The voltage across the primary winding is 350,000 V, and the voltage across the secondary winding is 17,500 V. If the secondary winding has 600 coils, how many coils are in the primary winding?

For an ideal transformer, the voltage ratio equals the coil-turns ratio: primary coils ÷ secondary coils = primary voltage ÷ secondary voltage. Here, 350,000 ÷ 17,500 = 20, so the primary has 20 times as many coils as the secondary. Multiply 600 by 20 to get 12,000 coils, choice C.

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