School › Magnetism › Ages 10–11
Magnetism: poles, fields and electromagnets
Magnetic materials, poles, magnetic fields, Earth's own magnetism and how electricity makes magnets. With a build-an-electromagnet experiment.
Read
Only a few materials are strongly magnetic: iron, nickel and cobalt (and a rare metal called gadolinium). Steel, which is mostly iron, is magnetic too. Most other materials, such as plastic, wood, copper and aluminium, are not.[2]
Every magnet has a north pole and a south pole. Like poles repel (push apart) and unlike poles attract (pull together). If you cut a magnet in half, you do not get a separate north and south: you get two smaller magnets, each with both poles.[1]
The Earth acts like a giant bar magnet. A compass needle is a small magnet that lines up with Earth's magnetism, so its north end points north. Most of Earth's magnetism is made deep inside the planet, where liquid iron and nickel churn in the outer core.[1][3]
Earth's magnetism stretches far into space, forming a protective bubble called the magnetosphere. It shields our atmosphere from the solar wind, a stream of particles from the Sun. Near the poles, energetic particles from the magnetosphere make the air glow: the northern and southern lights (auroras).[3]
Electricity and magnetism are linked: an electric current makes a magnetic field. A coil of wire carrying a current becomes a magnet that you can switch on and off, an electromagnet. An iron core inside the coil makes it much stronger. Electromagnets are used in cranes, doorbells and loudspeakers.[2]
Try it: Build an electromagnet
You need
- A large iron nail (about 8–10 cm)
- About 1.5 m of thin insulated copper wire
- A 1.5 V battery (AA or D) and some tape
- A pile of small steel paper clips
Safety
Use only one 1.5 V battery. Connect for a few seconds at a time: the wire and battery get warm. Never connect to a mains socket.
What to do
- Leave about 20 cm of wire free, then wrap 10 turns of wire tightly around the nail. Strip the insulation from the wire ends (an adult helps).
- Tape the wire ends to the two ends of the battery for a few seconds only.
- While connected, touch the nail tip to the paper clips. Count how many it picks up.
- Disconnect. What happens to the paper clips?
- Now wrap 20 turns, then 30 turns, and count the paper clips each time. Keep the battery the same.
What happens, and why?
The current in the coil makes a magnetic field, and the iron nail inside makes it much stronger, so the nail becomes a magnet. When the current stops, the nail loses most of its magnetism and the clips drop. More turns of wire give a stronger magnet, so it lifts more clips. This is a fair test because only the number of turns changes.[2]
Play: Attract, repel or nothing?
Two things are brought close together. Do they attract, repel or do nothing?
Your best score is kept only on this device. Nothing is sent anywhere.
Quiz
Other ages: Ages 6–7 · Ages 15–16