Magnetic Effect of a current-carrying conductor

Magnetic Effect of a current-carrying conductor

Electric and magnetic fields occur naturally wherever there is electricity. Electric fields are produced by electrically charged objects. Magnetic fields are produced by magnets and by an electric current in a wire. The magnetic field produced by an electric current is put to practical use like electromagnets.

An electromagnet can be made by sending an electric current through a coil of wire wound around an iron core, the coil usually consists of several hundred turns of insulated copper wire.

When a current flows through the coil, it produces a magnetic field. If an iron core is placed inside the coil, a stronger magnetic field will be created.

The soft iron core becomes temporarily magnetized when the current is switched on. If loses its magnetism when the current is switched off. This effect is used in electric bells and buzzers, and in scrapyards for shifting metal scraps around.


Magnetic Field Pattern

A magnetic field can be represented by lines that show the shape of the field. Magnetic field lines which are close together represent a strong field. The field direction is defined as the direction indicated by a compass needle placed in the magnetic field.

A simple rule that can be used to determine the direction of the magnetic field around a current-carrying wire is the “right-hand grip rule”. With the thumb of a clenched right hand pointing in the direction of the conventional current, then the fingers indicate the direction of the magnetic field.

The right-hand grip rule can also be used to indicate the direction of the magnetic field around a coil. The right-hand grip rule for a solenoid, in this case, the thumb points towards the north pole of the magnetic field while the fingers indicate the direction of the current in the solenoid.








(The poles of a solenoid can also be determined by using the direction of current as seen from each end. South = current flows clockwise in the solenoid. North = current flows anticlockwise)


Magnetic Field Strength

A magnetic field exists whenever a current is present. When an electrical appliance is switched on, there is a magnetic field around it. The field strength increases with current. Thus, a stronger magnetic field exists near appliances which use a bigger current. However, the strength of the magnetic field decreases with distance from a current-carrying source.

Electric fields are shielded by most objects, such as walls, buildings and trees but magnetic fields are not. In spite of being buried in the ground, magnetic fields of power lines are still not eliminated.

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