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Electricity and Magnetism

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Experiment to illustrate the principle of operation of the Potentiometer

1. Set up a variable potential divider circuit as shown below.


figure 1
Read the voltmeter with the sliding contact, S, at different positions.

Results
Distance of s from X Voltmeter Reading

zero

  

(XY)/4

  

(XY)/2

  

3(XY)/4

  

XY

  

Conclusion
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2.  Measure the voltage of a battery ("battery A" in the diagram below). Let this voltage be V1.

Voltage V1 = __________ volts
. With the circuit above, adjust the position of S so that the voltmeter indicates a voltage equal to V1.
Leave S in this position but change the circuit to the one shown in the figure 2.

figure 2
a) The bulb does not light because
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b) Move S to X. The bulb lights. Which supply is lighting the bulb, battery A or the 6v supply?

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c) Move S to Y. The bulb lights. Which supply is now lighting the bulb?

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The circuits used in this experiment are called potential divider circuits. A POTENTIOMETER is a form of potential divider which can be used to measure an unknown voltage by comparing it with a known voltage. In its simplest form, a potentiometer consists of a piece of resistance wire of uniform cross-section about 1m long, mounted on a support with a linear scale placed near it.

 

© David Hoult 2008