A 200-turn coil changes flux per turn from +3.0 × 10⁻⁴ Wb to −3.0 × 10⁻⁴ Wb in 0.020 s. (a) Find mean induced e.m.f. (b) Explain polarity and two output improvements. (c) An ideal transformer raises 120 V to 6000 V while transmitting 24 kW. Find both currents. (d) For cable resistance 8.0 Ω, compare high-voltage loss with direct 120 V transmission. (e) Explain the grid advantage.

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Mean e.m.f. 6.0 V; currents 200 A and 4.0 A; cable losses 128 W and 3.20 × 10⁵ W respectively. Flux change magnitude per turn is 6.0 × 10⁻⁴ Wb. Faraday's law gives mean e.m.f. NΔΦ/Δt = 200 × 6.0 × 10⁻⁴/0.020 = 6.0 V. Lenz's law makes induced effects oppose the flux change, conserving energy. More turns, larger area, stronger field or faster rotation increases rate of flux-linkage change. Ideal power conservation gives primary current 24000/120 = 200 A and secondary current 24000/6000 = 4.0 A. High-voltage cable loss I²R = 4.0² × 8.0 = 128 W. At 120 V, current 200 A gives 200² × 8.0 = 3.20 × 10⁵ W. High voltage reduces current for specified power, so heating falls with current squared. The voltage is stepped down near consumers for insulation practicality and safety.

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