AB is a potentiometer wire of length 100cm and its resistance is 10Ω. It is connected in series with a battery of emf 2V and resistance 40Ω. If a source of unknown emf E is balanced by 40cm length of the potentiometer wire, the value of E is
A
0.8V
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B
1.6V
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C
0.08V
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D
0.16V
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Solution
The correct option is D0.16V Potential gradient across potentiometer wire is
dVdl=E0RAB(RAB+R)L =2×10(10+40)1 =0.4Vm−1
Unknown emf is E=dVdx×l(∵l=40cm) E=0.4×40×10−2=0.16V