USING POTENTIOMETER AIM To compare the emf of the given two cells using a potentiometer. APPARATUS REQUIRED Battery eliminator, key, rheostat, DPDT switch, Lechlanche and Daniel cells, galvanometer, high resistance box, pencil jockey and connecting wires. FORMULA ε ε = l l (no unit) where, ε and ε are the emf of Lechlanche and Daniel cells respectively (V) l and l are the balancing lengths for Lechlanche and Daniel cells respectively (cm) CIRCUIT DIAGRAM ( ) J K Bt D M N N M M Rh G HR ε ε PROCEDURE • The apparatus is arranged as shown in the circuit diagram. • The primary circuit consisting of battery, key and rheostat is connected to the potentiometer in series.
• The positive poles of the cells are connected to terminals M & M and the negative poles to terminals N & N of the DPDT switch. The potentiometer is connected to the common terminals M and N as shown in the circuit. • Using the two-way key, Lechlanche cell is included in the circuit. By sliding the jockey on the potentiometer wire, the balancing point is found and the corresponding balancing length is measured.
• Similarly, the balancing length is found by including Daniel cell in the circuit. • The experiment is repeated for different sets of balancing lengths by adjusting the rheostat. • From different values of l and l , the ratio of emf of the two cells is calculated. XII- - ) XII- - ) - - - - PRACTICAL OBSERVATION Table: To find the ratio of emf of two cells S.No Balancing length for Lechlanche cell, l (cm) Balancing length for Daniel cell, l (cm) ε ε = l l Mean ε ε CALCULATION ε ε = l l RESULT Ratio of emf of the given two cells = (no unit) Note: DPDT switch Double Pole Double Throw (DPDT) switch is a -terminal key with a throw switch (metal handle) attached to the common terminals M and N.
The two-given cells are connected to the pairs of terminals M & M and N & N . When the handle is thrown to one side, say M & M , the cell that is connected to that pair of terminals is included with the primary circuit. XII- - ) XII- - ) - - - - PRACTICAL