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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 low-pass and high pass-filters, 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. Low-pass Filter: Here the circuit shown in figure-1 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, low-pass 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 graph-1 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 = (graph-2), 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 graph-3. 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 graph-4. 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