Why Do Some Voltmeters Not Show 10V at Full Scale on a Potentiometer?

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The discussion centers on an experiment measuring voltage across a potentiometer connected to a 10V DC supply, using five voltmeters with different internal resistances. The voltmeter with the highest internal resistance, around 10 megohms, is identified as producing a straight line on the graph, indicating accurate voltage readings. Some voltmeters did not read 10V at full rotation due to their lower input impedance, which can cause voltage drops when measuring. Additionally, the resistance between the potentiometer wiper and the clockwise contact can affect readings, as it is unlikely to be zero ohms. Understanding these factors is crucial for accurate voltage measurements in potentiometer applications.
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The attached graph shows an experiment I performed where I had a potentiometer connected to a DC 10V supply, the voltage across the pot was measured with 5 different voltmeters of varying internal resistance. I guess the one with the highest internal resistance, to the order of 10megohm, is the straight line, v2, am I right in thinking this?

Can anyone tell me why some of the voltmeters didnt read 10V at 100% rotation?
 

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a3sportback54 said:
The attached graph shows an experiment I performed where I had a potentiometer connected to a DC 10V supply, the voltage across the pot was measured with 5 different voltmeters of varying internal resistance. I guess the one with the highest internal resistance, to the order of 10megohm, is the straight line, v2, am I right in thinking this?

Can anyone tell me why some of the voltmeters didnt read 10V at 100% rotation?

Did you measure the resistance between the wiper and the CW contact? If it's not zero Ohms (probably isn't), then your lower-input-impedance voltmeters may still cause a voltage drop at full CW...
 

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