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Unformatted text preview: Matt Weiner Phys. 241 10/17/06 Lab 8 Capacitors and RC Circuits Part II: AC Response Goal: The goal of this lab is to further investigate how capacitors act in electrical circuits. Also we will look at circuits with time varying applied voltages. We will also measure the capacitance and impedance. Theory: When dealing with a capacitor with a resistance is called the capacitive reactance or the impedance. The impedance is shown as X c . The unit for reactance or impedance is the ohm. The ratio of the peak voltage and the capacitor is as follows: PEAK PEAK c I V X = (1) The peak voltage is measured by the oscilloscope by reading the graph. Also we use the equation (V=IR). When reading the sine wave of a resistor on the oscilloscope there is a peak applied voltage ( V R,0 ) and the peak current ( I R,0 ). These occur at the same time and can be expressed as a ratio V R,0 / I R,0 this ratio gives us the resistance, R . For a capacitor we observe the same peak I I,0 and V I,0 and the ratio V I,0 / I I,0 gives us the impedance, X c . C I V X C C c ϖ 1 , , = = (2) This gives us another method of solving for the capacitance, C . Once we find the peak current and voltage, we make a plot of X c vs. 1/ω. The slop of the line is equal to 1/C. equal to 1/C....
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