Q148 / 160 · AP EAMCET 2022 (05 Jul Shift 2) · Physics

A battery with a $12 \mathrm{~V}$ emf has an initial charge of $80 \mathrm{~A} . h$. If the potential across the terminals stays constant until battery is completely discharged, then this battery can deliver energy at the rate of $120 \mathrm{~W}$ for a time

  • A
    $16 \mathrm{~h}$
  • Correct answer
    B
    $8 \mathrm{~h}$
  • C
    $4 \mathrm{~h}$
  • D
    $5 \mathrm{~h}$

Solution

We have, $\begin{aligned} \Delta \mathrm{U} & =\mathrm{P} \Delta \mathrm{t}=\mathrm{q} \varepsilon \\ \Delta \mathrm{t} & =\frac{\mathrm{q} \varepsilon}{\mathrm{P}}=\frac{(80 \mathrm{~A} . \mathrm{h}) \times(12 \mathrm{~V})}{120 \mathrm{~W}}=8 \mathrm{~h}\end{aligned}$

Hence, the correct answer is option: 'B'.

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