A magnetic field is created when an electric current flows through a wire. The direction of the magnetic field depends on the direction of the current flowing through the wire.
The right-hand thumb rule helps us know the direction that the current flows.
The arrows in the diagram above show the direction of the magnetic field. But instead of a straight line, it would be a coil of wire. As the distance from the wire increases, the circles (magnetic field lines) get further apart.
When current is flowing through a coil of wire, the magnetic field will look similar to the magnetic field of a bar magnet. If we place a compass near the wire, we will see that it traces the direction of the magnetic field. We can represent the magnetic field with magnetic field lines.
Here we have a solenoid, which is a coil of insulated wire. It produces a magnetic field that flows out of the north and into the south. The field lines are concentric circles around the wire. They are closer together near the wires because that is where the magnetic field is strongest.
When looking to understand electromagnetism, we can break the word electromagnet can be split into two parts. ‘Electro‘ relates to electricity and ‘magnet‘ relates to magnetism. An electromagnet is a solenoid wrapped around an iron core.
The diagram below shows a simple electromagnet, with the coil wrapped around an iron nail.
Once you turn on the power supply and there is current flowing through the wire, a magnetic field will be produced. When you turn off an electromagnet, it loses its magnetism. This makes it useful for moving magnetic objects, by picking them up and dropping them off in different places.
We may want to make the strength of the magnetic field around the solenoid, and we can do this in three different ways:
1. Wrapping the coil around an iron core
2. Increasing the flow of current through the coil
3. Increasing the number of turns of the coil.
1. When the button is pressed, current flows through the electromagnet.
2. The electromagnet attracts the iron armature, which causes the hammer to hit the bell.
3. The armature moving breaks the circuit, which stops the current and destroys the magnetic field.
4. As the current stops, the armature moves back to its original position, reconnecting the circuit.
5. The electromagnet turns back on and the whole process starts again.