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LovePhys

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## Homework Statement

For a transformer, the ratio number of turns on the transformer secondary : number of turns on the transformer primary = 21 : 1200. If the input voltage is 120V AC, what is the output voltage?

## Homework Equations

[itex] \frac {N_{P}}{N_{S}}=\frac {V_{P}}{V_{S}} [/itex]

## The Attempt at a Solution

I used the equation above to calculate the output voltage:

[itex] \frac {1200}{21}=\frac {120}{x} [/itex]. So the output voltage, which is x, is 2.1V

However, the answer of the book is 4.2V. I wonder if I have to double the value of the output voltage to get the final answer (the peak-to-peak output voltage). But I think the transformers always work with AC current and the formula above has already been constructed with AC current. Can anyone please correct me if I am wrong?

I appreciate any help given! Thank you!