The 335 kV AC electricity from a power transmission line is fed into the primary coil of a transformer. The ratio of the number of turns in the secondary to the number in the primary is $\dfrac{\textrm{N}\textrm{s}}{\textrm{N}\textrm{p}} = 1000$ . (a) What voltage is induced in the secondary? (b) What is unreasonable about this result? (c) Which assumption or premise is responsible?

Video Transcript

This is College Physics Answers with Shaun Dychko. 335 kilovolts is input to a step-up transformer that has a ratio of secondary turns to primary turns of 1000 and our question is what is the voltage output in other words? So we have V s over V p is N s over N p so this is voltage output divided by voltage input equals number of turns in the output divided by the number of turns in the input and multiply both sides by V p and we get V s then is the input voltage multiplied by this ratio so that's 335 kilovolts times 1000 which is 335 megavolts and that is a very high voltage that would spark through the air over fairly large distances and so it would be unsafe to transmit it or use it in any device and so the input voltage must be too high. It's possible to have a step-up transformer with a ratio of turns of 1000 but this 335 kilovolt input is unrealistic.