Report for Experiment #18
RC Circuits
Maia Li
Lab Partner: Danielle Pucciarelli
TA: Maksim Piskunov
June 31, 2017Introduction
In this experiment, we set up a simple RC circuit and studied its currents and voltages
...
Report for Experiment #18
RC Circuits
Maia Li
Lab Partner: Danielle Pucciarelli
TA: Maksim Piskunov
June 31, 2017Introduction
In this experiment, we set up a simple RC circuit and studied its currents and voltages and how
they changed over time. Using this data, we were able to determine the time constant of the circuit. In
investigation 1, we set up an uncharged capacitor, power supply, switch, and resistor in series.
Immediately after flipping the switch, we measured the voltage over time – first over the resistor, and then
over the capacitor. After plotting these graphs with logarithmic fits, we could calculate the time constant.
In investigation 2, we set up a circuit with a switch so that when switched one way, it would charge the
capacitor (power supply and a smaller resistor), and switching it the other way would discharge the
capacitor (1 kΩ resistor). After fully charging it, we flipped the switch and immediately began to measure
the current through the capacitor over time. With these values plotted and fitted, we could find the time
constant. Lastly, in investigation 3, we connected two capacitors in series with a resistor, switch, and
power supply. Upon closing the switch, we measured the voltage over the resistor, and found that the
voltage dropped to 0 nearly instantly. We then set up the two capacitors in parallel, measured the voltage
over the resistor over time, and found the new time constant. Ultimately, we learned about the relationship
between time and RC circuits – how voltage and current change over a capacitor and resistor as the
capacitor charges or discharges.
Investigation 1
Set up and Procedure
For investigation 1, we used a .1 F capacitor, 1 kΩ resistor, a switch, a power supply, and a
multimeter. We connected the components in series, and used the multimeter to more accurately set the
power supply to 6V. During this and all future investigations, we kept the multimeter on the automatic
setting. We checked to make sure the capacitor was discharged, by connecting it in a loop with a 10Ω
resistor. We connected the voltmeter around the resistor for the first part of this investigation We then
closed the switch and immediately began counting time. One team member controlled the voltmeter, and
the other had the timer and Excel table. We took readings for every 10 seconds over 5 minutes. After
gathering our readings, we plotted the voltage over time using a logarithmic fit. The equation of our line
helped us calculate the experimental time constant. We then repeated these steps exactly with the
voltmeter measuring the voltage over the capacitor. We approximated the error in the time to be .05
seconds, based on our average reaction times. The error in voltage is the inherent error of the multimeter.
Figure 1: Circuit diagram of all components in series.
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