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A potentiometer wire of lengthh 100 cm h...

A potentiometer wire of lengthh 100 cm has resistance `5Omega`. It is connected in series with a resistance and a cell of emf 2 v and of negligible internal resistance. A source of emf 5 mv balanced by 10 cm length of potentiometer wire. The value of external resistance is___

A

`540Omega`

B

`195Omega`

C

`190Omega`

D

`990Omega`

Text Solution

Verified by Experts

The correct Answer is:
B
`E^(')=irhol=[(E)/(R+R_(3))](R)/(L).l`
`5xx10^(-3)=[(2)/(5+R_(3))](5)/(100)xx10`
`R_(S)=195Omega`
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