Paper 1 Q19 — Not every field gives a circle

Charged particles in fields — circular (magnetic) vs parabolic (electric) paths

What the examiners said

“Option B was the most common incorrect answer, where candidates thought that the protons would follow a circular path.”

Try the question (reconstruction)

A beam of protons travels horizontally into a region with a uniform electric field pointing vertically downward. What is the shape of each proton’s path in the field?

Examiner report: “Candidates thought protons in a uniform electric field would follow a circular path.”

Explore — electric vs magnetic: parabola vs circle

Fire the proton into an electric field (constant-direction force) or a magnetic field (force always perpendicular to velocity). Watch the two path shapes.

Field strength: 5

Rule of thumb: fixed-direction force (electric, gravity) → parabola; always-perpendicular force (magnetic) → circle.

Original reconstruction inspired by the misconceptions described in the Singapore-Cambridge GCE A-Level H2 Physics 9749 November 2023 Examiner Report. Not the actual examination question. For classroom exploration.

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