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

Question

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

Infinity Learn · Accepted Answer

Length $$L=100$$ cm       Resistance $$R=10$$ Ω     Series resistance $$RS=40$$ Ω     Battery of  emf $$E=2$$ V     Balancing length $$l=40$$ cm     emf of the cell in secondary circuit,$$E1=(i$$ρ$$)l$$     $$E1=(ER+RS)$$ RLl          $$=(210+40)$$ $$10100$$×$$40$$         $$=2$$×$$10$$×$$4050$$×$$100$$         $$=850$$     ∴  $$E1=0.16$$ V

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