Question

Describe the construction and working of a potentiometer. Explain, drawing circuit diagram, how emfs of two cells can be compared with its help?

Answer 1

The potentiometer is a device used to compare the e.m.f of two cells. It works on the principle that when a constant current flows through a wire of uniform cross-sectional area, a potential difference between its two points, is directly proportional to the length of the wire between the two points.

Construction: It consists of a long uniform cross-sectional area and of $10m$ in length. The material of the wire should have a high resistivity and low-temperature coefficient. The wires are joined in series by using thick copper strips. A matter scale is also attached to the wooden board.

Comparing E.m.f of two cells:

Using a potentiometer, we can determine the e.m.f of a cell by obtaining the balancing length $l$ of the potentiometer wire is equal to the e.m.f of the cell, as no current is being drawn from the cell, Then,

$E\alpha l$

or $E=kl$ {$k:Potentialgradient$}

For comparing e.m.f of two cells,

$\frac{E_1}{E_2}=\frac{k{l}_1}{k{l}_2}=\frac{l_1}{l_2}$