Application of a Potentiometer—

1. Measurement of emf of a cell
2. Comparison of emfs of two primary cell
3. Measurement of Internal Resistance if a cell

Measurement of emf of a cell—

Let we have a cell of unknown emf (V). The positive terminal of this cell is connected to that end of the wire of potentiometer which is connected with the positive terminal of potentiometer battery (E). Now, we connect the negative terminal to a galvanometer and the second wire slide on the potentiometer wire of length (L). On sliding the wire we get a length ‘l’ at which we get null point.

Since, the total emf of battery is distributed over the entire length of the wire,

Comparison of emfs of two primary cell-

Let we have two cells of unknown emfs  E₁ and E₂ respectively. We connect both cells one by one with the potentiometer as per described above to measure the emf of the cell and we get lengths l₁ and l₂ respectively .

Measurement of Internal Resistance if a cell

To measure the value of internal resistance first we connect the cell as described above. Let l₁ be the balancing length of the wire, then emf of the cell