Chapter 25: Electric Potential

25 practice flashcards in a QUESTION_AND_ANSWER format covering electric potential, potential energy, and related concepts from Chapter 25.

What is electric potential and how is it related to voltage?

Electric potential is the electric potential energy per unit charge; it is the quantity called voltage (1 V = 1 J/C).

What is electric potential energy U?

The energy required to move a charge against the electric field; the energy of the charge–field system; related to work done by conservative forces.

How do you express the potential difference ΔV between two points in an electric field?

ΔV = Vf − Vi = −∫i→f E · ds; in a uniform field this simplifies to ΔV = −E d for displacement d along the field.

What is the potential at a point?

The electric potential at a point is the potential energy per unit charge there; it is a property of the field (not the test charge).

What happens to potential energy when a positive charge moves with the field in a uniform field?

The potential energy decreases (ΔU < 0) and kinetic energy increases; the field does positive work on the charge.

What is an equipotential surface?

A surface where the electric potential has the same value everywhere; in a uniform field, equipotentials are planes perpendicular to the field.

What is the relation between electric field and electric potential?

E = −∇V; electric field lines point toward decreasing potential.

What are the units of voltage and electron-voltage?

1 V = 1 J/C; 1 eV = 1.602×10^−19 J; an energy change when a charge e moves through 1 volt.

What is the potential due to a single point charge q at distance r?

V = k q / r, where k = 1/(4πϵ0).

What is the potential energy for two point charges q1 and q2 separated by r?

U = k q1 q2 / r; for multiple charges, U = sum over all distinct pairs k qi qj / rij.

How is external work related to potential energy when moving a charge against the field?

Work by external agent Wext equals the increase in potential energy ΔU; the field does negative work Wfield = −ΔU.

What is a common reference for electric potential in problems?

V is often taken as zero at infinity: V∞ = 0.

What is ΔV in a uniform electric field for a displacement d along the field?

ΔV = − E d; the potential decreases in the direction of the field.

What is the potential difference between A and B in a uniform field?

ΔV = Vf − Vi = − ∫A→B E · ds = − E d along the field direction.

What can you say about equipotential lines for an infinite sheet of charge?

Equipotential lines are parallel to the sheet and perpendicular to field lines; the field is uniform and perpendicular to the sheet; E = σ/(2ε0) on each side.

What is the potential on the axis of a uniformly charged ring?

V on the axis a distance x from the center: V = k Q / √(a^2 + x^2).

What is the electric field on the axis of a uniformly charged ring?

E = k Q x / (a^2 + x^2)^(3/2), directed along the axis.

What is the superposition principle for electric potential from multiple point charges?

Total potential V at a point is the algebraic sum: V = ∑ k qi / ri.

What is the superposition principle for potential energy among multiple charges?

Total potential energy U is the sum of contributions from all charge pairs: U = ∑_{i<j} k qi qj / rij.

What did Millikan's oil-droplet experiment demonstrate about charge?

Charge on the electron is quantized: q = n e with e ≈ 1.60 × 10^−19 C; charge values occur in integer multiples of e.

What is a Van de Graaff generator?

A device that builds up very high voltages by moving a belt of insulating material to a high-voltage dome; can accelerate particles.

What is an electrostatic precipitator?

A device that removes particulate matter from gases by charging particles and collecting them on walls.

What is xerography?

A photocopying process using photoconductive materials that become conductive when illuminated, enabling toner transfer.

What is the relationship between equipotential surfaces and field lines?

Equipotential surfaces are everywhere perpendicular to electric field lines.

What is a conservative field’s key property regarding path independence?

In a conservative field, the line integral of E·ds between two points is path independent; ∮ E·ds = 0 for any closed loop.