A transformer has 140 turns in the primary and 280 turns in the secondary. If the primary current is 4 A, the secondary current (assuming an ideal transformer) is:

4 A
2 A
6 A
10 A

Correct answer: 2 A

Solution

Ideal transformer: Ip Np = Is Ns, so Is = Ip Np/Ns = 4 * 140/280 = 2 A. This is a step-up transformer (more secondary turns), so current decreases.

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