Direct Measurement RC Circuits

• 1. You will be creating a circuit with a battery, resistor, and capacitor in series.  You will be measuring the relationship between current and time as the capacitor goes from zero charge to full charge.  

  2. You will also be measuring the voltage as a function of time for the charging capacitor.  It is possible to do these simultaneously with current.  

  3. Discuss with your team the available tools that can be used to make measurements.  Decide how best to measure current and time.

  4. Write a list of procedures you will follow.  Include at least three trials of different resistances, at least three trials of different capacitances, and at least three trials with different voltage batteries.  

  5. Collect your data.  

Analysis:  

• 1. Graph current vs time for a charging capacitor for each set of data.  Is the shape of your graph linear, polynomial, exponential, inverse?

  2. How does increasing the resistance of the circuit affect your graphs?  Discuss both current and voltage over time.  

  3. How does increasing the capacitance of the circuit affect your graphs?  Discuss both current and voltage over time.  

  4. How does increasing the voltage of the battery affect your graphs?  Discuss both current and voltage over time. 

Discharging a Capacitor

• 1. You will need to start with a fully charged capacitor.  Disconnect it from the battery and connect the positive plate of the capacitor, through a resistor, to the negative plate of the capacitor.  You will be measuring the relationship between current and time as the capacitor discharges.  You will also be measuring voltage over time.  It is possible to measure these simultaneously.  

  2. Discuss with your team the available tools that can be used to make measurements.  Decide how best to measure current and time.

  3. Write a list of procedures you will follow.  Include at least three trials of different resistances and at least three trials of different capacitances.  

  4. Collect your data.  

Analysis:  

• 1. Graph current vs time for a discharging capacitor.  Is the shape of your graph linear, polynomial, exponential, inverse?

  2. How does increasing the resistance of the circuit affect your graphs?  Discuss both current and voltage over time.  

  3. How does increasing the capacitance of the circuit affect your graphs?  Discuss both current and voltage over time.  

  4. Write a brief conclusion paragraph where you discuss the flow of current and the voltage across each element while charging and discharging a capacitor.