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Home Physics Class 12 Physics To determine the internal resistance of a primary cell using a potentiometer
Class 12 Physics Lab Experiments

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.

Circuit Diagram

Observations:

  1. EMF of battery = 2V

EMF of cell = 1.35V

  • Table for lengths:
  • Position of Null pt(cm)
    Sr. No. Without shunt R,ι11 cm Without shunt R,ι21 cm Value of shunt resistance R(Ω) Internal resistance r = [ι122]RΩ
    1 571 67 1 7.53
    2 619 91 1.5 8.10
    3 689 129 2 8.68
    4 749 196 2.5 7.05
    5 882 221 3 8.97
    6 950 289 3.5 7.9

    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.