AP Physics C Lab: Kirchhoff’s Rules and Multiloop Circuits
1. Examine the resistors. The colored bands on composition resistors conform to a color code that
gives the resistance value and the tolerance. Look up the color code in the table provided and
identify the value of each resistor. The actual resistance may vary according to the tolerance
indicated by the last band: red = ±2%, gold = ±5%, silver = ±10%, no band = ±20%.
2. Connect the two-loop circuit a shown in the diagram below. Law out the components on the
table as shown in the diagram. Leave the switches open until the circuit is checked by your
instructor. If you are using variable output power supplies leave them on the lowest output
setting until you are ready to begin taking measurements.
3. After your circuit has been checked, close the switches and using a voltmeter, adjust the output
voltages to the approximate values shown on the diagram and record their measured values in a
data table. Do not exceed the recommended voltages. Follow proper precautions (type of circuit
connection, polarity, maximum value) when using the voltmeter.
4. Temporarily open the switches. Insert the ammeter in series with one of the branches. Close the
switches, measure and record the branch current, then open the switches. Caution: The
ammeter must be connected in series and with the proper polarity. Start with the highest
maximum, least sensitive scale and move to more sensitive input if possible for the most
accurate reading.
5. Repeat the current measurement for each of the branches.
6. Connect the three-loop circuit as shown in the diagram below. Follow the same procedure and
precautions for this circuit as you did for the first circuit. Measure the operating voltages of the
power supplies and each branch current and record in a suitable data table.
7. For the two-loop circuit, designate current directions for each current and show on a diagram.
Write two loop equations and one junction (black dot in the diagram) equation. Solve the
equations for the theoretical values for the three branch currents. Show your work. If you use a
matrix method, show the content of your matrices you used.
8. For the three-loop circuit, follow the same procedure to solve for the five branch currents by
writing three loop equations and two junction equations. Show your work and any matrices
used.
9. Calculate the percent error for each current and place in the data table.
10. The ammeters used in this lab have a resistance of 10.2 ohms when set to the 0.05A scale and
about 1.4 ohms when set to the 0.50A scale. What percent error might the ammeter resistance
cause in the two-loop circuit when reading the current through R3?
11. How does this error compare with the resistor tolerance noted earlier in the exercise?
R3=220
R2=1k
R3=680
V1=6V
R1=470
R4=330
V2=12V
R1=150
V1=6V
R2=100
R5=680
V2=12V
AP Physics C Lab: Kirchhoff’s Rules and Multiloop Circuits
Resistor Color Code
Find tolerance band and place on the right. Read code left to right. First two bands give significant digits
of resistance value, third band is a multiplier—its color gives exponent of ten. Example: red, red, orange
gold gives 22 x 103 ±
Black Brown Red Orange Yellow Green Blue Violet Grey White 5%
0
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