Question:

Homework on transformers?

I hate feeling the need to justify myself, but I've seen a lot of answers telling askers to do their own homework. I'm trying to do so, but can't find any equations in the book relating power to voltage as well as turn number. Is it PviN? I've just seen Pvi, but that wouldn't apply to multiple loops. This is for ideal transformers by the way, so power for the secondary and primary coils is the same right? But are their vi's equal, or their viN's?The primary coil of a transformer has 200 turns and the secondary coil has 800 turns. The power supplied to the primary coil is 400 watts. What is the power generated in the secondary coil if it is terminated by a 20-ohm resistor?

Answer:

The turns ratio is 4:1 of the primary. The power supplied to the primary is 400W. So regardless of anything else, in a ideal transformer, 400W is available on the secondary. But voltage will be 4x higher, current 4x smaller, than the voltage and current in the primary. Disregarding all that, if there is 400W of power flowing in the primary, then 400W will be being dissipated in the 20 ohm resistor. Watts in watts out, but secondary load (resistance) controls the wattage. There is no way to tell the output voltage and current, without knowing the input voltage and current. But whatever they are, the product of voltage x current will be 400W, in this instance.

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