Electromagnetism

• When current passes through a wire,a magnetic field is produced around the wire.
• The wire is said to have magnetised.
• This magnetic effect is called electromagnetism.
• The magnetic field lines form concentric circles around the wire.
• If a compass is placed near the wire, the magnetic field can cause the compass needle to deflect.
• A larger current in the wire will produce a stronger magnetic field.
• The magnetic field lines in a stronger magnetic field will be closer together.
• In a stronger magnetic field, the deflection of the compass needle will be greater.

Right-Hand Grip Rule

• To predict the direction of magnetic current around a wire, the right-hand grip rule is used.
• To use this rule, grip the wire with the right hand.
• The thumb should be pointing along the direction of the current.
• The fingers will point to the direction of the magnetic field around the wire.

Electromagnets

• An electromagnet is a magnet produced by the flow of electric current.
• It loses its magnetism when the current stops flowing.
• A coil of wire, or solenoid, carrying electric current can also show magnetic properties.
• The magnetic field lines around the coil are similar to the field lines around a bar magnet.
• The strength of an electromagnet can be increased by
• (a) increasing the number of turns of the coil
• (b) increasing the amount of current flowing through the coil
• (c) inserting a soft iron core into the coil.
• Electromagnets are used in many devices such as electric bells, microphones, telephones, loudspeakers, in cranes at dockyards and steelworks, and in hospitals to remove iron or steel splinters from our body.