| A d.c. main supply of e.m.f. 220 V is connected across a storage battery of e.m.f. 200 V through a resistance of \[1\Omega .\] |
| The battery terminals are connected to an external resistance R. The minimum value of R, so that a current passes through the battery to charge it is: [JEE ONLINE 09-04-2014] |
A) \[7\Omega \]
B) \[9\Omega \]
C) \[11\Omega \]
D) Zero
Correct Answer: C
Solution :
| [c] Given, emf of cell E = 200 V |
| Internal resistance of cells \[=1\Omega \] |
| D. C. main supply voltage V = 220 V |
| External resistance R = ?\[r=\left( \frac{E-V}{V} \right)R\] |
| \[1=\left( \frac{20}{220} \right)\times R\]\[\therefore \]\[R=11\Omega .\] |
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