A d.c. main supply of e.m.f. 220   V is connected across a storage battery of e.m.f. 200   V…

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  Ω . The battery terminals are connected to external resistance R. The minimum value of R, so that a current passes through the battery to charge it is:
  1. 9 Ω
  2. 7 Ω
  3. 11 Ω
  4. 0

Solution

Given, 
emf of cell E = 200 V 
Resistance =  1Ω 
D. C. main supply voltage V = 220V
External resistance R = ?

r=E-VVR
1=20220×R
∴  R=11Ω
 

Asked in: JEE Main 2014 (09 Apr Online)

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