Description
PHYS 2020 Lecture 14 (Laboratory)
Kirchoff’s Laws
Adapted from the University of Sharjah
We did a walkthrough of some problems involving more complex circuits, but it’s a good idea to
reinforce the concept.
Materials (see Appendix):
•
None
Activity 1: Kirchoff’s Current Rule
Since we have limited lab equipment in an online situation, we will be exploring the concepts virtually
using a PhET simulation. Click on the following link to use today’s simulation.
1- Use the DC Power supply, the resistors and the connecting wires provided on the simulation
software to build up the circuit below (if you can’t get the specific values of the resistors, don’t
panic). Confirm you have conventional current turned on.
R1
R2
1
2
R3
2- Change the power supply outputs and the resistor values and observe how the currents change in
response
Think About It:
Can you get a current to go backwards through a battery? What does it take?
3- Connect Ammeters in series with each resistor (as shown below, assume all current directions follow
the loops) to measure the current flowing through each resistor record your values in the table. Note
that your resistors, emfs and currents will be different that shown in the image.
4- Calculate the expected currents for the voltages and resistors of your circuits. Include your work as
an appendix to your report, and compare your results to the simulated values (including an error
assessment assuming the simulated value is correct).
I1
I2
I3
Loop 2
Loop 1
1
2
1 = ………………….
2 = …………………
Experimental results
R (k)
Calculated results
I (mA)
R (k)
Think About It:
Is Kirchhoff’s current law satisfied? How can you tell?
I (mA)
Activity 2: Kirchoff’s Loop Rule
1- Reset the resistors and voltages to new values
2- Connect voltmeters in parallel with each resistor (as shown below for resistor 1) to measure the
voltage drop across it; fill your data for the voltages in the table.
IV1
Think About It:
What happens if you swap the leads from the voltmeter across the resistor? Would it make a
difference in your results?
1 = ………………….
2 = …………………
Experimental results
R (k)
Calculated results
V (V)
R (k)
Think About It:
Is Kirchhoff’s voltage law satisfied? How can you tell?
V (V)
3- Calculate the expected currents for the voltages and resistors of your circuits. Include your work as
an appendix to your report, and compare your results to the simulated values (including an error
assessment assuming the simulated value is correct).
Activity 3: Extra Practice
1- For extra practice on Kirchhoff’s laws, connect the circuit below and do current and voltage
measurements using the ammeter and the voltmeter. Show your findings on the table below.
Experimental results
R (k)
I (mA)
Calculated results
V (volt)
R (k)
1
1
1
1
0.1
0.1
I (mA)
V (volt)
2- Calculate the expected currents for the voltages and resistors of your circuits. Include your work as
an appendix to your report, and compare your results to the simulated values (including an error
assessment assuming the simulated value is correct).
Deliverables
We need an informal report describing what you did and what you learned. Imagine you are talking to
your parents or your boss, and describing the activities you just completed. Make sure to include any
pictures and resulting understanding you have gained. Submit a copy of this report for grading.
Rubric:
Documentation
Missing
25 (0.00%)
Novice
15 (30.00%)
Partial
20 (40.00%)
Proficient
25 (50.00%)
Did not submit
Narrative unclear,
incomplete thoughts
and/or sentences. Did
not include sufficient
information for a person
to replicate the work
Narrative was fairly clear,
but left out something
significant (i.e, meaning
of the results, numbers
without units or
uncertainties)
Ideas were expressed in a
clear and organized
fashion. It was easy to
figure out what was going
on, and how to repeat
the experiment if desired.
Included discussion of
results compared to
accepted values (with
appropriate uncertainties
and units)
A post-lab quiz will also be required to assess your understanding of the goals for this lab, and will count
for half the grade.
Question 1 (1 point)
Which is a correct statement of Kirchhoff’s Loop Law?
a
The sum of currents around any closed loop is zero
The sum of voltages around any closed loop is zero
The total current going into a junction is equal to the total current coming out of
the junction
The total voltage going into a junction is equal to the total voltage coming out of
it
Which is a correct statement of Kirchhoff’s Junction Law?
The sum of currents around any closed loop is zero
The sum of voltages around any closed loop is zero
The total current going into a junction is equal to the total current coming out of
the junction
The total voltage going into a junction is equal to the total voltage coming out of
it
What would be the correct junction law equation for the junction shown below?
13
“T
12
13 = 11 + 12
11 + 13 = 12
11 = 12 + 13
=
11 + 12 + 13 = 0
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