Q1 of 5 Page 127

A potentiometer wire of length 1m has a resistance of 10 ohms. It is connected to a 6V battery in series with a resistance of 5 ohms. Determine the EMF of a primary cell 'e' which gives a balance point of 40 cm.

To find: the EMF of a primary cell 'e' which gives a balance point of 40 cm.


Resistance of potentiometer = R = 10 ohms


External battery has voltage = V = 6 V


Resistance in series = r = 5 ohms


Length of the potentiometer wire = L = 100


Equivalent resistance = R + r


Total current flowing through circuit = I


Using Ohm's law,







Let voltage potentiometer


Again using Ohm's law,





We know,



l = length across which e gives a balance point


Where k is the potential gradient



So,









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