What does the turns ratio of a transformer determine?

• A. Frequency
• B. Power
• C. The voltage change between primary and secondary
• D. The color of insulation

Answer: (C)

The turns ratio tells you how the voltage on the secondary relates to the voltage on the primary. In an ideal transformer, the secondary voltage is the primary voltage multiplied by the ratio of the number of turns on the secondary to the number on the primary (Vs = Vp × Ns/Np). So more turns on the secondary means a higher output voltage (step-up), while fewer turns mean a lower output voltage (step-down). The frequency comes from the power source and stays essentially the same through the transformer. Power is conserved in an ideal case, so when voltage goes up and current goes down (and vice versa) to keep the input and output powers balanced, within the limits of losses. The color of insulation has no bearing on the voltage transformation.