in the construction of potentiometer in some books unkwown resistance is used instead of standard why is it so

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Solution

Construction of potentiometer uses nichrome wires or constantin wires which have standard fixed specific resistances but no standard resistance is required for construction of potentiometer. It is only the balance point that matters.

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A potentiometer has a wire of 100 cm length and its resistance is 10 ohms. It is connected in series with a resistance of 40 ohms and a battery of emf 2 V and negligible internal resistance. If a source of unknown emf E connected in the secondary is balanced by 40 cm length of potentiometer wire, the value of E is: