Potentiometer is used to

State the working principle of potentiometer. With the help of the circuit diagram, explain how a potentiometer is used to compare the emf's of two primay cells. Obtain the required expression used for comparing the emfs. Write two possible causes for one sided deflection in a potentiometer experiment.

A standard cell of emf e_(0)=1.11 V is balanced against 72 cm length of a pootentiometer. The same potentiometer is used to measure the potential difference across the stndard resistance R=120 Omega . When the ammeter shows a current of 7.8 mA, a balanced lengh of 60 xm is obtained on the potentiometer. (i) Determine the current following through the resistor. (ii) Estimate the error in measurement of the ammeter.

Assertion : Potentiometer is used only to compare potential differences. Reason: The potentiometer draws current from the voltage source being measured .

A potentiometer is used for the compaisem of e.m.f. of two cells E_(1) and E_(2) . For cell E_(1) the no deflection point os obtained at 20 cm and for E_(2) the no deflection point is obtained at 30 cm . The ratio of their e.m.f.'s will be