Networks, Time and Fields
Magnetism & Motors
13 minStudent plan
How current makes a magnetic field, how that field makes a motor turn, and why an inductive load will destroy your transistor if you let it.
After this lesson you can
- Explain how a current in a magnetic field produces force
- Say why a motor needs a driver and not an Arduino pin
- Explain what a flyback diode is protecting
Current makes a field
Every current produces a magnetic field around it. In a straight wire the field forms circles around the wire; wind that wire into a coil and the fields inside reinforce into a strong, roughly uniform field along the coil's axis. Add an iron core and it multiplies again.
The field strength rises with current and with the number of turns, which is why an electromagnet is specified in ampere-turns rather than either alone. A hundred turns at 0.1 A produces the same field as ten turns at 1 A.
This is the basis of relays, solenoids, speakers and motors, every one of them is a coil converting current into force.
In the full lesson
- Current makes a field
- Force, and why a motor spins
- Induction, and the flyback diode
This lesson comes with the Student plan. The first module of Physics for Engineers is free.