Electric Potential and Capacitors - Vocabulary Flashcards

Vocabulary flashcards covering key terms related to electric potential, potential energy, electric fields, equipotentials, and parallel-plate capacitors from pages 11–20 of the notes.

Electric Potential (V)

The electric potential at a point due to source charges; the potential energy per unit charge; exists whether or not a test charge is present. Measured in volts (V) or J/C.

Electric Potential Energy (U_elec)

The interaction energy of a charged particle with source charges; measured in joules (J).

Potential (V) = U/q

Electric potential at a point equals the potential energy per unit charge: V = U/q.

Electric Field (E)

Force per unit charge; for a uniform field between plates, E = ΔV/d. Units are N/C or V/m.

Potential Difference (ΔV)

Difference in electric potential between two points; ΔV = V2 − V1; measured in volts (V).

Uniform Electric Field

An electric field with the same strength at all points between the plates; produced by a parallel-plate capacitor.

Parallel-Plate Capacitor

Two flat metal plates facing each other with opposite charges; create a uniform electric field between them.

V(x) in a Uniform Field

The potential at position x between plates increases linearly: V(x) = (ΔV/d) x.

Equipotential

A surface where the electric potential is the same everywhere; moving a charge along it requires no work.

Equipotential Surface/Line

Isopotential surface (3D) or line (2D) where V is constant.

Work (W) to Move a Charge

Energy required to move a charge; in a uniform field, W = q E x; moving against the field requires positive work.

Potential Energy in a Uniform Field

U = q E x for a charge q moved distance x in a uniform electric field E.

ΔV = E d

Voltage across a uniform field equals field strength times plate separation.

E = ΔV/d

Electric field magnitude equals potential difference divided by distance between plates.

Zero Potential Reference

We may set V = 0 at a chosen location (e.g., negative plate); potential then increases toward the positive plate.

Battery (in this context)

Device that fixes the voltage between the plates; determines ΔV and thus the electric field given plate spacing.

Cell Membrane as Capacitor

Biological membranes act like parallel-plate capacitors; typical thickness ~7.0 nm, ΔV ~70 mV, yielding E ~1.0×10^7 V/m.

Point-Charge Potential V(r)

Potential due to a point source charge: V(r) = k q / r, with k ≈ 8.988×10^9 N·m^2/C^2.

Potential Energy of a Test Charge near a Point Charge

U = q' V = k q q' / r; energy of a test charge q' at distance r from source charge q.

Infinity Reference for Potential

V(∞) = 0; the potential from a point charge falls off as 1/r and is set to zero at infinity.

Sign of Potential

If the source charge q is positive, V(r) is positive; if q is negative, V(r) is negative.

Coulomb's Constant (k)

k = 8.988×10^9 N·m^2/C^2; appears in V(r) = k q / r and U = q' V.