform electric field

An electric field with the same magnitude and direction at all points between the plates.

Electric field lines

Imaginary lines representing the field; start on positive charges, end on negative; tangents indicate field direction; lines do not cross and crowding indicates stronger field.

Dipole

Two equal and opposite charges separated by a distance; net charge is zero but there is a nonzero electric field.

Dipole moment (p)

Vector from the negative to the positive charge with magnitude p = qd.

Torque on a dipole

τ = p × E; causes a dipole to rotate to align with the external field.

Polarization

Induced separation of charges within an object in an external field; neutral objects can become polarized.

Hydrogen bonding

Weak bond between a hydrogen attached to one electronegative atom and a neighboring electronegative atom; important in water and biology.

Conductor

Material in which electric charges move easily; in electrostatic equilibrium, excess charge resides on the surface.

Insulator

Material in which charges are immobile; charging can leave surface patches of charge but charges do not move freely.

Surface charge

Excess charge that resides on the surface of a conductor; density can be higher at sharp points.

Screening (Faraday cage)

A conducting enclosure that excludes external electric fields; field inside is zero in electrostatic equilibrium.

Charge conservation

Charge cannot be created or destroyed; it is conserved in closed systems.

Charging by friction

Charging a material by rubbing, transferring charge from one object to another.

Charging by contact (discharging)

Charge transfer between objects through direct contact; discharging is the removal of charge.

Superposition (electric fields)

The net electric field is the vector sum of the fields from all charges.

Neutral object’s charge distribution

A neutral object has equal positive and negative charges; can still be polarized by external charges.

Proton charge

Positive elementary charge, +e.

Electron charge

Negative elementary charge, −e.

Field strength vs field lines

Field strength corresponds to vector magnitude; field lines density reflects strength; lines illustrate direction but do not capture all vector details.

Field direction for negative test charge

Field direction is defined as the direction of the force on a positive test charge; for a negative test charge, the actual force is opposite to the field direction.

Ionization energy concept (brief)

Energy required to remove an electron from an atom; relates to how easily charges can be transferred.