H1 Physics 8867 · Nov 2023PhysicsPaper 1Commented

Paper 1 Q23 — Field direction, not just magnitude

Electric fields — direction of E is the direction a positive test charge would move

What the examiners said

“…candidates can calculate electric field strengths but do not always understand that their direction is that in which a positive charge would move when placed in the field.”

Try the question (reconstruction)

A point charge of −4.0 nC is fixed at a point. P is 0.30 m to the right of the charge. What is the electric field at P?

Examiner report: “Candidates calculated field strengths correctly but chose the direction a negative or arbitrary charge would move.”

Explore — release a test charge

Flip the sign of the source charge and move point P around it. The arrow is the field at P. Press release to drop a small positive test charge at P and watch which way it accelerates — that is the field direction, by definition.

Source charge: −4.0 nC Distance r (m): 0.30 Angle of P (°): 0

With a negative source the test charge falls inwards — the field points towards the charge. Flip the sign: same magnitude everywhere, every arrow reverses.

Original reconstruction inspired by the misconceptions described in the Singapore-Cambridge GCE A-Level H1 Physics 8867 November 2023 Examiner Report. Not the actual examination question. For classroom exploration.

Made by lookang, using Claude Fable 5. More resources: iwant2study.org