Answer
The fields produced by the 2 wires tend to cancel each other.
Work Step by Step
A single current-carrying wire creates a magnetic field that encircles the wire, as in Figure 28.9. If the direction of the current were to be reversed, the magnetic field would change direction everywhere.
Therefore, when 2 wires carrying currents in opposite directions are wrapped around one another, the fields they create nearly cancel each other out.
