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An ideal transformer (100% efficient) draws a primary power input of 10 kW. With the transformer on load, the secondary current is 25 A and the primary-to-secondary turns ratio is 8: 1. Find the potential difference applied across the primary coil.

1. (10⁴ * 8² / 25) V
2. (10⁴ * 8 / 25) V
3. (10⁴ / (25 * 8)) V
4. (10⁴ / (25 * 8²)) V

Correct answer: (10⁴ * 8 / 25) V

Solution

Power conserved: P = 10 kW = 10⁴ W appears on the secondary as Vₛ * Iₛ, so Vₛ = 10⁴ / 25 V. The turns ratio Np:Ns = 8:1 means Vₚ = 8 Vₛ = 8 * (10⁴/25) = (10⁴ * 8 / 25) V.

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