Q.

Resistance of a potentiometer wire of length 4 m is 10 Ω and emf of its driving cell is 4 volt. What resistance must be added in series with potentiometer wire so that 3 m length of potentiometer wire can balance a cell of emf 2 volt ?

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a

10 Ω

b

15 Ω

c

1.5 Ω

d

5 Ω

answer is D.

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Detailed Solution

Resistance per unit length of potentiometer wire is λ=104 Ω/m=2.5 Ω/mAfter resistance R is inserted, in potentiometer wire circuit, current i=410+R A∴3 x 2.5 x 410+R=2⇒R=5 Ω
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