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A battery is charged at a potential of 15V for 8 hours when the current flowing is 10A. The battery on discharge supplies a current of 5A for 15 hours. The mean terminal voltage during discharge is 14V. The “watt-hour” efficiency of the battery is

1. 87.5%
2. 82.5%
3. 80%
4. 90%

Correct answer: 87.5%

Solution

The energy supplied to the battery during charging is given by E_charge = V_charge × I_charge × t_charge = 15 × 10 × 8 = 1200 Wh. The energy delivered by the battery during discharge is E_discharge = V_discharge × I_discharge × t_discharge = 14 × 5 × 15 = 1050 Wh. The watt-hour efficiency is (E_discharge / E_charge) × 100 = (1050 / 1200) × 100 = 87.5%.

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