What characteristic defines a step-up transformer in terms of wire turns?

A step-up transformer is characterized by having more turns of wire on the secondary side compared to the primary side. This design allows the transformer to increase the voltage of an alternating current (AC) signal while reducing the current proportionally, based on the principle of conservation of energy.

The relationship between the number of turns and the voltage in a transformer is defined by the transformer equation, which states that the ratio of the voltages across the primary and secondary sides is equal to the ratio of the number of turns on those sides. Therefore, if the secondary side has more turns than the primary side, the voltage output will be greater than the voltage input, fulfilling the function of a step-up transformer.

The other choices refer to different configurations that do not achieve the step-up function. More turns on the primary side would denote a step-down transformer, as it would reduce the voltage. An equal number of turns would mean there is no change in voltage. Lastly, fewer turns leading to higher voltage contradicts the foundational principles of transformer operation, as it implies a decrease in turns results in an increase in voltage, which is not accurate. Understanding this concept is critical for anyone working with transformers in electrical engineering and related fields.