Who this is for: Cambridge IGCSE Coordinated Science (0654) students who want the d.c. motor — construction, split-ring commutator and turning effect — to become a reliable source of marks instead of a labelled diagram they cannot explain.
What query it owns: how to understand and revise the d.c. motor in Cambridge IGCSE Coordinated Science.
Why this is safe: this page owns the d.c. motor revision-guide angle, while Tutopiya’s D.C. Motor subtopic page owns the learning resource and the free D.C. Motor quiz owns the practice.

A d.c. motor converts electrical energy into kinetic energy using the motor effect. Cambridge IGCSE Coordinated Science (0654) expects you to label the coil, magnets, brushes and split-ring commutator, explain how the commutator keeps rotation in one direction, and state factors that increase turning effect. This guide links each part to the description and explanation questions examiners set.

Key takeaways

• A d.c. motor uses the force on a current-carrying coil in a magnetic field.
• The split-ring commutator reverses current direction in the coil every half turn.
• This keeps the turning effect (torque) in the same rotational direction.
• Brushes maintain electrical contact with the rotating commutator.
• Turning effect increases with current, number of turns and magnetic field strength.

What is a d.c. motor in Cambridge IGCSE Coordinated Science?

A coil of wire sits between the poles of a permanent magnet. When current flows through the coil, opposite sides experience forces in opposite directions (Fleming’s left-hand rule), creating a turning effect. Without a commutator, the coil would swing back after half a turn. The split-ring commutator swaps the connections every half turn so the force direction on each side stays consistent, producing continuous rotation.

You can read the full explanation, diagrams and notes on Tutopiya’s D.C. Motor subtopic page before you attempt questions.

Key parts of a d.c. motor

Part	Function
Coil (armature)	Carries current; experiences the motor effect force
Permanent magnets	Provide the magnetic field
Split-ring commutator	Reverses current in the coil every half turn
Brushes	Sliding contacts connecting power supply to commutator
Axle	Transfers rotation to the load (e.g. fan blade)

Factor	Effect on turning effect
Current ↑	Stronger turning effect
Number of coil turns ↑	Stronger turning effect
Stronger magnetic field	Stronger turning effect
More coils (poles)	Smoother rotation

D.C. motor in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical d.c. motor stem
Describe	How it works, step by step	”Describe the function of the split-ring commutator.”
Explain	Reason using physics	”Explain why the coil continues to rotate in the same direction.”
State	Name a part or fact	”State the energy transfer in a d.c. motor.”
Suggest	Apply knowledge	”Suggest how to increase the speed of the motor.”

Worked exam-style stems (how to answer the wording)

1. “Describe the function of the split-ring commutator in a d.c. motor.” It reverses the direction of current in the coil every half turn, so the force on each side of the coil always acts in the same rotational direction. Mark-scheme reward: reverses current every half turn + keeps rotation continuous.
2. “State the energy transfer that takes place in a d.c. motor.” Electrical energy → kinetic energy (of the rotating coil/axle). Reward: correct input and output energy forms.
3. “Explain why the coil would not rotate continuously without a commutator.” After half a turn the forces would reverse direction, pulling the coil back — it would oscillate rather than rotate fully. Reward: forces reverse without commutator.

Test yourself with the D.C. Motor quiz once you can label the parts and explain the commutator’s role.

How the d.c. motor connects to the rest of Coordinated Science physics

The d.c. motor builds on Force On A Current Carrying Conductor and Magnetic Effect of an Electric Current, and leads into Electromagnetic Induction (the reverse process). The Cambridge IGCSE Coordinated Science resource hub links every Electromagnetic Effects subtopic.

Common mistakes students make

• Confusing the split-ring commutator (d.c. motor) with a slip ring (a.c. generator).
• Saying the commutator stops current reversal (it causes reversal at the right moment).
• Forgetting that energy transfer is electrical → kinetic (not the other way around).
• Not explaining why the commutator is needed (forces would reverse without it).
• Mixing up brushes (stationary contacts) with the commutator (rotating rings).

When you need more support

If d.c. motor questions keep costing marks, work through the D.C. Motor quiz, then get focused help from a Cambridge IGCSE Coordinated Science tutor.

Frequently asked questions

Is the d.c. motor hard in Coordinated Science? Learn the key parts, what the commutator does and the energy transfer — that covers most questions.

What does the split-ring commutator do? It reverses the current in the coil every half turn so the coil keeps rotating in the same direction.

What energy transfer occurs in a d.c. motor? Electrical energy from the supply is converted to kinetic energy of the rotating coil and axle.

How do I revise the d.c. motor effectively? Practise labelled diagrams, commutator explanations and speed-increase suggestions, then take the D.C. Motor quiz.

Ready to master Cambridge IGCSE Coordinated Science d.c. motors?

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