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A potentiometer wire has length 4 m and ...

A potentiometer wire has length 4 m and resistance 8`Omega`. The resistance that must be connected in series with the wire and an accumulator of e.m.f. 2V, so as to get a potential gradient 1 mV per cm on the wire is :

A

79 ohm

B

81ohm

C

90ohm

D

100ohm

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