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 ............... $\Omega$
JEE MAIN 2014, Diffcult
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