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Unformatted text preview: Title: AC Circuits II (RL) Richard Madison Haynie Partner: Joseph Gilgen (All graphs are attached to back) Objective: In this lab the goal is to observe lowpass and high passfilters, how they function and why they function as they do. Once this is done learn how these filters can be used as either a garbage detector and filtering out noise when added to an input signal. Lowpass Filter: Here the circuit shown in figure1 was constructed. From theory the reactance of a capacitor is given by 1 2 C X fC π = which means when f is small X C is large and when f is large X C is small. For this circuit this means when f is small enough in out V V X and when f is infinitely large out V X . Since in out V V X for small frequencies the circuit earns its name, lowpass filter. A low pass filter is a voltage divider and the equation is ( 29 2 2 2 2 1 1 1 2 1 out in V C V fRC R C ϖ π ϖ = = + + . The phase angle can be found using 1 1 tan 90 2 fRC φ π = o . To find the values of f that are small or large enough for our expected results we compute a f 3dB . From theory 3 1 2 dB f RC π = and with this circuit f 3dB =1061Hz. The circuit was then driven with a frequency of 1065Hz and is shown in graph1 with .676 out in V V = from theory .706 out in V V = differing by 4.2% from the experimental value. Next f 3dB is calculated experimentally by finding the frequency for which V out is 70.7% of V in . The value found experimentally was f 3dB =969Hz with .716 out in V V = (graph2), so f 3dB from theory and experimentally are approximately equal differing by 8.7%. The circuit was then driven with 96.98Hz which is much smaller then f 3dB (our small frequency) shown in graph3. Indeed out V V X which expected, from theory .021 out in V V = . The circuit was then driven with 49.36kHz which is much greater then f 3dB (our large frequency) shown in graph4. For this frequency V out is greatly attenuated because V out approaches zero as f approaches infinity which was expected. The approaches zero as f approaches infinity which was expected....
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This note was uploaded on 05/11/2008 for the course PHY 333 taught by Professor Tsong during the Spring '08 term at ASU.
 Spring '08
 Tsong

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