Solution:

Experiment: A wire AB, running north-south, is linked to a battery through a rheostat and a tapping key in Figure. A compass needle is set just below the wire.
Observations:
(1) When the key is open, the needle exhibits no deflection, indicating that no current is flowing through the wire and that it is pointing in the N-S direction (i.e., the earth’s magnetic field). The needle is parallel to the wire in this position, as indicated in figure (a).

(a) When a key is opened, the needle does not deviate and points in the direction of the N-S axis.

(2) When the key is pressed, a current runs through the wire in the direction of A to B (i.e., from south to north), and the needle’s north pole (N) deflects towards the west, as shown in figure (b).

(b) When the key is pressed, the needle’s north pole (N) deflects to the west.
(3) When the direction of current in the wire is reversed by reversing the connections at the battery terminals as indicated in figure, the needle’s north pole (N) deflects towards the east (c).

(c) When the current in the wire is reversed, the needle’s north pole (N) deflects towards the east.

(d) When the current in the wire is flowing from A to B, the north pole (N) deflects towards the east if the compass needle is situated directly above the wire.
(4) If the compass needle is placed immediately above the wire and the current direction in the wire is from A to B, the north pole (N) deflects towards the east. If the current in the wire is flowing from B to A, however, the needle deflects to the west, as illustrated in figure (e).

(a) If the compass needle is placed directly above the wire and the current in the wire is flowing from B to A, the needle deflects to the west.
According to these findings, a current-carrying wire generates a magnetic field around it.