Introduction: This experiment will help study the effects of non-ideal voltage meters. We will first calculate the measured output voltage when using an ideal voltmeter with infinite resistance. We will then be using an Analog Discovery and a Digital Multi-meter to measure the voltages across a resistor. Comparing the results with the theoretical calculation of an ideal measurement will help us understand how internal resistance of voltmeters affects data collection.
Above is the drawing of the circuit we used, as well as the work for our prelab. Part A shows an ideal voltmeter with infinite resistance resulting in an output of 2.5 V. Part B shows an ideal voltmeter with an internal resistance Rm of 10,000,000 Ohms, which results in an output of 1.65 V.
Above is a picture of our circuit, which is consisted of 1 wire inputting 5 Volts from the Analog Discovery, two 10,000,000 Ohm resistors, and two probes measuring the voltage across the second resistor. The resulting output voltage was around 1.65 V.
Above is a picture of measurement of the voltage by using the Analog Discovery as a voltmeter, and a setup involving 2 10,000 Ohm resistors. The resulting output voltage was 2.39 V.
Above is a picture of my calculations of the internal resistances of the digital voltmeter and the Analog Discovery. The Rm of the DMM came out to 10,060, 240.9 Ohms, which is approximately 10M Ohms. However, the Rm of the Analog Discovery only came out to 108,624, which is approximately 100K ohms. This is the reason we used different resistors for the DMM and the Analog Discovery, since we were informed that the internal resistance of the DMM would be much higher than that of the Analog Discovery, and we wanted to avoid skewed data.
Since the internal resistance of the DMM was so high, the output of the voltage was also a lot lower than it would have been with an ideal voltmeter.
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