State the general relation between E and V.

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

How does V vary with r for a point charge, and how does E?

V is proportional to 1/r; E is proportional to 1/r².

What is an equipotential?

A line or surface where every point is at the same potential.

What does the electric field look like between parallel plates?

Uniform: parallel, equally spaced field lines, with equally spaced parallel equipotentials.

What do equipotentials look like around a point charge?

Concentric circles (spheres) that are further apart at greater distances.

How much work is done moving a charge along an equipotential?

None, because the potential difference is zero.

Electric potential and field patternsEdexcel International 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 test charge from infinity to that point.
State the equation for the field in a uniform field between plates.: E = V/d.
State the general relation between E and V.: E = −ΔV/Δx: the field strength is the negative of the potential gradient.
State the potential of a point charge.: V = Q/(4πε0r).
Is electric potential a vector or a scalar?: A scalar.
How does V vary with r for a point charge, and how does E?: V is proportional to 1/r; E is proportional to 1/r².
What is the work done moving a charge Q through a potential difference ΔV?: W = QΔV.
What is an equipotential?: A line or surface where every point is at the same potential.
What angle do equipotentials make with field lines?: Right angles.
What does the electric field look like between parallel plates?: Uniform: parallel, equally spaced field lines, with equally spaced parallel equipotentials.
What do equipotentials look like around a point charge?: Concentric circles (spheres) that are further apart at greater distances.
How much work is done moving a charge along an equipotential?: None, because the potential difference is zero.

Exam questions on Electric potential and field patterns

Two large, flat, parallel metal plates are 4.0 cm apart in a vacuum. A potential difference of 600 V is maintained between them, with the upper plate positive.
A proton is placed in the field between the plates. Calculate the force on the proton and state its direction. (Charge of a proton = 1.60 × 10⁻¹⁹ C.)2 marks
An isolated small sphere carries a charge of +8.0 nC in a vacuum. Its charge may be treated as a point charge at its centre.
Calculate the work done by an external force in moving a +2.0 nC charge slowly from 0.40 m to 0.20 m from the centre of the sphere.2 marks
Along a straight line in a region of electric field, the potential falls uniformly from 240 V at a point X to 80 V at a point Y. The distance XY is 0.040 m.
Calculate the electric field strength between X and Y, assuming it is uniform, and state its direction.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).