Electromagnets
When there is a current in a wire, a circular Area surrounding a magnet that can exert a force on magnetic materials. is produced around the wire. This magnetic field can To cause something to change direction. the needle of a magnetic compass. The strength of the magnetic field is greater:
- closer to the wire
- if the current is increased
Solenoids
A A straight coil of wire which can carry an electric current to create a magnetic field. is a long coil of wire. When a direct electric current is passed through it, the shape of the magnetic field is very similar to the field of a bar magnet. The field inside a solenoid is strong and uniform. The small magnetic fields caused by the current in each turn of the coil add together to make a stronger overall magnetic field.
The strength of the magnetic field around a solenoid can be increased by:
- increasing the number of turns on the coil
- increasing the current
- placing an iron core inside the solenoid
The use of an iron core makes the solenoid into an A magnet made by wrapping a coil of wire around an iron bar and passing an electric current through the coil. which can be switched on and off.