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A potentiometer of 100 cm has a resistan...

A potentiometer of 100 cm has a resistance of 10 `Omega`, connected to cell of emf 2 v and a resistance R. An emf of 10 m V is balanced against a length of 40 cm of the potentiometer wire. The value of R is

A

`580Omega`

B

`790Omega`

C

`270Omega`

D

`10Omega`

Text Solution

Verified by Experts

The correct Answer is:
B
`I=V/(r+R)=2/(10+R)`
40 cm wire has `4Omega`.
`therefore` P.D. area 40 cm = `V=Ixx4`
`10mV=2/(10+R)xx4`
`10xx10^(-3)=2/(10+R)xx4`
`R=790Omega`
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