Explain how the concept of a field allows physicists to describe the force experienced by a small positive charge placed near a large positive charge, and describe how the electric field lines in this region would be arranged.

AQA A-Level Physics (7408) — 3.7.1 Fields · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Electric fields exist around charged objects. A small positive test charge can be used to investigate the field.

Model answer (5 marks)

A field is a region of space where an object experiences a non‑contact force.
The electric field exerts a repulsive force on the small positive charge because both charges have the same sign.
The direction of the field line shows the direction of the force on a positive test charge.
The field lines point radially outward / away from the large positive charge.
The field lines are closer together (more dense) near the large charge, showing the field is stronger there.

Examiner tips

  • Use the definition of a field first, then explain the force direction, then describe the line pattern and density.

Common mistakes

  • Confusing attractive with repulsive force; describing lines pointing inward; omitting the density variation near the charge.

Mark scheme (5 marks)

  1. A field is a region of space where an object experiences a non-contact force
  2. The electric field exerts a (repulsive) force on the small positive charge because both charges have the same sign
  3. The direction of the field line shows the direction of the force on a positive test charge
  4. The field lines point radially outward / away from the large positive charge
  5. The field lines are closer together (more dense) near the large charge, showing the field is stronger there

Key terms in this question

electric field · field lines

Related

More Fields questions

▶ Try answering this question with AI marking (free) →