1.

Two cells of emf's approximately 5V and 10V are to be accurately compared using a potentiometer of length 400 cm.

Answer»

The battery that runs the potentiometer should have VOLTAGE of 8V.
The battery of potentiometer can have a voltage of 15V and R adjusted so that the potential drop across the wire slightly exceeds 10V.
The first portion of 50 cm of wire itself should have a potential drop of 10 V.
Potentiometer is usually USED for comparing resistances and not voltages.

SOLUTION :The battery of potentiometer can have a voltage of 15V and R adjusted so that the potential drop across the wire slightly exceeds 10V.
Potential difference between two voltage drop across two end of wire of potentiometer should be more than emf of cell whose emf value is tobe measured.
Here, emf of cell given si 5V and 10 V. hence , emf of MAIN cell should be more than 5 V and 10 V means should be 15 V. Hence. 4 V drop will be VARIABLE resistance .


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