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A uniform potentiometer wire AB of length 100 cm has a resistance of `5Omega` and it is connected in series with an external resistance R and a cell of emf 6 V and negligible internal resistance. If a source of potential drop 2 V is balanced against a length of 60 cm of the potentiometer wire, the value of resistance R isA. `1Omega`B. `2Omega`C. `4Omega`D. `6Omega`

Answer» Correct Answer - C
Current through the potentiometer wire is
`l=(6)/(R+5)`
`thereforeV=(6xx3)/((R+5))`
`2=(18)/(R+5)`
`R+5=9`
`R=4Omega`.


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