Electric Charges and Fields – Core Vocabulary

Key vocabulary terms and definitions covering electric charge, Coulomb’s law, electric field concepts, Gauss’s law, and related quantities from the lecture notes on Electric Charges and Fields.

Electrostatics

Branch of physics that studies forces, fields and potentials arising from static electric charges.

Electric Charge

Intrinsic property of matter that causes it to experience an electric force; comes in two kinds, positive and negative.

Polarity of Charge

Property that distinguishes the two kinds of electric charge; like charges repel and unlike charges attract.

Conductor

Material that readily allows electric charge (usually electrons) to move through it; e.g., metals, human body, Earth.

Insulator

Material that offers high resistance to movement of electric charge; e.g., glass, plastic, wood.

Semiconductor

Material whose electrical conductivity lies between that of conductors and insulators.

Additivity of Charge

Total charge of a system equals the algebraic sum of individual charges (charges add like scalars).

Conservation of Charge

Net electric charge of an isolated system remains constant; charges can neither be created nor destroyed.

Quantisation of Charge

Electric charge exists only in integral multiples of the elementary charge e (1.602 × 10⁻¹⁹ C).

Coulomb’s Law

Magnitude of electrostatic force between two point charges is F = k |q₁q₂| / r², directed along the line joining them.

Coulomb Constant (k)

Proportionality constant in Coulomb’s law; k = 1 / (4πɛ₀) ≈ 9 × 10⁹ N·m²·C⁻².

Permittivity of Free Space (ɛ₀)

Physical constant measuring the ability of vacuum to permit electric field lines; ɛ₀ = 8.854 × 10⁻¹² C²·N⁻¹·m⁻².

Superposition Principle

Net electric force (or field) on a charge equals the vector sum of forces (or fields) due to all other charges taken individually.

Electric Field (E)

Vector quantity defined as force per unit positive test charge at a point: E = F / q₀.

Test Charge

Hypothetical infinitesimal charge used to probe an electric field without disturbing the source distribution.

Source Charge

Charge or distribution of charges that produces an electric field in space.

Electric Field Lines

Imaginary curves whose tangents give the direction of electric field; density of lines indicates field strength.

Electric Flux (Φ)

Measure of the number of electric field lines passing through an area; Φ = E·ΔS = EΔS cosθ.

Gaussian Surface

Closed surface chosen to apply Gauss’s law for calculating electric flux and enclosed charge.

Gauss’s Law

Total electric flux through any closed surface equals the enclosed charge divided by ɛ₀: Φ = q_encl / ɛ₀.

Electric Dipole

System of two equal and opposite charges separated by a small distance 2a.

Dipole Moment (p)

Vector quantity p = q·(2a) directed from negative to positive charge; measures the strength of a dipole.

Torque on a Dipole

In a uniform field, τ = p × E; tends to align the dipole with the field.

Line Charge Density (λ)

Charge per unit length on a line: λ = ΔQ / Δl (C·m⁻¹).

Surface Charge Density (σ)

Charge per unit area on a surface: σ = ΔQ / ΔS (C·m⁻²).

Volume Charge Density (ρ)

Charge per unit volume: ρ = ΔQ / ΔV (C·m⁻³).

Field of Infinite Line Charge

Electric field magnitude E = λ / (2πɛ₀r), radial from the line.

Field of Infinite Plane Sheet

Electric field magnitude E = σ / (2ɛ₀), normal to the sheet and independent of distance.

Field Inside Charged Shell

Electric field inside a uniformly charged thin spherical shell is zero (E = 0 for r < R).

Field Outside Charged Shell

Electric field outside a uniformly charged thin spherical shell behaves as if all charge were at the centre: E = (1/4πɛ₀)·(q/r²).