Chapter 21: Electric Potential and Capacitors – Vocabulary Flashcards

Vocabulary flashcards covering key concepts from Chapter 21: Electric Potential, Electric Potential Energy, Electric Field, Capacitance, Dielectrics, and related equations.

Electric potential

The potential energy per unit charge at a point in an electric field. Measured in volts (V); created by source charges and represents the potential to create electric potential energy.

Electric potential energy (Uelec)

Energy that a charge would have due to its position in an electric potential; Uelec = qV for a charge q in a potential V.

Work (in electric context)

Energy transferred when a force moves a charge through a distance in an electric field; related to changes in electric potential energy (W = ΔUelec) and to F·d.

Potential difference (ΔV)

The difference in electric potential between two points; work done per unit charge to move a test charge between those points; ΔU = qΔV.

Electric field (E)

A region around charges that exerts a force F = qE on a test charge; exists whether or not a test charge is present; for a uniform field, E ≈ ΔV/Δx.

Source charges

Charges that create the electric field and electric potential in space.

Equipotential

A surface or line where the electric potential is the same everywhere; moving a charge along an equipotential requires no work; equipotentials are perpendicular to the electric field.

Capacitance (C)

The ratio of charge to the potential difference on a capacitor, C = Q/ΔV; unit is the farad (F).

Dielectric

An insulating material placed between capacitor plates that becomes polarized and increases the capacitor’s capacitance.

Dielectric constant (κ)

A factor by which a dielectric increases capacitance: C = κC0; κ > 1 for most dielectrics; table values vary by material.

Parallel-plate capacitor

A capacitor formed by two conducting plates separated by a small distance; produces a nearly uniform electric field; C = ε0A/d; E = ΔV/d; U = 1/2 CV^2.

Potential energy of a point charge (two-charge form)

U = k q q' / r, the interaction energy between two point charges separated by r; positive for like charges, negative for opposite charges.

Potential due to a point charge

V = kq/r, the electric potential at distance r from a point charge q (k = 1/(4πε0)).

Superposition of potentials

The total electric potential at a point from multiple charges is the sum of individual potentials: V = Σ k qi/ri.

Electron volt (eV)

A unit of energy equal to the work done moving a charge of magnitude e through a potential difference of 1 V; 1 eV ≈ 1.60×10^-19 J.

Energy stored in a capacitor

U = (1/2)CV^2 = (1/2)QV = Q^2/(2C); energy stored in the electric field between the capacitor plates.

Energy density of the electric field

uE = (1/2) ε E^2; the energy per unit volume stored in the electric field; total energy U = uE × (volume).

Permittivity (ε)

ε = ε0κ; ε0 ≈ 8.85×10^-12 F/m is the vacuum permittivity; κ is the dielectric constant of the material; determines how fields propagate in a medium.

Electric field inside a parallel-plate capacitor

A uniform field between plates; E = ΔV/d; potential varies linearly with position: V(x) = Ex; capacitor voltage relates to plate separation and area.

Charging a capacitor with a battery

When connected to a battery, the capacitor voltage equals the battery voltage (Vc = Vbat) and the plate charge is Q = C V.

Conductor in electrostatic equilibrium

Inside the conductor: E = 0; excess charge resides on the surface; surface is an equipotential; exterior field is perpendicular to the surface; entire conductor is at the same potential.

Ionization energy

Energy required to remove an electron from an atom; often measured in eV (examples include ~9–10 eV for some atoms).

Potential of a point charge (summary relation)

V = kq/r; the potential at distance r from a point charge q; used to find potential energy via U = qV.

Energy and potential for dielectric insertion

Inserting a dielectric between capacitor plates increases capacitance (C → κC0), reduces the field and potential difference for fixed charge, and raises energy storage capacity via U = (1/2)CV^2.

Electric potential and field relation (general)

E = -∇V; the electric field is perpendicular to equipotential surfaces; the magnitude of E relates to the rate of change of V in space.

Dipole equipotentials

The equipotential map for a dipole is the superposition of potentials from the positive and negative charges; V at a point is the sum of those contributions.

Capacitance formula with geometry

For a parallel-plate capacitor, C = ε0A/d; inserting a dielectric changes ε to ε = κε0 and scales C by κ.

Energy stored in a dielectric-filled capacitor

The energy remains U = (1/2)CV^2, but with the dielectric, the energy density and total energy are increased due to higher C (via κ).