# What is

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```					2011 AP Physics

RC Lab
I have a real Charge in Store for you
Background
Two Capacitors will be tested to measure and observe their behavior as they are charged in an electrical
circuit consisting of the capacitor, a power source, resistor and switch. By their nature, capacitors store
electric charge, so be vigilant that you and your lab partners do not get shocked.
Equipment Needed
Power Supply                                                    Logger Pro (Voltage sensor)

Resistor                                                      Multimeter

On/Off Switch                                    Capacitor 2- 100μF and 1000μF (which is directional!)

Process
A. Measure the resistance of the resistor using your multimeter. Turn the dial to the Ohm (Ω)
setting and place the red and black leads on opposite sides of the resistor. Record results on the
data page.
B. Set up the experiment as follows:
a. Connect the power supply, resistor, switch and capacitor in series (should be already
done).
b. Connect the voltage sensor to the Logger pro and in parallel with the capacitor (should
c. Check if the capacitor has a polarity to it- ensure it is wired into the circuit such that the
polarity is correctly matched. (On the yellow capacitors there is a positive side)
d. Open Logger Pro on your computer.
2011 AP Physics

C. Keep Hands away from Bare Metal during this lab, especially when you discharge the capacitor
in step 13.

Procedure:
1. Make sure your Power supply is Off.
2. Start with the small blue Capacitor already wired into circuit.
3. Be sure that the Voltage sensor is connected across the capacitor.
4. Resistor needs to be in series with the capacitor, switch and voltage source
5. Make sure that the switch is open.
6. Turn the Power Supply on and set it to 9 volts.
7. Verify that the Logger Pro is Zeroed and ready (green box should be available to collect data, if
not click on experiment/ connect interface/Lab Pro/Com 1)
8. Use the multimeter to measure the voltage across the power supply (turn the dial to voltage
with a straight line above the V (V) and place red and black leads across the red and black leads
coming out of power supply. Note this must be metal to metal)
9. Collect data by selecting Collect (green box).
10. When the computer has started to plot data close the switch to complete the circuit
11. Observe the Voltage graph on the Screen rising to a constant value,(hopefully matching the
voltage of the power supply)
12. Once Data is no longer being collected, open the Switch.
13. Use Logger Pro to fit an appropriate equation for the graph (click on curve fit, choose an
appropriate equation) and record the equation on your data sheet.
14. Release the charge on the Capacitor by touching the two metal wires on either side with an
insulated wire (not your fingers!) You can even take the capacitor out and touch the two metal
wires to each other
15. Repeat the process from step 4 to step 14 but this time measure the voltage across the resistor.
To measure the voltage across the resistor : move the voltage sensor so that the black connector
is on one side and the red connector is on the other. In other words place the voltage sensor
across the resistor. Remember to fit an appropriate equation for the graph and record it on
16. Change out the capacitor, inserting the Yellow one
 Watch that the positive lead (red hole on power supply) is connected to the positive end of
this capacitor!
 Change the time scale on Logger Pro to a max of 35 seconds by clicking on the x axis and
change the last number to 35.
 Repeat the steps 4-14 to determine the equation for the voltage across the capacitor as a
function of time and the voltage across the resistor as a function of time.
2011 AP Physics

Data Recording
Collect the following for both Capacitors
Resistor stated value(use colored bands to decode) ______________

Measured Resistance (using multimeter) _______________

Voltage across the Power       Equation for Voltage across the capacitor as a
Supply (measured)              function of time

Blue capacitor

Yellow capacitor

Voltage across the Power       Equation for Voltage across the resistor as a function
Supply (measured)              of time

Blue capacitor

Yellow capacitor

What is Maximum Potential across the blue capacitor (look at A and B values of curve fit)?

Determine the capacitance of the blue Capacitor using your voltage across the capacitor as a function
of time equation (remember the time constant = RC):

What is % error of Capacitor value (theoretical value is on capacitor) __________
2011 AP Physics

What is Maximum Potential across the yellow capacitor (look at A and B values of curve fit)?

Determine the capacitance of the yellow Capacitor using your voltage across the capacitor as a
function of time equation (remember the time constant = RC):

What is % error of Capacitor value (theoretical value is on capacitor) __________

Analysis
Fill in the blanks, Show calculations. Where a narrative answer is implied, provide complete sentences.
1. What is % error of the resistance value? _____________

2. Does the measured resistance fall within the error band (last on resistor)? ____________

3. Divide the equation for the voltage across the resistor (both times) by the resistance of the
resistor as a function of time. What quantity does this new equation equal as a function of
time?
2011 AP Physics

4.   Integrate the two equations from #3 as a function of time. What physics quantity does this
equation equal as a function of time?

5. Multiply the voltage as a function of time across both capacitors by the capacitance of the
relevant capacitor.

6. What is the physics interpretation of this equation (describe what this value tells us)?
2011 AP Physics

7. What is the Qmax flowing through the Resistor? Blue__________, Y______________

8. What is the Qmax on the Capacitor? Blue___________,_Y_______________

9. Compare the Qmax values for both the Resistor and the Capacitor. Are they the same?

10. What is the % difference of these two values? B__________,Y_____________

Rubric:
Cover page               8 pts
Data Recording           32 pts
Analysis                 40 pts

Individual Lab Reports

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