Electric potential can be zero at a point where the electric field is nonzero. Potential adds as a signed scalar. The field adds as a vector. At the midpoint of equal and opposite point charges, the two potential contributions cancel and the two field contributions point the same way.
The 2027 A-Level H2 Physics syllabus (9478) includes electric potential, electric fields and their relationship through the potential gradient. This worked example lets you check the sign and direction separately.
- Use the signed charge when adding electric potentials.
- Find each field’s direction before adding its magnitude.
- Check the slope of potential when explaining the net field.
Worked example | The midpoint between +2.0 nC and −2.0 nC
Place +2.0 nC at x = −0.10 m and −2.0 nC at x = +0.10 m. With potential taken as zero at infinity and k ≈ 9.0 × 10⁹ N m²/C², the potentials at the midpoint are +180 V and −180 V. Their sum is zero.
Each field has magnitude k|Q|/r² = 1,800 N/C at the midpoint. The positive charge produces a field pointing away from itself, towards the right. The negative charge produces a field pointing towards itself, also towards the right.
The net field is 3,600 N/C to the right. A small positive test charge placed at that point would experience a force to the right even though its electric potential energy relative to infinity would be zero there.
Explain the result using the potential gradient
Move slightly to the right along the line between the charges. The distance to the positive charge increases and the distance to the negative charge decreases. The positive contribution falls and the negative contribution becomes more negative. Total potential decreases as x increases.
The electric field component is minus the potential gradient. A falling potential along x gives a positive field component. A potential value of zero at one point says nothing on its own about the slope there.
Replace the negative charge with a positive charge
Both midpoint potentials are now +180 V, giving +360 V. The two fields point in opposite directions and have equal magnitudes, so the net field is zero at the midpoint.
Ask a study partner to predict the potential first and the field second. If either answer relies on a cancellation, name exactly what cancels and why.
Frequently asked questions
Is an equipotential surface a region with no electric field?
The field has no component tangent to that surface. It may have a nonzero component perpendicular to it.
Which way would an electron accelerate at the original midpoint?
Its negative charge gives a force opposite to the field, towards the left in the example.
Official information
SEAB’s 2027 A-Level H2 Physics syllabus (9478), Electric Field and Electric Potential. Checked 10 November 2026.