What do the primary leads of a transformer connect to?

The primary leads of a transformer connect to an AC power source because transformers are designed to operate with alternating current (AC). When AC is applied to the primary winding, it creates a varying magnetic field that induces a voltage in the secondary winding based on the principles of electromagnetic induction. This process allows the transformer to either step up or step down voltage levels effectively.

In contrast, connecting a transformer to a DC power source would not produce the required changing magnetic field, rendering it ineffective. Similarly, a battery provides direct current, which does not facilitate the functioning of a transformer in the same way as AC does. Grounding is unrelated to the primary leads as it pertains to safety and circuit stabilization rather than the operational aspect of the transformer. Therefore, the connection to an AC power source is essential for the proper functioning of a transformer.