To compare the EMF's of given two primary cells using a potentiometer

 COMPARISON OF EMFs OF TWO CELLS

In this experiment, we compare the EMF of two given primary cells, namely, Leclanche cells and Daniel cells using a Potentiometer. The primary cell is a battery designed to be used once and discarded, which has high density and gets discharged slowly. 

Aim of the experiment :

To compare the EMFs of given two cells using a potentiometer.

Apparatus required :

1. Potentiometer
2. Battery
3. Primary cells namely Leclanche & Daniel cells
4. Two-way key
5. Rheostat
6. Plug Key
7. Connecting wires
8. Galvanometer

Principle of the experiment :

Principle of the potentiometer: When a steady current flows through a conducting wire of uniform thickness, the potential difference between any two points on it is directly proportional to the length of the wire between those two points.

E is directly proportional to the length  OR  E1/E2 = l1/l2

Formula :

01. The ratio of EMFs of the cells is given by = E1/E2 = l1/l2

Where,

            E1 - EMF of the first cell

            E2 - EMF of the second cell

            l1 - Balancing length for the first cell

            l2 - Balancing length for the second cell

Circuit diagram :

To compare the EMFs of given two primary cells using a potentiometer 

Procedure :

• The connections are made as shown in the circuit diagram respectively.

• The key K is closed and the two-way key is connected to cell E1. The circuit is checked for opposite deflections by placing Jockey at the two ends of the wire PQ alternatively.

• The Jockey is moved on the potentiometer wire from P towards the end Q till the galvanometer shows zero deflection. The balancing length l1 is measured two-way

• The two-way key is disconnected from cell E1 and connected to cell E2. The balancing lengtmeasuredmessured. The ratio of E1/E2 is calculated using the formula E1/E2 = l1/l2

• The experiment is repeated by shifting the contact point of the rheostat and the average value of the ratio of EMFs of the cell is found.

Observation :

Note down the observed values in the respective tabular column.

Trial No	Balencing length, l1 in (cm)	Balencing length, l2 in (cm)	E1/E2 = l1/l2
01.
02.
03.
04.
05.
			Average value of E1/E2 = ...........

Calculations :

E1/E2 = l1/l2 ( Show the substitution and calculation for each trail )
Average value of  E1/E2 = ................................ = ......................................

Result :

The ratio of EMFs of the cells E1/E2 = ................................

Note :

01. Key plugged into the resistance box must ensure good electrical contact.

02. Position of rheostat contact should not be disturbed before finishing the task of finding the balance length with both cells.