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I just started network theory and stuck to this problem, in book it is written that an ideal transformer supplies constant power, so I randomly assume a question as shown in figure and try to find current in secondary side but I got two different answers for same current calculation, so where I'm going wrong and how to calculate current in this case correctly?


1 Answer 1


The mistake you made was in pre-defining the primary current as 2 amps. You broke ohms law at this point (retrospectively).

If there is 6 amps flowing in the secondary due it producing 30 volts across a 5 ohm load then clearly, there is more current in the primary than what flows in the secondary hence, your figure of 2 amps is wrong.

$$I_1 = \dfrac{V_2\times I_2}{V_1} = \dfrac{30\times 6}{10} = 18$$

Primary current has to be 18 amps.


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