Physics › Section P · Magnetism › Topic P.4
Torque on a current loop: motors and meters
Put a loop of current in a magnetic field and the forces on its sides do not push it anywhere: they twist it. That twist turns every electric motor, from a phone's vibration buzzer to a train, and swings the needle of an analogue meter.
In this topic
- From a straight wire to a loop
- Finding the torque
- The torque equation
- Maximum, zero and reversed torque
- Worked example: torque on a motor coil
- Keeping a motor turning
- Analogue meters
- Worked example: a galvanometer's spring
- Common mistakes to avoid
- Key takeaways
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