The second conductor of an unbalanced circuit serves what purpose?

In an unbalanced circuit, the role of the second conductor is primarily to act as a shield that helps protect the signal wire from external electromagnetic interference. This shielding is critical in maintaining the integrity of the signal being transmitted along the wire, especially in environments where electromagnetic noise can disrupt the operation.

The shielding provided by the second conductor creates a barrier around the signal carrying wire. This allows the circuit to effectively resist interference from external sources while ensuring that the primary signal can travel without degradation. Unbalanced circuits often use a single conductor for the signal and another for grounding or shielding, which is essential in many audio and video applications.

The other options do not accurately represent the function of the second conductor in an unbalanced circuit. It does not serve as a power source, nor does it inherently increase the circuit's resistance or separate signals into multiple channels. Instead, its primary function is to assist in creating a more robust and interference-resistant signal transmission path through shielding.