What is an identifying feature of a step-up transformer?

A step-up transformer is characterized by having more turns on the secondary winding compared to the primary winding. This design allows it to increase the voltage from the primary to the secondary side while reducing the current correspondingly, in accordance with the principle of conservation of energy.

In the operation of a step-up transformer, the input voltage is applied to the primary winding, which creates a magnetic field. This magnetic field induces a higher voltage in the secondary winding due to the higher number of turns. The resultant effect is an increased output voltage compared to the input voltage, making it ideal for applications where higher voltages are required, such as in power transmission over long distances.

The other choices do not accurately represent the function of a step-up transformer. For instance, having more turns on the primary winding or a lower voltage output would not fulfill the purpose of stepping up the voltage. Similarly, an absence of changes in turns would contradict the very definition of a step-up transformer, which is based on the ratio of turns between the primary and secondary windings. Thus, the feature of having more turns on the secondary winding is what distinctly identifies a step-up transformer.