Electrostatics and Capacitors – Key Vocabulary

Vocabulary flashcards covering core terms from the notes on electrostatics, electric fields, Gauss's law, dipoles, and capacitors.

Charge

Inherent property carried by protons and electrons; sign convention assigns positive to protons and negative to electrons; symbol e, with e = 1.6×10^-19 C.

Elementary Charge (e)

The magnitude of electric charge on a proton or electron (approximately 1.6×10^-19 coulombs).

Quantization of Charge

Electric charges occur only in discrete amounts, integral multiples of e.

Conservation of Charge

In an isolated system, total charge remains constant; charge is neither created nor destroyed but can be transferred.

Coulomb's Law

The force between two stationary point charges is F = k q1 q2 / r^2.

Coulomb's Constant (k)

k = 9×10^9 N·m^2·C^-2; equals 1/(4π ε0).

Permittivity of Free Space (ε0)

ε0 ≈ 8.85×10^-12 C^2/(N·m^2); a constant in Coulomb’s law and capacitor calculations.

Electric Field (E)

Force per unit positive test charge; E = F/q; for a point charge, E = (1/4πε0) q / r^2 in the radial direction.

Test Charge

A small positive charge used to probe the electric field.

Field Lines (Lines of Force)

Visual representation of the electric field; direction is tangent to lines; density indicates field strength.

Gauss's Law

The net electric flux through a closed surface equals q_enclosed / ε0.

Surface Charge Density (σ)

Charge per unit area on a surface.

Linear Charge Density (λ)

Charge per unit length along a line charge.

Volume Charge Density (ρ)

Charge per unit volume.

Infinite Sheet of Charge

Electric field perpendicular to the sheet: E⊥ = σ/(2ε0); E∥ = 0; field is uniform on both sides.

Capacitance (C)

C = Q/V; unit is the farad (F); depends on geometry and dielectric, not on Q or V individually.

Dielectric Constant (ε_r / κ)

Factor by which a dielectric increases capacitance; C' = ε_r C (or C' = κ C for relative permittivity κ).

Parallel Plate Capacitor

Capacitor with two parallel plates; C = ε0 A/d; E = σ/ε0; V = Ed.

Energy Stored in a Capacitor

W = 1/2 C V^2 = Q^2/(2C) (work required to charge the capacitor).

Q = C V

Relation between charge, capacitance, and potential difference.

Dipole Moment (p)

For a pair of charges ±q separated by distance d, p = qd (vector from negative to positive charge).

Torque on a Dipole in a Uniform Field

τ = p × E; magnitude τ = p E sinθ, tending to align the dipole with the field.

Potential Energy of a Dipole in a Field

U = - p · E; minimum when dipole aligns with the field.