Which two terminals on the secondary will have 90 VAC across them if 300 VAC is applied to the primary of the transformer?

When analyzing a transformer, the relationship between the primary and secondary voltages is governed by the turns ratio. If a transformer has a primary voltage of 300 VAC, the secondary voltage will depend on its turns ratio.

In this scenario, a secondary voltage of 90 VAC is expected. This means that the transformer reduces the voltage from the primary 300 VAC down to 90 VAC on the secondary side. Given this reduction, it’s important to understand how the terminals are configured and the reference points used when measuring voltage across them.

In many transformer configurations, points on the secondary winding would be indicative of the different phases or taps. If points 1 and 4 are selected as having a voltage difference of 90 VAC across them, it implies that point 1 is effectively at a certain potential relative to the neutral point or ground, and point 4 is at a higher potential of 90 VAC.

Therefore, the correct reasoning is that with the proper turns ratio, applying 300 VAC to the primary leads to a scenario where the voltage difference between points 1 and 4 equates to the expected reduced voltage of 90 VAC. The specific connections of the transformer must support this, allowing for these two points to exhibit the desired voltage difference.