Uses of Electromagnets

Overview

This lesson is about why electromagnets matter in real devices. The key idea is that an electromagnet can be switched on and off and its strength can be changed, which makes it more useful than a permanent magnet in many circuits.

What You Need to Know

• An electromagnet is made by passing current through a coil, often around a soft iron core.
• Its magnetic effect disappears when the current is switched off, so it can be controlled.
• In a relay, a small current in one circuit activates an electromagnet that closes or opens a switch in another circuit.
• Relays are useful when a low-current control circuit needs to operate a higher-current circuit.
• In a loudspeaker, a current-carrying coil in a magnetic field experiences forces that make the cone vibrate and produce sound.

How to Work Through It

1. Start by comparing permanent magnets and electromagnets so the advantage of switchable magnetism is clear.
2. Follow the stages in a relay and identify what happens in the control circuit and the output circuit.
3. Trace what happens inside a loudspeaker from changing current to cone vibration.
4. Finish with application questions where you choose the most suitable device for a given job.

Check Your Understanding

• Why is an electromagnet more useful than a permanent magnet in a relay?
• How can a small current be used to control a larger current safely?
• How does the magnetic effect of a current lead to sound in a loudspeaker?

Common Mistakes

• Treating a relay as if both circuits are the same circuit. The point is that one circuit controls another.
• Saying a loudspeaker works because the magnet pulls continuously in one direction. The current changes, so the force changes and the cone vibrates.
• Forgetting that the electromagnet stops working when the current stops.

Next Steps

• Use the lesson slides to rehearse the sequence of events in a relay and a loudspeaker.
• Keep the link between current, field, and force secure because the next lesson applies it to induction and generators.