Science 8th grade
UNIT 13: Magnetism 13.6 Electric currents make Magnetic field
Science 8th grade
UNIT 13: Magnetism 13.6 Electric currents make Magnetic field
An electric current must flow through an electromagnet if the magnet is to work. The current makes the magnetic field.
The field of an electromagnet
The magnetic field of an electromagnet is like the field of a bar magnet.
• The magnetic field lines come out of one end of the electromagnet. This is its north pole.
• The field lines go round and back into the other end of the electromagnet. This is its south pole.
Activity 13.6A (The field of an electromagnet)
SE: Use iron filings or small compasses to investigate the magnetic field of an electromagnet.
Safety! Take care to avoid getting iron filings on your hands as you might rub them into your eyes.
Here is a question to investigate: Is the field of an electromagnet different when it has an iron core?
Question
1) Draw a diagram of an electromagnet. Add magnetic field lines. Mark the places where the magnetic field is strongest.
Current and field
Hans Christian Oersted was a Danish scientist. He thought that there might be a connection between clectricity and magnetism.
One day, in 1820, he was giving a lecture about electric circuits. A magnetic compass was lying nearby on the bench. When he switched on his circuit, he noticed that the compass needle changed direction.
Oersted had discovered that whenever an electric current flows in a wire it makes a magnetic field around it. The photograph shows a modern version of his experiment.
When the switch is closed, the battery makes a current flow in the wire. The compass needle moves round, just as in Oersted's experiment.
Activity 13.6B (Oersted's experiment)
SE: Set up an electric circuit like the one shown in the photograph. Place a plotting compass under the wire. Does the needle move when you switch the circuit on?
Find out what happens if you swap the connections to the battery, so that the current flows in the opposite direction.
Find out what happens if you place the compass in different positions.
How an electromagnet works
The magnetic field around a wire is quite weak. An electromagnet is a clever ide because, by winding the wire into a coil, you concentrate the magnetic field into smaller space, making it much stronger.
Question
2) The diagram shows the magnetic field around a wire when a current flows in the wire.
a: What shape are the magnetic field lines?
b: Where is the magnetic field strongest? Explain how you can tell from the diagram.
The magnetic field around a wire with an electric current flowing in it.