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Question

AB is a potentiometer wire of length 100 cm and its resistance is 10 Ω. It is connected in series with a battery of emf 2 V and resistance 40 Ω. If a source of unknown emf E is balanced by 40 cm length of the potentiometer wire, the value of E is

A
0.8 V
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B
1.6 V
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C
0.08 V
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D
0.16 V
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Solution

The correct option is D 0.16 V
Potential gradient across potentiometer wire is

dVdl=E0RAB(RAB+R)L
=2×10(10+40)1
=0.4 Vm1

Unknown emf is
E=dVdx×l (l=40 cm)
E=0.4×40×102=0.16 V

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