Final answer:
In a step-up transformer, the primary winding has fewer turns and is connected to a lower voltage, whereas the secondary winding has more turns and produces a higher voltage output, adhering to Faraday's law of induction.
Step-by-step explanation:
To distinguish the primary winding from the secondary winding in a step-up transformer, we need to look at the number of turns and the voltage levels across each winding. The primary winding, which is connected to the alternating voltage (Up(t)), usually has fewer turns (Np) than the secondary winding if it's a step-up transformer. Conversely, the secondary winding has more turns (Ns) and is connected to a load resistor (Rs). In a step-up transformer, the voltage increases from the primary to the secondary side, which can be observed by the voltage difference between the two windings. The transformer's operation relies on Faraday's law of induction, where a changing current in the primary coil induces a current in the secondary coil through a magnetic field confined by the ferromagnetic core.