TO COMPARE THE EMF OF TWO PRIMARY CELLS BY THE POTENTIOMETER:

# TO COMPARE THE EMF OF TWO PRIMARY CELLS BY THE POTENTIOMETER:

* Circuit diagram:

PRINCIPLE AND DERIVATION OF FORMULA:
In above circuit diagram shows the principle of potentiometer by which we can compare the EMF of two cells. For this we first complete the primary circuit and then two experimental cells are joined in the secondary circuit as their positive terminal are joined at one end of potentiometer wire on which the positive terminal of an accumulator cell is already joined and their negative terminal are joined with two way switched (k2) along with galvanometer (G) and Jockey (J).

when current is flowing in the Potentiometer wire by an accumulator cell and first primary cell is in the circuit by the help of two way switch (k2).
For this the balancing length L1 cm is obtained.

Let the potential gradient of potentiometer wire be “K” volt/cm

By the principle of potentiometer
EMF of first cell, E1 = k.L1 ------(1)

By the help of key (k2) first cell E1 is removed from the circuit and second cell E2 is coming in the circuit.
For this the balancing length L2 cm is obtained on potentiometer wire.

Again, By the principle of potentiometer
EMF of second cell, E2 = k.L2 --------(2)

Dividing eqn(1) by eqn(2)

E1/E2  =  k.L1 / kL2

[ E1/E2  =  L1/L2 ]

This is required formula

* OBSERVATION:

* PRECAUTION:

1) All connecting screws and plugs should be tied .

2) Positive terminal of each cell should be connected at one end of the Potentiometer wire .

3) EMF of an accumulator cell in primary circuit is more than that of experimental cell otherwise the position of null deflection does not obtained on whole length of potentiometer wire.