Purpose: Use this simulation to observe changes that occur in a circuit as time passes.

a. Observe changes in the current during charging and discharging.

b. Observe changes in the voltage across a resistor during charging and discharging.

c. Observe changes in the voltage across a capacitor during charging and discharging.

Procedure and questions

1. Access the PhET web site.

2. Click on Simulations.

3. From the left hand menu pick Electricity, Magnets, and Circuits.

4. Choose Circuit Construction Kit: DC & AC (Direct Current & Alternating Current)

5. Select Upload and navigate to the Teacher's Directory to find the file I stored as R-C Circuit Simulation. It should look like the screen picture shown below. You may have to replace the red and black voltmeter connections to the proper location in the circuit.

a. Charge the capacitor by closing the switch on the left.

Sketch the graphs of Voltage vs. Time for the resistor and the capacitor below.

b. What happens to the current through the circuit as time goes on?

c. What happens to the amount of charge on the capacitor as time goes on?

d. Now discharge the capacitor by opening the switch on the left and closing the switch on the right. Sketch the graphs of Voltage vs. Time for the resistor and the capacitor below.

e. What happens to the current through the circuit as time goes on?

f. What happens to the amount of charge on the capacitor as time goes on?

g. Predict the changes to the graphs if the amount of resistance increases by drawing additional lines on your graphs above. Explain the reasons for your predictions.

h. Right click on the resistor and increase the resistance. Use another color to show the results on your charging and discharging graphs above.

i. Predict the changes to the graphs if the amount of capacitance increases. Use the graphs drawn below to show the original graphs and the changes that you predict. Explain the reasons for your predictions.

j. Right click on the capacitor and increase the capacitance. Use another color to show the results on your charging and discharging graphs above.

k. What happens to the current through the circuit as time goes on?

l. What happens to the amount of charge on the capacitor as time goes on?

m. What is the function of a resistor in a circuit? How does it affect the amount of charge that flows? How does it affect the rate at which charge flows? How does it affect the initial and final voltage across the capacitor?

1. What is the function of a capacitor in a circuit? How does it affect the amount of charge that flows?

How does it affect the rate at which charge flows? How does it affect the initial and final voltage across the resistor? How does the capacitor make charge move when there is no battery in the circuit?