Which of the following is an effect of mutual induction?

Mutual induction is a principle that occurs when a change in the current flowing through one coil induces a voltage in another nearby coil. This effect is fundamental in the operation of transformers, which are reliant on mutual induction to transfer electrical energy between circuits at different voltage levels. The transformation of power involves changing the voltage while conserving power, and this is achieved through the interaction of the magnetic fields generated by each coil.

In contrast, the other options do not relate directly to the principle of mutual induction. While heat loss in wires can occur due to resistive heating, it is not a result of mutual induction. Changing the frequency of an AC signal is influenced by other factors such as circuit capacitance and inductance but not by mutual induction itself. Regulating DC voltage levels typically involves components such as voltage regulators, rather than the inductive properties of coils. Thus, transforming power in a circuit through the mechanism of mutual induction is the correct focus here, highlighting its critical role in electrical systems.