State the principle of potentiometer. Draw a circuit diagram used to compare the e.m.f. of two primary cells. Write the formula used. How can the sensitivity of a potentiometer be increased?

The potentiometer works on the principle that when a constant current flows through a wire of uniform cross sectional area, potential difference between its two points is directly proportional to the length of the wire between the two points. 

formula used : E₁/E₂ = l₁/l₂
where E₁ : E.M.F. of cell 1.
           E₂ : E.M.F. of cell 2.
           l₁: balancing length of cell 1.
           l₂: balancing length of cell 2.

A potentiometer is said to be sensitive if it can measure very small potential differences. It's sensitivity can be increased by increasing the no. of wires of the potentiometer.

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