What's new

Confuse a compass with electricity

By David Shaw, 9 July 2020

A compass will turn to follow the direction of the magnetic field.

By Beth Askham and David Shaw

Did you know that electricity and magnetism are closely related phenomena? In this activity, you’ll create a magnetic field using electricity and find that this can cause chaos for a compass!

Safety: This activity uses a sharp craft knife. Ask an adult to help.

You will need

• Small compass*
• 60 centimetres of plastic-coated copper wire
• Craft knife
• D cell battery
• Rubber band

* Note that compass apps on smartphones may not work.

What to do

1. First have a play with your compass. Find magnetic north and see what happens when you face different directions with the compass.
2. Ask an adult to help you scrape off about three centimetres of plastic from both ends of the copper wire using a craft knife.
3. Put the rubber band around the battery, so it goes over the top and bottom.
4. Tuck one end of the wire under the rubber band at the positive end of the battery (the end with the bump).
5. Tuck the other end of the wire under the rubber band at the negative end of the battery.
6. When both wires are attached to the battery, an electrical current will run through the wire from the positive (+) to negative (-) terminal.
7. Put the compass on the middle section of the wire, so the wire runs across the middle of the compass.
8. What happens to the compass needle? What happens when you put the wire on top of the compass instead of underneath?
9. Remember to disconnect the circuit when you’re done!

What’s happening?

Even though we can’t see them, magnetic fields circle around electrical currents, such those flowing through electrical wires. A compass will turn to follow the direction of the magnetic field around the wire, rather than the magnetic field of Earth.

In this activity, the electrical current flows through the wire from the positive electrode to the negative electrode of the battery.

To find the direction of a magnetic field use the right hand rule.

You can use the thumb and fingers of your right hand to find the direction of a magnetic field around a wire. If you wrap your right hand around the wire and point your thumb in the direction of the electrical flow, the magnetic field will be moving in the same way as your fingers are curled around the wire. The direction your fingertips point should match the result on your compass!

Real-life science

A bolt of lightning is also electricity with a magnetic field around it. Lightning can even magnetise the rock, soil or metal in the place where it strikes. This creates a magnetic oddity in a landscape that can be used to find out the strength of a past lightning strike.

For more stories and activities about electricity, grab a copy of Double Helix issue 41!