SP212 Lab: Five Kirchhoff’s Rules
Version: February 20, 2015
PHYSICS II
LAB 5
SP212
Kirchhoff’sRulesandRCCircuitsPre‐Lab
Section 1- Multi-loop Circuit.
1. Read Sections 27.1-27.3 of your textbook.
2. A multi-loop circuit is shown below. We will use Kirchhoff’s rules to determine the
currents (i1, i2, and i3) passing through the three ammeters below. Note the directions
defined below to represent positive current: at least one of the currents must be negative!
Write down two Kirchhoff’s loop rule (or Kirchhoff’s voltage law) equations using the
unknown currents that describe this circuit.
3. Write down one Kirchhoff’s junction rule (or Kirchhoff’s current law) that describes this
circuit using the unknown currents.
4. Solve these three simultaneous equations to determine the value for each of the three
currents.
i1=
i2=
i3=
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Version: February 20, 2015
Section 2- Resistors in Series and Parallel.
1. You have two resistors, with resistances R1 and R2. Assume that R2 is larger than R1. These two
resistors are connected in parallel.
a. Sketch this resistor network below.
b. You measure the equivalent resistance to be Req. Which of the following is correct?
(a) Req is smaller than either R1 or R2.
(b) Req is larger than R1 but smaller than R2.
(c) Req is larger than either R1 or R2.
(d) We don’t have enough information to determine this yet.
c. Now resistors R1 and R2 are connected in series. Sketch this resistor network below.
d. You measure the equivalent resistance to be Req. Which of the following is correct?
(a) Req is smaller than either R1 or R2.
(b) Req is larger than R1 but smaller than R2.
(c) Req is larger than either R1 or R2.
(d) We don’t have enough information to determine this yet.
2. What is the equivalent resistance between points A and B in the figure below?
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Version: February 20, 2015
Section 3- Kirchhoff’s Junction Rule.
What will be the reading in each of the three ideal ammeters at right?
i1=
i2=
i3=
Section 4- Resistors and Batteries in Series and Parallel.
In the following circuits, all batteries are identical and ideal. Also, all light bulbs are identical.
Rank the circuits according to the brightest light bulb? (The brightest light bulb will be the one
with the most current flowing through it.)
Explain why:
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Version: February 20, 2015
Section 5 - RC circuit.
1. Read Section 27.4 of your textbook. Consider this RC circuit.
2. The switch has been in position 1 for a very long time. At time t=0, the switch is moved
to position 2. At t=4.0 s, what is the magnitude of the current read by the ammeter?
3. The switch has been in position 2 for a very long time, so that the capacitor is completely
discharged. At time t=0, the switch is moved to position 1. DRAW the values read by
the ammeter and voltmeter as a function of time. Note the signs.
4. The switch has been in position 1 for a very long time, so that the capacitor is completely
charged. At time t=0, the switch is moved to position 2. DRAW the values read by the
ammeter and voltmeter as a function of time. Note the signs.
Page 4 of 5 SP212 Lab: Five Kirchhoff’s Rules
Version: February 20, 2015
AppendixA
SequenceofbuttonpushesforyourTItosolve3equations3unknownsis(althoughanycollege
studentshouldbeabletosolvethismanually):
1) Menu 2) 3 for “Algebra” 3) 7 for “Solve System of Equations” 4) 1 for “Solve System of Equations” 5) Set number of equations to 3 6) Set variables to “x,y,z” Page 5 of 5