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:

Options

A. `7 Omega`
B. `9 Omega`
C. `11 Omega`
D. Zero

Answer

C

Explanation

Given, emf of cell E= 200V
Internal resistance of cells `= Omega`
D. C. main supply voltage V = 220 V
External resistance R = ?
`r = (( E - V)/ (V))R" "1= ((20)/( 220)) xx R`
`therefore R = 11 Omega`.