To determine the internal resistance of a primary cell using a potentiometer

Aim

To determine the internal resistance of a primary cell using a potentiometer.

Apparatus

A potentiometer, a battery, two one-way keys, a rheostat of law resistance, a galvanometer, a high resistance box, a fractional resistance box (1-10Ω), an ammeter, a voltmeter (0-5V), a cell, a jockey, a set square, connecting wires & piece of sand paper.

Observations:

1. EMF of battery = 2V

EMF of cell = 1.35V

Result:

Precautions:

1. The EMF of the battery should be greater than that of cell.
2. For one set of observations, the ammeter reading should remain constant.
3. Rheostat should be adjusted so that initial will point lies on last wire of potentiometer.

Sources of Error:

1. The auxiliary battery may not be fully charged.
2. End resistance may not be zero.
3. Heating of potentiometer wire by current, may introduce some error.