phys 351 lab 3

phys 351 lab 3 - Observations Section A: Impedances A-1,...

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Observations Section A: Impedances A-1, Two Resistors In section A=1, circuit A, a voltage source connected with a resistor in series was created. A second circuit, circuit B was created, containing just a resistor. The two circuits were not connected. The output voltage of circuit A is just Va. The input voltage of circuit b is 0. With the two circuits connected, the output voltage of circuit A is the input voltage of circuit B. A-2, Measuring R Th of the Function Generator In section A-2, the R Th of the function generator was found by connecting the function generator into a resistor substitution box. Therefore it is observed that the resistor of the function generator and the resistor of the resistor substitution box are added in series with one another. The voltage amplitude of the output function was observed on the oscilloscope to note any changes in amplitude. The input was a 1.08Volt peak to peak. The resistance on the substitution box was changed until there was an observed change in the output voltage of the generator. With a resistance value of 150Ohms, the output voltage dropped to 780mV. With a resistance value of 47Ohms, output voltage dropped to 500mV, approximately ½ of the original output voltage.
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Circuit in A-2 A-3, Measuring the Input Resistance of the VOM In section A-3, a simpsons VOM was used in order to find the input resistance. Using a similar method as the one in section A-2, the input resistance was measured. The voltmeter is set to read a 10 VDC full scale, and a DC voltage source is used to power the circuit. A resistance is provided, in this case a resistance substitution box, as before. Measurements were made, and recorded until the voltage dropped to about ½. At this point, we recorded the resistance. Next we lowered the VOM to a 50V DC range. Going through the same procedure, the resistance was once again recorded, this time with less accuracy. Circuit A-3 A-4, Oscilloscope Input Resistance In section A-4, using a 100Hz sine wave as the applied voltage, rather than a DC voltage, we hooked the scope up in series with a resistor and the voltage source. Resistance on the substitution boxed started off small, and steadily increased. Measurements were taken until the output voltage dropped by ½. At
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this point it was observed that the oscilloscopes measurements became very poorly read due to the increased resistance of the substitution box’s resistance. Circuit A-4 Section B: Filter Design- know your impedances B-1, Low Pass Filter In this section, a low pass filter is built. In the initial circuit, it is found that using the arbitrarily chosen values of R and C, that the filter output did not fall by 3 dB at the desired frequency. A better choice for R and C were used to replace the initial pieces used. A new circuit was built and the roll-off was found for the
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This note was uploaded on 11/03/2009 for the course PHYS 351 taught by Professor Staff during the Spring '08 term at UNC.

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phys 351 lab 3 - Observations Section A: Impedances A-1,...

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