Final answer:
The compass needle beneath a copper wire will deflect in the opposite direction when the current through the wire reverses. This happens due to the reversal of the magnetic field around the wire, which is dictated by the right-hand rule for magnetic field direction with respect to current flow.
Step-by-step explanation:
When the direction of current reverses in a copper wire, the compass needle underneath the wire will deflect in the opposite direction. This is due to the change in the direction of the magnetic field produced by the wire. According to the right-hand rule (RHR-2), with a current flowing from south to north, the magnetic field circles the wire in such a way that it would emerge from the page on the east side of the wire and enter the page on the west side. If the current is reversed, the magnetic field reverses too, causing the compass needle to align with the new direction of the field.
Since a compass needle points along magnetic field lines, it initially aligns with Earth's magnetic field. When a current passes through a wire, the needle deflects because of the interaction between the magnetic field of the Earth and the magnetic field created by the moving charges in the wire. If the current flows in the opposite direction, the induced circular magnetic field around the wire also reverses, and as a result, the compass needle will also deflect in the opposite direction.