S4.13.4 For the adult
Electric motors
A coil in a magnetic field is pushed at both sides. Why does it keep turning round and round, and not just flip over and stop?
What this chapter teaches
The forces on the two sides of a coil in a field are equal and opposite, so the coil turns. The turning effect falls to zero when the coil stands across the field. A split ring reverses the current at that moment, so the turn goes on the same way. A motor turns faster with a stronger magnet, more turns or a bigger current.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why do the two sides of the coil feel forces in opposite directions?
- What would happen to a coil with no split ring, and why?
- What are three ways to make a motor turn faster?
After the chapter, the learner can
- Explain how a split ring keeps a motor turning one way
- Name ways to make a motor turn faster
What they copy into their notebook
Opposite forces on the two sides turn the coil. The split ring reverses the current every half turn. Faster: stronger magnet, more turns, bigger current. Reverse the current or the magnet to reverse the turn.