A battery is charged at a potential of $15\, V$ for $8$ hours when the current flowing is $10\, A$. The battery on discharge supplies a current of $5\, A$ for $15$ hours. The mean terminal voltage during discharge is $14\, V$. The "Watt-hour" efficiency of the battery is .............. $\%$
AIPMT 2004, Medium
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Watt hour efficiency$ = \frac{{{\rm{Discharging}}\,\,{\rm{energy}}}}{{{\rm{Charging}}\,\,{\rm{energy}}}}$

$ = \frac{{14 \times 5 \times 15}}{{15 \times 8 \times 10}}$$ = 0.875$$ = 87.5\% $

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