IGCSE Physics: DC Motors and Loudspeakers | Magnetism & Electromagnetism | Unit 7 | L6

This lesson covers spec point 7.12 (applied) of the Edexcel Modular IGCSE Physics specification — the structure and operation of a simple DC
motor and a loudspeaker as applications of the motor effect.

PowerPoint includes:
• Retrieval starter reviewing Fleming’s left-hand rule and the motor effect from L5
• Direct Instruction (I Do) — DC motor components introduced: current-carrying coil, permanent
magnet, split-ring commutator, carbon brushes; the role of the commutator explained in
terms of maintaining rotation by reversing current direction every half turn; loudspeaker
structure introduced: permanent magnet, coil attached to cone; the link to the motor effect
explained — alternating current in the coil produces alternating force, which drives the
cone forwards and backwards, creating pressure waves; the effect of frequency and amplitude
on the sound produced
• Guided Practice (We Do) — three questions: describe the role of the commutator; explain
why a loudspeaker cone moves when a current flows; predict what happens to the sound if the
frequency of the AC signal doubles
• Check for Understanding — 3 MCQs on commutator function, loudspeaker operation and energy
transfers
• Independent Practice (You Do) — activity sheet with exam-style questions
• Review and Reflect — exit ticket on energy transfers in a DC motor

Activity Sheet includes:
• 10 questions (20 marks) progressing from describing components through to explaining
the commutator’s role, the effect of frequency and amplitude on loudspeaker output,
comparing energy transfers in motors and loudspeakers
• Stretch question asking students to evaluate whether a DC motor could be run in reverse
to act as a generator, linking forward to electromagnetic induction in L7
• Full mark scheme for teacher use