This simulation shows the magnetic field for a pair of wires. Drag the blue points to adjust the direction and current magnitude of each of two wires. Click a point to toggle between movement in the xy-plane, and along the z-axis. The red vectors represent the current in each wire. Larger magnitudes correspond to larger currents.

[list=1][*]Make the current in one of the wires very small so that it can be neglected. What does the magnetic field of a lone wire look like?[/*][*]Make the currents of the two wires (close to) the same. How does the magnetic field of two parallel wires compare to the field of two anti-parallel wires?[/*][*]Just by looking at the field, can you tell whether two anti-parallel wires would attract or repel?[/*][/list]