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A2 Daily A Level Physics question

2026-05-17 OCR A Electric fields: potential & equipotentials (M6) OCR-A M6.2 Electric fields: uniform fields and potential difference OCR-A M6.2.2 Equipotential lines/surfaces and work done moving a charge (qualitative)

In a lab, two large parallel metal plates are connected to a power supply, creating a uniform electric field between them. A small positive test charge is moved very slowly by an external force along a path that lies entirely on an equipotential line (start and end at the same potential). Which statement must be true about this move?

  1. A A The electric field at the charge is zero everywhere along the path.
  2. B B The electric field does no work on the charge over the move. (correct)
  3. C C The potential energy of the charge decreases as it moves toward the negative plate.
  4. D D The force on the charge is zero throughout because it stays on an equipotential.

Answer

The correct answer is B.

Correct: B — B The electric field does no work on the charge over the move. A The field need not be zero on an equipotential; equipotentials are perpendicular to non-zero field lines. B This is correct because start and end have the same potential, so the field transfers no energy to the charge. C Incorrect: with no change in potential, the electric potential energy of the charge does not decrease. D Incorrect: the field can still exert a force; the external agent supplies an equal and opposite force to constrain the path.

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