Electromagnetism
Switch on a current and watch compass needles swing around the wire, then push a magnet through a coil to make electricity.
Standards: HS-PS2-5
1Wonder
In 1820, Hans Christian Ørsted noticed that a compass needle jumped every time he switched on an electric current nearby. Electricity and magnetism turned out to be two sides of one thing, and that discovery led to motors, generators and every power plant on Earth.
2Explore
This activity needs a bigger screen
Turn your phone sideways, or open this lesson on a tablet or computer. The explanation and quiz below work here.
- Set the current to 0. Which way do all the compass needles point? Now turn the current up.
- Make the current negative (into the screen). What happens to the needles?
- Which needles turn the most: the ones close to the wire or the far ones?
- Choose Magnet and coil. Push the magnet into the coil, then hold it still. When does the meter move?
- Pull the magnet out again, then try more turns. What changes?
3Explain
Currents make magnetic fields
Put a compass under a wire. With no current it points north. Switch the current on and the needle swings across the wire: a current makes a magnetic field.
A current makes a magnetic field that circles the wire. A changing magnetic field through a coil makes a voltage, bigger with more turns and faster change.
4Practice
What does an electric current in a wire make around it?
5Recap
- An electric current makes a magnetic field that circles the wire (right-hand rule).
- The field is stronger with more current and weaker farther away: B = μ₀I / (2πr).
- A coil makes an electromagnet you can switch on and off.
- A changing magnetic field through a coil induces a voltage: that is how generators work.