Hydroelectric efficiency from power ratio Steps:

• Compute input power: P_in = mass flow rate × g × head = 10 kg/s × 9.8 m/s² × 280 m.
• Compute output power: P_out = potential difference × current = 980 V × 205 A.
• Divide output by input: P_out / P_in.
• Multiply by 100% to get efficiency percentage. Why D is correct:
• Matches the formula η = (P_out / P_in) × 100%, where hydroelectric efficiency reflects converted gravitational potential to electrical energy. Why the others are wrong:
• A. 8.3%: Assumes unrealistically high losses, violating energy conservation.
• B. 12%: Far below typical hydroelectric efficiencies of 80-95%.
• C. 83%: Slightly understates the precise power conversion ratio.

Final answer: D