Transformers & Eddy currents

Overview

This lesson connects induction to devices and applications. You will use flux linkage and Lenz’s law to explain transformers and eddy currents, while also revising magnetic fields produced by currents in wires, coils, and solenoids.

What You Need to Know

• An alternating current in a primary coil produces a changing magnetic flux.
• A changing flux linkage in a secondary coil induces an e.m.f.
• A ferrous core increases and guides the magnetic field through the coils.
• Eddy currents are circulating induced currents in bulk conductors.
• Eddy currents can cause heating, damping, and magnetic braking.
• Lenz’s law explains why eddy-current effects oppose the motion or change that produces them.
• Currents in wires, coils, and solenoids produce characteristic magnetic field patterns.

How to Work Through It

1. Sketch field patterns for a straight wire, circular coil, and solenoid.
2. Explain how a changing flux in one coil can induce an e.m.f. in another.
3. Use Lenz’s law to predict the effect of eddy currents in a conductor.
4. Compare useful and unwanted eddy-current effects.

Check Your Understanding

• Why does a transformer require changing flux linkage?
• What role does a ferrous core play?
• Why do eddy currents oppose the motion that produces them?
• Why do parallel current-carrying conductors exert forces on each other?

Common Mistakes

• Explaining transformers as if charge flows directly from primary to secondary.
• Forgetting that eddy currents need a changing flux through a conducting path.
• Saying eddy currents always waste energy; they can be useful in braking and damping.
• Sketching solenoid fields without showing the strong, near-uniform field inside.

Next Steps

• Use this lesson as the bridge between field patterns, induction laws, and applications.
• Bring all equation and direction work into the revision lesson.