Final answer:
The 54-watt transformer with an output voltage of 13V and an input current of 25A is a step-down transformer, as it reduces the voltage from a higher input voltage level to a lower output voltage level.
Step-by-step explanation:
When considering whether a transformer is a step-up or step-down transformer, one must look at the voltage levels. In the case of the 54-watt transformer with an output voltage of 13V and an input current of 25A, the determination is made based on comparing input and output voltages. Since transformers transfer power with a near 100% efficiency rate, the power input (represented by Ip times Vp) is essentially equal to the power output (represented by Is times Vs).
For a transformer operating at such efficiency, if the output voltage is lower than the input voltage, it is considered a step-down transformer because it decreases the voltage. The fact that this transformer has an output voltage of 13V suggests that it is a step-down transformer, as it is lowering the voltage from a hypothetical higher input voltage level (not specified in the question). As a result, we can conclude that this transformer is indeed stepping down the voltage, thereby classifying it as a step-down transformer.