Which characteristic must a transformer have to step up its input voltage?

To step up its input voltage, a transformer must have more turns of wire on its secondary winding than on its primary winding. This relationship is defined by the transformer turns ratio, which states that the ratio of the output voltage to the input voltage is directly proportional to the ratio of the number of turns in the secondary winding to the number of turns in the primary winding.

When the secondary winding has more turns, it creates a higher output voltage compared to the input voltage. This principle is fundamental in transformer operation, allowing us to increase voltage levels effectively for various applications, such as in power transmission where high voltages are needed to reduce energy loss over long distances.

In contrast, scenarios like having fewer turns on the secondary, equal turns on both windings, or changing the core material do not achieve the step-up effect. Fewer turns on the secondary would result in a step-down transformer, equal turns would maintain the input voltage, and while core material affects efficiency and losses, it does not determine the step-up or step-down functionality. Thus, having more turns on the secondary is the correct characteristic for stepping up voltage.