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A step-up transformer operates on a 230 V line and supplies a load of 2 ampere. The ratio of the primary and secondary windings is 1 : 25. The current in the primary is

1. 25 A
2. 50 A
3. 15 A
4. 12.5 A

Correct answer: 25 A

Solution

In a transformer, power is conserved (ignoring losses). The power in the primary coil is equal to the power in the secondary coil. Using P = VI, we have VpIp = VsIs. Given Vp = 230 V, Is = 2 A, and the turns ratio is 1:25, Vs = 230 × 25 = 5750 V. Substituting, Ip = (Vs × Is) / Vp = (5750 × 2) / 230 = 25 A.

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