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A transformer having efficiency of 90% is working on 200V and 3kW power supply. If the current in the secondary coil is 6A, the voltage across the secondary coil and the current in the primary coil respectively are:

1. 300V, 15A
2. 450V, 15A
3. 450V, 13.5A
4. 600V, 15A

Correct answer: 450V, 13.5A

Solution

The power output of the transformer is 90% of the input power, i.e., 0.9 × 3000 W = 2700 W. Using P = VI, the secondary voltage is V = P/I = 2700/6 = 450 V. The primary current is I = P/V = 3000/200 = 15 A.

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