Step 1: Understanding the Setup.
In the potentiometer, the unknown cell is connected in series with a known external resistance. A galvanometer is used to detect the potential difference, and a sliding contact (or jockey) is used to vary the length of the potentiometer wire.
Step 2: Procedure.
1. First, use the potentiometer to measure the potential difference across the cell when no current is drawn from it. This gives the emf of the cell.
2. Then, a small known resistance is connected in series with the cell. The sliding contact is adjusted until there is no current in the galvanometer, indicating the potential difference across the cell and the external resistance is equal.
3. Using Ohm's Law, calculate the internal resistance of the cell using the relation:
where is the emf of the cell, is the measured potential difference, and is the current through the external resistance.
Step 3: Conclusion.
By determining the emf and the voltage drop across the internal resistance, the internal resistance of the cell can be accurately calculated using the potentiometer.