Question

What will happen to a compass needle when the compass is placed below a wire and a current is made to flow through the wire? Give a reason to justify your answer.

Answer 1

A convenient way of finding the direction of magnetic field associated with a current-carrying conductor is using the Right hand thumb rule.
Imagine that we are holding a current-carrying straight conductor in our right hand such that the thumb points towards the direction of current. Then our fingers will wrap around the conductor in the direction of the field lines of the magnetic field. This is known as the right-hand thumb rule.
Let us consider that a current through a horizontal power line flows in east to west direction. Applying the right-hand thumb rule, the direction of magnetic field at a point below the wire is from north to south. The direction of magnetic field at a point directly above the wire is from south to north.
Thus, when a magnetic compass is brought below the current carrying wire the compass needle show deflection in the north-south direction.