1A current makes a field
When a current flows in a wire, a magnetic field forms round it in circles. Compasses near the wire swing round; switch off and they swing back.
magnetic field
Lesson 27.4 notes
Electromagnets and motors
Magnets made with electricity, making them stronger, what they're used for, and how motors turn.
2Coil it up
Wind the wire into a coil and the fields add up. The coil's field is like a bar magnet's, with a north and a south pole: it is an electromagnet.
coilelectromagnet
3Making it stronger
An electromagnet is stronger with more turns of wire, a bigger current, or an iron core inside the coil. Each change lets it lift more paperclips.
core
4Switch it off
Switch off the current and the electromagnet stops being a magnet, so the paperclips drop. A permanent magnet can't be switched off.
5Scrapyard cranes
A scrapyard crane has a huge electromagnet. Switched on, it lifts steel scrap; switched off, it lets go exactly where the crane driver wants.
6Electric bells
In an electric bell, the electromagnet pulls the hammer onto the gong. That breaks the circuit, so the hammer springs back, the circuit is made again, and it repeats.
7Electric motors
A coil carrying a current between the poles of a magnet feels a force that turns it: an electric motor. Reverse the current and it turns the other way.
motor
Explore: Electromagnet lab
Change the current, the number of turns and the core, and count the paperclips it lifts. Then build a motor and reverse it.
Common mistake: An electromagnet only works while current flows
Switch off the current and an electromagnet stops being a magnet at once. That is exactly what makes it useful: it can be switched on and off.
Remember
- A current in a wire makes a magnetic field round it. A coil of wire carrying a current is an electromagnet.
- More turns, more current or an iron core make an electromagnet stronger. Switch off the current and it stops being a magnet.
- A coil carrying a current in a magnet's field feels a force that turns it: that is how an electric motor works.
Going further at GCSE