Question

A straight wire lying in a horizontal plane carries a current from north to south. What will be the direction of magnetic field at a point just underneath it?

• A. Towards north.
• B. Towards east.
• C. Towards west.
• D. Towards south.

Answer 1

The correct option is B Towards east.



When electric current flows through a conductor, it creates a magnetic field around it. The magnetic field lines form concentric circles around the conductor. The direction of the magnetic field is perpendicular to the wire and is in the direction of wrapped fingers of the right hand holding the conductor and the thumb pointing upwards indicates the direction of the current. The direction of the magnetic field can be deduced by holding the current carrying conductor in the right hand with the thumb extended it will be pointing in the direction of the current flow from north to south.
The position of the fingers laid across the conductor will now point in the direction of the magnetic lines of force as shown in the figure.
Hence, the direction of the magnetic field will be towards east, just beneath the conductor.
If the direction of the current flowing through the conductor is reversed, the right hand will need to be placed onto the other side of the conductor with the thumb pointing in the new direction of the current flow.