Is electric potential a vector or a scalar?

A scalar. Potentials add as numbers, with their signs.

State the relation between field strength and potential.

E = −ΔV/Δx: the field is the negative of the potential gradient.

Which way does an electric field point relative to the potential?

In the direction in which the potential decreases.

Describe the field lines in a uniform field.

Parallel and equally spaced, at right angles to the plates.

Describe the equipotentials in a uniform field.

Equally spaced planes parallel to the plates, at right angles to the field lines.

What are the equipotentials around a point charge?

Concentric spheres, drawn as circles, at right angles to the radial field lines.

Why is no work done moving a charge along an equipotential?

There is no change in potential, so no change in potential energy.

Can the potential be zero where the field is not?

Yes. The field depends on the potential gradient, not the value, for example at the midpoint between equal and opposite charges.

Electric potential and field patternsEdexcel A-Level Physics: Flashcards

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Define electric potential at a point.

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Define electric potential at a point.: The work done per unit positive charge in bringing a small positive test charge from infinity to that point.
Is electric potential a vector or a scalar?: A scalar. Potentials add as numbers, with their signs.
What is the potential at infinity?: Zero.
State the relation between field strength and potential.: E = −ΔV/Δx: the field is the negative of the potential gradient.
Which way does an electric field point relative to the potential?: In the direction in which the potential decreases.
State E for a uniform field between parallel plates.: E = V/d.
Describe the field lines in a uniform field.: Parallel and equally spaced, at right angles to the plates.
Describe the equipotentials in a uniform field.: Equally spaced planes parallel to the plates, at right angles to the field lines.
State the potential of a point charge Q at distance r.: V = Q/4πε₀r.
How does V vary with r for a point charge, and how does E vary?: V ∝ 1/r and E ∝ 1/r².
What are the equipotentials around a point charge?: Concentric spheres, drawn as circles, at right angles to the radial field lines.
Why is no work done moving a charge along an equipotential?: There is no change in potential, so no change in potential energy.
Can the potential be zero where the field is not?: Yes. The field depends on the potential gradient, not the value, for example at the midpoint between equal and opposite charges.

Exam questions on Electric potential and field patterns

Two large parallel metal plates are 0.040 m apart in a vacuum. A potential difference of 600 V is maintained across them. Away from the edges of the plates the field between them can be treated as uniform.
Calculate the electric field strength between the plates and the magnitude of the force on an electron in the field.2 marks
A small sphere carries a charge of +8.0 nC. It may be treated as a point charge in a vacuum. Point P is 0.30 m from the centre of the sphere.
Calculate the electric potential at P.2 marks
A tiny oil droplet of mass 2.6 × 10⁻¹⁵ kg carries a negative charge. It is held at rest between two horizontal parallel plates, 15 mm apart, by a potential difference of 480 V across the plates.
Calculate the electric field strength between the plates and state which plate is at the higher potential.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).