When an electrical current moves through the wire, the compass turns to follow the direction of the magnetic field around the wire, rather than the magnetic field of the Earth.
Even though we can’t see them, magnetic fields circle around electrical currents, such as electrical wires and powerlines. An electrical current is a flow of electrons.
The greater the electrical current, the greater the magnetic field will be. Magnetic fields will pass through any barrier such as a wall but as you move further away from the electrical current, the magnetic field will decrease.
You can use the thumb and fingers of your right hand to find the direction of a magnetic field around a wire. The electrical current flows through the wire from the positive electrode to the negative electrode of the battery. 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.
A Danish scientist called Hans Christian Oersted first documented the magnetic field of an electrical current in 1820.
When a flow of electrical current produces a magnetic field, it is called an electromagnet. Electromagnets are important in electrical engines as they can be used to change electrical energy into mechanical energy.
Magnetic fields occur naturally around electricity such as static electricity (like rubbing a balloon on your hair). A bolt of lightening also has 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.
Find out how electricity creates a magnetic field. Guest writer Beth Askham shows you how.
Warning: This activity uses a craft knife; younger scientists need an adult do this part.
What you need
- Sixty centimetres of plastic coated copper wire
- A large paper cup
- A craft knife
- 6-volt battery
- A small compass
- A marking pen
What to do
- First have a play with your compass. Find magnetic north and see what happens when you face different directions with the compass.
- Scrape off around three centimetres of plastic from both ends of the copper wire using a craft knife. Make small hooks in the wire at the ends to help you hook the wire to the battery terminals.
- With a pen or skewer, poke a hole right in the middle of the cup’s base. Pull the wire through the hole until half the wire sticks out the bottom and half sticks out the top.
- Place the cup upside down on the table.
- Attach the wire coming out from underneath the cup’s rim to the battery’s positive (+) terminal.
- Place the compass on top of the upside-down cup, next to the wire.
- Attach the wire sticking from the top of the upside-down cup to the battery’s negative (-) terminal.
- When both wires are attached to the battery, an electrical current will run through the wire from the positive (+) to negative (-) terminal.
- What happens to the compass needle?
- Draw some arrows on the cup in the direction that the compass needle is pointing.
What you need Prepare your wires. Link up your circuit and wrap it around your compass.