Paper 1 Q2 — Dipole rotation and centre of mass

Dipole in a field — alignment for maximum rotational KE; centre of mass position

What the examiners said

“Only a minority realising that the centre of mass would be closer to the oxygen atom… some suggested it would be antiparallel with the field… only the stronger responses also used the correct range of angles” for the rotational kinetic energy.

Try the question (reconstruction)

A polar molecule (a permanent dipole) is released at an angle in a uniform electric field. At what orientation is its rotational kinetic energy a maximum?

Examiner report: “Some wrongly said the dipole reaches maximum KE antiparallel to the field.”

Explore — torque, alignment and energy

Release the dipole at an angle. It rotates toward alignment with the field, gaining rotational KE, then overshoots and oscillates. Watch KE peak at the aligned position.

Release angle (°): 120

Aligned = lowest PE = highest KE (stable). Antiparallel = highest PE = lowest KE (unstable). The dipole oscillates about the aligned position.

Original reconstruction inspired by the misconceptions described in the Singapore-Cambridge GCE A-Level H3 Physics 9814 November 2023 Examiner Report. Not the actual examination question. For classroom exploration.

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