Physics 360 Neumann

Virtual Lab 5: RC Circuits

Name(s): ____________________________________________________________________________ PURPOSE To understand how charge is stored on the capacitor, and how the capacitor charges and discharges over time.

In this circuit, we are going to be dealing with the following circuit. Notice that there are two different resistors (10 Ω and 33 Ω), and two batteries connected in series (each battery is 1.5 V). All the data can be found in the Excel file titled “RC Circuits Data”.

1. Sketch the circuit diagram for this circuit. Notice that the position of the switch is different for charging and

discharging. Part I: Charging and discharging a capacitor 2. Open the Excel file. The first two tabs (Ckt1 and Ckt2) are dealing with charging and discharging the capacitor.

Plot the data for current through the capacitor and for voltage across the capacitor, from both tabs. Use scatterplot option, and do not “connect the dots”. Don’t forget to label the axes (with units), and to label each graph. Use a full-size graph (one graph per page), and choose the appropriate scale for the axis values. When you are done with this lab, do not forget to attach your graphs to your lab report.

3. Ckt1 tab shows the data for the circuit above. Notice that the time constants are different for charging and discharging parts. Calculate the theoretical value of the time constants using the nominal (labeled) values of the capacitance and the resistance. Show work, and don’t forget units.

τth,charging = ____________________ τth,discharging = ___________________

4. Using your graphs, show how to get the time constant from the graph. Note that there are two full charge-

discharge cycles for each graph. Therefore, determine the time constant twice, and report the average value. τgraph,charging = ____________________ τgraph,discharging = ___________________ 5. Calculate %error between theoretical value and measured values, for both charging and discharging. Show

work. 6. Now we switch the two resistors. Ckt2 tab shows the data for this new configuration. Repeat 3-5. Again, notice

that the time constants are different for charging and discharging parts. Calculate the theoretical value of the time constants using the nominal (labeled) values of the capacitance and the resistance. Show work, and don’t forget units.

τth,charging = ____________________ τth,discharging = ___________________ 7. Using your graphs, show how to get the time constant from the graph. Note that there are two full charge-

discharge cycles for each graph. Therefore, determine the time constant twice, and report the average value. τgraph,charging = ____________________ τgraph,discharging = ___________________ 8. Calculate %error between theoretical value and measured values, for both charging and discharging. Show

work.

Part II: Intensity of Lightbulbs 9. The 10 Ω resistor is now replaced with a lightbulb. Watch the short video “OneBulb” and describe qualitatively

what happens with the intensity of the lightbulb. In your explanation, include a description of when/how the current is flowing through the lightbulb, and an explanation of why the intensity is changing the way it is. No equations!

10. Ckt3 tab in the Excel file shows the data for this new configuration. Plot the data for current through the

capacitor and for voltage across the capacitor. Don’t forget to label the axes (with units), and to label each graph. Use a full-size graph (one graph per page), and choose the appropriate scale for the axis values. When you are done with this lab, do not forget to attach your graphs to your lab report.

11. How do these graphs support your explanation in #9? 12. Why do you think the quality of this graph is worse than the quality of the two previous graphs? 13. From the graphs, determine the resistance of the lightbulb. Show work! 14. The 33 Ω resistor is also replaced with a lightbulb. Watch the short videos “TwoBulbs1” and “TwoBulbs2” and

describe qualitatively what happens with the intensity of the two lightbulbs. In your explanation, include a description of when/how the current is flowing through the lightbulb, and an explanation of why the intensity is changing the way it is. No equations!

15. Ckt4 tab in the Excel file shows the data for this new configuration. Plot the data for current through the

capacitor and for voltage across the capacitor. Don’t forget to label the axes (with units), and to label each graph. Use a full-size graph (one graph per page), and choose the appropriate scale for the axis values. When you are done with this lab, do not forget to attach your graphs to your lab report.

16. How do these graphs support your explanation in #15? Don’t forget to attach your three graphs (there should be a total of 8 graphs, with your work shown on them)!

Ckt1