When current flows through a wire, it creates its own circular magnetic field around the wire. When this is placed inside an external magnetic field (e.g. between the poles of a magnet), the two fields interact.
On one side of the wire, the two fields point in the same direction and REINFORCE each other — creating a stronger field. On the other side, they point in opposite directions and CANCEL — creating a weaker field.
This asymmetry — strong field on one side, weak on the other — creates a net force pushing the wire from the stronger-field side toward the weaker-field side.
Catapult analogy: Imagine the magnetic field as a stretched elastic sheet. On the strong side, the field is "compressed" between the two sources — it pushes the wire out like a catapult. This is why the motor effect is sometimes called the "catapult effect".
This how it works covers Why a Current-Carrying Wire in a Field Experiences a Force within The Motor Effect for GCSE Physics. Revise The Motor Effect in Magnetism for GCSE Physics with 19 exam-style questions and 12 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 5 of 12 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for The Motor Effect
What is the motor effect?
Explain how Fleming's left-hand rule is used to find the direction of the force on a current-carrying conductor in a magnetic field.