Final answer:
When current flows through a wire oriented north-south, a compass placed above will deflect according to the magnetic field produced by the current, with the direction determined using the right-hand rule.
Step-by-step explanation:
If a horizontal wire is oriented along a north-south line and carries a current, and a compass is placed above it, the compass needle will deflect due to the magnetic field created by the current flowing through the wire. When a current flows through a wire, it generates circular loops of magnetic field around the wire. Using the right-hand rule, if the current flows south, you point your thumb southward (in the direction of the current) and your fingers will curl around the wire, indicating the direction of the magnetic field loops. In this situation, the right side of the wire (east) will have the magnetic field pointing into the page (marked with an X), while the left side (west) will have the magnetic field coming out of the page (marked with a dot).
The compass needle aligns itself tangentially to these magnetic field loops. If the current is sufficiently strong, the compass needle will likely show a noticeable deflection from Earth's magnetic field towards the wire's magnetic field. The stronger the current, the more significant the deflection of the compass needle will be.