Now if the distance between points A and B is L, then we can write emf of standard cell E = Lv volt. That means, emf of the standard cell is just balanced by the voltage appearing in the resistor across points A and B. By adjusting this sliding end, a point like B is found where there is no current through the galvanometer, hence no deflection in the galvanometer. The other end of the galvanometer is in contact with the resistor via a sliding contact as shown in the figure above. Now, the positive terminal of a standard cell is connected to point A on the resistor and the negative terminal of the same is connected with a galvanometer. Suppose, by adjusting the rheostat we get v volt voltage drop appearing per unit length of the resistor. Hence, the voltage drop per unit length of the resistor is equal throughout its length. The resistor has the uniform electrical resistance per unit length throughout its length. Now let’s think about another circuit, where a battery is connected across a resistor via a switch and a rheostat as shown in the figure below.
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