Final answer:
In a step-up transformer, the primary winding has a higher current and lower voltage, while the secondary has a higher voltage and lower current. In a step-down transformer, it's the reverse, with the primary having a higher voltage and the secondary having a lower voltage and higher current.
Step-by-step explanation:
To distinguish the primary winding from the secondary winding in a step-up transformer, you need to look at the voltage and current characteristics. In a step-up transformer, the primary winding has a higher current and a lower voltage compared to the secondary winding. Conversely, the secondary winding in a step-up transformer will have a higher voltage but a lower current than the primary winding due to the transformer's function of increasing the voltage.
In the case of a step-down transformer, the primary winding will have a higher voltage and a lower current, while the secondary winding will have a lower voltage and a higher current. This distinction is because a step-down transformer decreases the voltage from the primary to secondary side.