Electromagnetism
Moving charges create magnetic fields.
About this topic
A current in a wire creates a circular magnetic field around it, discovered by Ørsted in 1820. Coiling the wire into a solenoid concentrates the field, similar to a bar magnet, and an iron core strengthens it. The strength increases with current and the number of turns.
Ørsted noticed a compass needle twitch when he switched on a current nearby, which was the first link between electricity and magnetism. The right-hand grip rule gives the field direction: point your thumb along the conventional current and your fingers curl the way the field circles the wire.
Electromagnets can be switched on and off, so they are used in cranes that lift scrap cars, electric bells, relays, MRI scanners and maglev trains. Doubling the current or the number of turns roughly doubles the strength.
A typical error is to confuse the rule for a straight wire with that for a coil, where the thumb points along the field inside and the fingers show the current direction.
Key ideas
- Oersted's discovery
- A coil of wire becomes an electromagnet
- Strength grows with current and turns
Quick check
Use cases: where Electromagnetism helps
- Homework: review the key idea behind Electromagnetism before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Electromagnetism without notes.
- Visual learning: play with the interactive lab to see how Electromagnetism changes when you adjust its inputs.
- Teaching a friend: explain Electromagnetism 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 Electromagnetism?
Moving charges create magnetic fields.
What will I learn in Electromagnetism?
Oersted's discovery. A coil of wire becomes an electromagnet. Strength grows with current and turns.
Is Electromagnetism 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 Electromagnetism 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 Electromagnetism?
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.