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How do I connect (which wire to which terminal) a four way key to a Potentiometer to compare the EMF of two cells. Circuit diagram and a four wayway key is shown in the pictures.

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Make the connections as below. Here the dots are the connection points and cross-marks are the key knobs.

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When you want to measure the deflections on the galvanometer produced by $E_1$, remove the middle knob of the path along $E_2$. By removing a key knob, you are leaving it in an open circuit, and hence no current passes through. If you want to measure the deflections due to $E_2$, then remove the middle knob in $E_1$.

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  • $\begingroup$ But where do I connect the potentiometer and the galvanometer? And what do you mean by output e1 and output e2 $\endgroup$ – Febin .K.Dominic Feb 14 at 11:42
  • $\begingroup$ The output of E here means the connection between the switch and the galvanometer. As to the potentiometer (assuming you are using a wooden board with the wires arranged as you have shown in the diagram), the wire is attached to the input port (a metal port at one end of the wire). Tie the rest of the wires around that same port - I.e. from the other batteries you’re comparing the end for (or electrolytes). $\endgroup$ – KV18 Feb 14 at 16:53
  • $\begingroup$ you are a life-saver dude. I'm eternally in your debt. I have practics tomorrow and its 11:00 pm. You saved me $\endgroup$ – Febin .K.Dominic Feb 14 at 17:38
  • $\begingroup$ All the best! :) $\endgroup$ – KV18 Feb 14 at 18:00

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