.

**Procedure and questions**

- Access the
**PhET**web site. - Click on
**Simulations**. - From the left hand menu pick
**Electricity, Magnets, and Circuits**. - Choose
**Circuit Construction Kit: DC & AC (Direct Current & Alternating Current)** - Build a RC circuit with battery 30V, Resistance 10 Ohms y Capacitance 0,12 Farads
- Charge the capacitor by closing the switch on the left.

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

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

- What happens to the amount of charge on the capacitor as time goes on? How long does the capacitor take to charge?

- Now discharge the capacitor by opening the switch. Sketch the graphs of Voltage vs. Time for the resistor and the capacitor below.

- What happens to the current

through the circuit as time goes on?

- What happens to the amount of

charge on the capacitor as time

goes on? How long does the capacitor take to discharge?

- 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.

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

- 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.

- Right click on the capacitor and increase the capacitance. Use another color to show the results on your charging and discharging graphs above.
- What happens to the current through the circuit as time goes on?

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

- 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?

- 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?

- Take different combinations of R and C and measure the charging time and the corresponding time constants.

R | C | Time | Time constant |

- Does your measured time constant agree with the theoretical prediction?

- Take to capacitors and one resistor, connect them in series and in parallel and evaluate the differences on the charging time. R=

C1= C2= | Time | Time constant |

Series | ||

Parallel |

- What is the specific event that the time constant measures? Use the charging equation to show that the time constant equals RC.