Potentiometric voltmeter

Posted on Feb 5, 2014

The potentiometer value is not critical: anything from 1 k © to 100 k © is acceptable. If you have built the `precision potentiometer` described earlier in this chapter, it is recommended that you use it in this experiment. Likewise, the actual values of the resistors are not critical. In this particular experiment, the greater the value, the bett

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er the results. They need not be precisely equal value, either. If you have not yet built the sensitive voltage detector, it is recommended that you build one before proceeding with this experiment! It is a very useful, yet simple, piece of test equipment that you should not be without. You can use a digital multimeter set to the "DC millivolt" (DC mV) range in lieu of a voltage detector, but the headphone-based voltage detector is more appropriate because it demonstrates how you can make precise voltage measurements without using expensive or advanced meter equipment. I recommend using your home-made multimeter for the same reason, although any voltmeter will suffice for this experiment. Build the two-resistor voltage divider circuit shown on the left of the schematic diagram and of the illustration. If the two high-value resistors are of equal value, the battery`s voltage should be split in half, with approximately 3 volts dropped across each resistor. Measure the battery voltage directly with a voltmeter, then measure each resistor`s voltage drop. Do you notice anything unusual about the voltmeter`s readings Normally, series voltage drops add to equal the total applied voltage, but in this case you will notice a serious discrepancy. Is Kirchhoff`s Voltage Law untrue Is this an exception to one of the most fundamental laws of electric circuits No! What is happening is this: when you connect a voltmeter across either...

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