Physics 102

RC Circuits

March 21, 2006

Eduardo Nunez, Joseph Lan

Abstract: The purpose of this experiment is to quantitatively observe the changing voltages in RC circuits, determine experimentally the validity of Kirchhoff’s Loop Law in an RC circuit, and to determine the ratio V/V0 at R=C.

Equipment:

·  Four resistors (100K, 10K, 1K, and 100Ohms).

·  5µF Capacitor.

·  Power Supply.

·  Computer.

·  Pasco Data Studio with voltage sensors.

Procedure:

1.  Connect the RC circuit using the breadboard.

2.  Use the wire clips and connect to the appropriate leads.

3.  Turn on the battery supply.

4.  Use the Pasco Data Studio Software on the computer to record data.

5.  Wait till the graph on the computer levels off horizontally.

6.  Turn off the battery supply and open the circuit to drain it.

7.  Reconnect the wire clips to a different capacitor.

8.  Repeat steps three to seven for each resistor left.

9.  Take the information from the computer and put into Excel.

Calculations:

Vcap = Vo(0.632)

V/Vo for t = RC

100000Ω(5.0µF) = t

T = .5s

At t = .5s V = 3.154V

V/Vo= 3.154V/6.0V

=0.526

Graphs: (See Excel Spreadsheet).

Error Analysis:

%Error = Theoretical – Experimental X 100

Theoretical

1K Resistor = 6.8%

10K Resistor = 1.7%

100K Resistor = 16.8%

Conclusion:

After concluding this experiment, there were a couple of things we noticed. We were supposed to observe the changing voltages in the RC circuits through the different resistors. We found that our experimental results varied slightly from the theoretical ones. This variation can be due to a series of things; one of them being the second delay on the setup for the computer software. After all we found out that the capacitor become more or less charged when t = RC. Our results show this assumption. Finally it is evident that Kirchhoff’s Law (loop rule) is verified. We can see this through the relationship between capacitor and resistor and their voltage increases and drops.

Questions:

  1. What is the average value V/V0 for each graph at t = RC?

·  1K Ohms graph (V/ V0 = .675)

·  10K Ohms graph (V/ V0 = .636)

·  100K Ohms graph (V/ V0 = .526)

  1. Was Kirchhoff’s Law verified? What might account for variations?

Yes, Kirchhoff’s Law was verified. Even though it was an RC circuit, the loop law still applies as the capacitor becomes charged; the resistor loses some of its voltage, hence the principle of conservation of energy. Some variations found are due to the fact that data studio was set to start recording information after the one second mark. This is one of the reasons for the percent error also.

  1. Describe the charging and discharging voltages curves for the capacitor and resistor in a parallel RC circuit.

This is rather simple to explain. As the capacitor is becoming charged by the battery supply, the resistor starts losing voltage. This can clearly be seen through the various resistors. The graphs clearly depict this. As the voltage increases in the capacitor, the voltage in the resistor decreases accordingly.

Grade = 100