Final answer:
A transformer with a single primary voltage rating should be connected to a source with that same voltage. The transformer equation relates the primary and secondary voltages to their respective coil turn ratios, relevant for step-up and step-down transformers.
Step-by-step explanation:
If a transformer only has one number for a primary voltage rating, it should be connected to an electrical source with the same voltage as the rating. This ensures that the transformer operates safely and efficiently.
The transformer's function is to either increase or decrease the voltage through electromagnetic induction. This process is captured by the transformer equation, which states that the ratio of the secondary voltage (Vs) to the primary voltage (Vp) in a transformer equals the ratio of the number of loops in the secondary coil (Ns) to the number of loops in the primary coil (Np): Vs/Vp = Ns/Np. For a step-up transformer, which increases voltage, the number of turns in the secondary coil is greater than in the primary. Conversely, for a step-down transformer, which decreases voltage, the primary coil has more turns than the secondary.