The potentiometer- Comparison of emf

# Materials Required

• Potentiometer
• Daniel cell
• Leclanche cell
• Jockey
• Battery eliminator
• Resistance box
• Galvanometer
• One way key
• Two way key
• Rheostat
• Ammeter
• Connecting wires

# Real Lab Procedure

• Arrange the required materials on a table and make the connections as per the connection diagram.
• Tight the plugs of the resistance box.
• Note the reading on the ammeter.
• To test the connection, insert plug in the one way key k1 and also in between the terminals a and c of the two way key. Introduce a sufficiently high resistance on the resistance box (R.B). Place the jockey at the two end points of the wire. Press the jockey at both end of the potentiometer wire and note the deflection in galvanometer. If the galvanometer shows opposite deflection, the connections are correct.
• Now, gently slide the jockey along the potentiometer wire and stop when null point is obtained.
• Measure the length l1 between this point and the end P of the potentiometer. It is the balancing length for the cell E1.
• Disconnect the cell E1 by removing the plug from the gap ac of the two way key and connect the cell E2 by inserting plug into the gap bc of the two way key.
• Again slide the jockey along the potentiometer wire to obtain the null point. Measure the new balancing length l2 for the cell E2 based on this point.
• Make sure that the reading on the ammeter is constant throughout the observation.
• Repeat the experiment by increasing the current by adjusting the rheostat and record the observations.
• Each time, the ratio between the emf’s of the given cells can be calculated using the relation,

$\dpi{100} \frac{E_1}{E_2}=\frac{l_1}{l_2}$

# Simulator Procedure (As performed through Online Labs)

• Select the first primary cell form the drop down list.
• Select the second primary cell form the drop down list.
• Select the rheostat resistance using the slider.
• In the case of other cells, you can select the emf of the first and second cells using the slider.
• To see the circuit diagram, click on the ‘Show circuit diagram’ check box seen inside the simulator window.
• Connections can be made as seen in the circuit diagram by clicking and dragging the mouse form one connecting terminal to the other connecting terminal of the devices to be connected.
• Once all connections are made, click and drag the one way key to insert it into the switch.
• Drag the plug and insert it in the first gap of the two way key.
• Slide the jockey along the potentiometer wire to obtain the null point.
• You can see the first balancing length in the popup.
• Now drag the plug and insert it in the second gap of the two way key.
• Slide the jockey along the potentiometer wire to obtain the null point.
• You can see the second balancing length in the popup.
• You can compare the emf values of the two cells using the value of first and second resonating lengths.
• You can repeat the experiment by increasing the current by adjusting the rheostat.
• To verify your result click on the ‘Show result’ check box.
• To redo the experiment, click on the ‘Reset’ button.

# Observations

 No. Ammeter reading (A) Balancing length when $\dpi{100} \frac{E_1}{E_2}=\frac{l_1}{l_2}$ E1 in the circuit, l1 (cm) E2 in the circuit, l2 (cm) 1 2 3 4 5 6

# Calculations

Calculate the ratio of E1 and E2 for each set of l1 and l2. The mean of the calculated values gives the ratio of emf’s of the two given primary cells.

# Result

The emf’s of the two given primary cells are compared.

The ratio of emf’s of the two given primary cells, E1/E2 = ..............

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