RC circuits & curve fitting Overview: In this lab we will build a DC circuit. Ca
ID: 1543041 • Letter: R
Question
RC circuits & curve fitting
Overview: In this lab we will build a DC circuit. Capacitance and RC time constants will be measured.
Procedure: Create a circuit with a capacitor and resistor in series. Turn the power supply on. After a few seconds turn it off again. Plot the current coming from the power amplifier. Measure and/or fit the exponential curve to extract the RC time constant. Repeat with a different circuit.
Answer the following question. Assume you doing lab with 250 ohm and 500 ohm and 10,000uF capacitor and got a expected result from experiment.
Questions:
1.Is the time constant the same when the circuit is charging and discharing?
2.The combination of a large resistance and small capacitance could have the same time constant as a small resistance and a large capacitance. What, then, are the differences between these possibilities? Give an example of when each would be preferable.
3.How “good” are your fits? What is meant by “goodness of fit?”
Explanation / Answer
The time constant is the product of the capacitance and resistance. It is the same for charging and discharging.
The larger the resistance, the longer it will take for the capacitor to charge or discharge, because the large resistance leads to a smaller current. If the capacitor is large and the resistance is smaller, the capacitor will take longer to charge because of its large value. As long as the time constant is the same, charging as discharging will take the same time irrespective of the value of R and C in different circuits.
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