Describe an activity to know the direction of magnetic field produced by a current-carrying straight conductor. Also show that direction of magnetic field is reversed on reversing the direction of current.

Explanation

To know the direction of magnetic field due to flow of current in a straight conductor let us prepare a series circuit consisting of a long straight copper wire PQ, a plug key and a battery [Fig. 13.17]. Place the straight wire over a compass needle such that the wire parallel to the direction of compass needle.

Apply plug in the key so that current begins to flow, the compass needle deflects due to magnetic field produced due to flow of current in straight conductor. If current in wire flows from north to south (as shown in Fig. (a)], the north pole of the compass needle is seen moving towards the east. It shows that a magnetic field is produced by a current-carrying straight conductor. Now reverse the connections of battery so that current flows in the copper wire from south to north We find that north pole of compass is now deflected towards west [Fig. (b)]. This shows that on reversing direction of current, the direction of magnetic field is also reversed.