Magnetic Effects of Electric Currents

The magnetic effect of an electric current.

When an electric current passes through a wire, a magnetic field is produced around the wire. If the wire is wound into a coil the resulting field is similar to that of a bar magnet wit north and south poles.

Predicting the direction of the field around a current carrying conductor.

Maxwell’s screw rule:Imagine that a right handed screw

is turned so that it moves forward in the direction of convectional current. Then, its direction of rotation indicates the direction of the magnetic field due to the current.

Predicting the direction of the field around a current carrying

conductor.You can also use the right hand grip

rule, which says:If a conductor carrying a current is

gripped with the right hand, with the thumb pointing along the conductor in the direction of conventional current, the curl of the fingers around the conductor indicates the direction of the magnetic lines of force.

Electromagnets An electromagnet is a temporary

magnet which has magnetism only when current is passing through a coil wire. The strength of the magnetic field associated with an electromagnet can be increased by

• Increasing the current• Increasing the number of turns pf coil

per length• Including a soft iron core.

Applications of electromagnets• To lift iron rods and steel bars.• As cranes in scrap yards• In hospitals to remove splinters

from eyes.• In electric bells• In the cores of transmissions• In control systems.

The magnetic RelayThe basic relay consists of a coil

and a set of contacts. When voltage is applied to the coil, current passes through the wire and creates a magnetic filed. The magnetic field pulls the contacts together and hold them there until the current flow is stopped.

Magnetic Relay

The force on a current carrying conductor in a magnetic field.

The direction of the force which results from the interaction of a current and a magnetic field can be predicted by’ Fleming's Left Hand Rule’.

Fleming's Left Hand Rule.

• The first finger is the direction of the field

• The second finger is the direction of current.

• Thumb is the movement of the wire.

A current carrying conductor in a magnetic

field.• Above the conductor, the field of

the conductor and that of the magnet are acting in the same direction. The field is strengthened.

• Below the conductor, the field of the conductor and that of the magnet ar in the opposition. The field is weakened.

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