Physics, visually · Electricity & Magnetism · Concept 12
Electromagnet and Motor
How can a crane magnet switch its grip on and off, and how does electricity make a motor spin?
Current makes a magnet. A magnet pushes on a current. Put the two together and you get a motor, the heart of every drive in a factory.
- Electromagnet tab. Add turns and current: count how many clips it lifts. Then remove the iron core.
- Set the current to zero. What happens to the clips? An electromagnet can be switched off, a permanent magnet cannot.
- Motor tab. Raise the voltage and the speed climbs. Press Reverse: the motor turns the other way when current flips.
Current in a coil is a magnet you can switch. Current in a field feels a push: that is a motor.
A coil carrying current acts like a bar magnet, stronger with more turns, more current and an iron core. A wire carrying current in a magnetic field feels a force: F = B I L. A loop on a shaft gets pushed up on one side and down on the other, so it spins.
Contactors, relays and solenoid valves
A small current in a coil pulls an iron armature. That is how a PLC output switches a motor or opens a pneumatic valve.
Lifting magnets in steel yards
An electromagnet picks up scrap; cutting the current drops it. No moving jaws needed.
DC, servo and induction motors
Different designs, same rule: current in a magnetic field gives force, force at a radius gives torque.