Magnetic Field due to Current Carrying Wire

Magnetic Field due to Current Carrying Wire

Straight wire :

It means that when the current flows in a straight wire, the magnetic field produced has circular lines of force surrounding the wire, having their centres at the wire as shown in fig. The plane of circular lines is perpendicular to the length of the wire. Their direction is marked by arrows.

Straight wire
Straight wire

   Current straight, magnetic field circular

Circular coil 

Current circular, magnetic field straight
Current circular, magnetic field straight

It means that when the current flows in a circular wire (coil), the magnetic field produced has straight lines of force near the centre of the coil, as shown in figure. The parallel lines are in a plane perpendicular to the plane of the coil. Their direction is marked by the arrows.

Rule : The direction of the magnetic lines of force is related with the direction of the current by the right hand thumb rule.

The rule states :

Curl the four fingers of the right hand on the palm, keeping the thumb stretched out at right angles. The thumb is straight and the fingers are circular.

In case 1. thumb represents the direction of the current in the straight wire and curling of fingers represents the direction of the circular magnetic lines of force (fig.).

 

magnetic effect of current
magnetic effect of current

In case 2, curled fingers represents the direction of the current in circular wire and thumb represents the direction of the straight magnetic lines of force. (Fig.)

Right hand thumb rule for direction of magnetic field.

Solenoid

Definition : A solenoid is a straight cylindrical core on which a large number of turns of a insulated copper wire are wrapped. It is shown in fig.

 

Solenoid
Solenoid

 

Solenoid carrying a current and polarity of its face