Using a Potentiometer

A potentiometer is a device which allows measurements of potential difference by balancing voltages of opposing polarity. The net voltage across part of the circuit is zero and no current flows. This means that there are no 'stray' voltages or currents making results very accurate in theory. We can use the potentiometer to measure the EMF of a cell using the circuit below.

If then at some point between A and B the potential will be equal toIf the potentiometer wire between A and B is uniform, then the potential at C will be proportion to the distanceWhen the potentiometer contact is at C, the potential difference across AC due toisand this is the voltage across the cell with EMFso that no current flows. We have

These equation assumes that the contacts all have zero resistance and that the potentiometer wire is uniform. These conditions can be closely approached.

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