This common misconceptions covers Common Misconceptions within The Motor Effect for GCSE Physics. Revise The Motor Effect in Magnetism for GCSE Physics with 18 exam-style questions and 12 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 8 of 13 in this topic. Use this common misconceptions to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 8 of 13
Practice
18 questions
Recall
12 flashcards
⚠️ Common Misconceptions
Misconception 1: "Use the right hand for the motor effect"
Use the LEFT hand for motors (force on a current in a field). The RIGHT hand is used for generators (or the right-hand rule for field direction around a wire). Remember: LEFT for force on conductor (motors), RIGHT for induced current (generators).
Misconception 2: "The motor would work fine without the commutator"
Without the commutator, the coil would rotate 90° to the vertical position (where forces are equal and opposite), then stop — or oscillate back and forth. The commutator reverses current every half turn, keeping the forces always pushing in the same rotational direction for continuous spinning.
Misconception 3: "Force is greatest when current is parallel to the field"
The opposite is true. Force is MAXIMUM when the current is at 90° (perpendicular) to the field. When the current is parallel to the field, the force is ZERO. This is why the motor coil has zero force at the 90° position (coil plane parallel to field) and maximum force when the coil is horizontal.
Quick Check: State the three variables that affect the size of the force on a current-carrying wire in a magnetic field.
Force F = B × I × L, so the three variables are: (1) magnetic flux density B (strength of field), (2) current I (size of current through wire), (3) length L (length of wire in the magnetic field). Increasing any of these increases the force.