Page 120 - Physics - XII

Investigatory Projects
Investigatory Projects

PROJECT - 1

Aim
To study various factors on which the internal resistance/E.M.F. of a cell depends.

Apparatus and Materials Required
A voltaic cell, a voltmeter, a resistance box, two one-way keys, connecting wires, a potentiometer, a rheostat

of low resistance, a galvanometer, an ammeter, a battery, a high resistance box, a jockey, and sand paper.
R K
RB 2
E 1 RB
– + + – 2 Scale for measuring
E K G distance between plates
A 1 3 P
B
J Scale for measuring
K 1 depth up to which
plates are dipped
Rheostat Cu plate Zn plate
(Rh)
A 1 M H SO (sol.)
Fig. 1.1: Circuit diagram for measuring internal 2 4
resistance of cell using potentiometer Fig. 1.2: Voltaic cell

Principle/Theory

Internal resistance of a cell: The resistance off ered by the electrolyte to the passage of current through the
interior of the cell is called the internal resistance of the cell. It is denoted by the symbol ‘r’.

Electromotive force (e.m.f.) of a cell (E): The potential diff erence across the two terminals of the cell in
an open circuit (when no current is drawn from the cell) is called e.m.f. of a cell. It is denoted by E.
Factors on which the internal resistance of a cell depends: Internal resistance of a cell depends upon

the following factors:
(i) Distance between the electrodes: Internal resistance (r) of a cell is directly proportional to the
distance (d) between the two electrodes of the cell, i.e. the length of the electrolyte through which the
current fl ows, i.e.
r ∝ d
(ii) Common area of the electrodes: Internal resistance (r) of a cell is inversely proportional to the
common area (A) of the two electrodes dipping in the electrolyte, i.e.

1
r ∝
A

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