Electromagnetic Induction
A changing magnetic field induces voltage.
About this topic
Faraday discovered that a changing magnetic flux through a circuit induces an EMF: ε = −N ΔΦ/Δt. Moving a magnet in and out of a coil, or rotating a coil in a field, induces a voltage; faster change or more turns produces more. Lenz's law says the induced current opposes the change that caused it.
Push a north pole into a coil and the coil creates its own north pole facing the magnet to resist it, so you must do work; that work becomes the electrical energy, in line with conservation of energy. Drop a magnet down a copper tube and it falls slowly because of induced currents.
This principle underlies generators, transformers, induction cooktops, wireless phone charging, guitar pickups and the braking systems of some trains.
Students often think a magnet sitting still in a coil induces a voltage. It is the change in flux that matters, so you need relative motion or a changing current. The minus sign in the formula expresses Lenz's law and conservation of energy.
Key ideas
- Faraday's law
- Lenz's law gives direction
- Generators and dynamos
Quick check
Use cases: where Electromagnetic Induction helps
- Homework: review the key idea behind Electromagnetic Induction before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Electromagnetic Induction without notes.
- Visual learning: play with the interactive lab to see how Electromagnetic Induction changes when you adjust its inputs.
- Teaching a friend: explain Electromagnetic Induction in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Electromagnetic Induction?
A changing magnetic field induces voltage.
What will I learn in Electromagnetic Induction?
Faraday's law. Lenz's law gives direction. Generators and dynamos.
Is Electromagnetic Induction part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Electromagnetic Induction lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Electromagnetic Induction?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.