Experimental Determination of Cell

The emf of a cell is measured with the held of a potentiometer. The principle involved can be clearly understood fi-om Fig 1.1 

AB is the potentiometer slide wire of a rmiform cross section and having a high resistance. A storage cell C is connected, across the terminals of the slide wire AB, such that potential drops from A to B. Now the cell X whose emf. is required is connected to A so that its emf opposes that of C . 

This means that the emf of cell X just balances the drop of potential between A and P. Next a standard cell (S) is taken to replace the cell X and the experiment is repeated. The emf of the cell S now opposes that of C in the slide wire. Let the contact point, now be Q when there would not be any deflection in the galvanometer. 

This means the drop of potential in the slide wire finm A to Q just balances the emf of the standard cell. 

the wire is of uniform cross section, the two lengths being known and since E, (the emf of the standard cell) is known, E can easily be determined. 

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W. Olthuis, W. Steekstra, P. Bergveld, Theoretical and experimental determination of cell constants of planar-interdigitated electrolyte conductivity sensors, Sens. Act. B Chem.,1995, 24-25, pp. 252-256. 

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