Physics 251 Laboratory
DC Circuits I: Simulation
Introduction
This lab deals with direct-current circuits that consist of different combinations of batteries
and resistors. Specifically, you will be using Kirchoff’s Laws to study two simulated direct-current
circuits. You will use what you have learned about spreadsheets in the previous lab to make
calculations of circuit behavior for various values of these resistances, voltages, etc., in these
circuits.
Equipment/Supplies
Macintosh computer with Microsoft Excel software
Simulations are in the 251 folder in a file labeled: “Kirchoff Simulation.”
Section 1
Open the file “Kirchoff Simulation.” You will see two separate areas, each with its own circuit
diagram, and cells for values of source voltage, relative voltage, resistance, and current. Some of
these cells are already filled in. The ones that are not filled in have a double border. You will need
to write a formula for each of these double-bordered cells that calculates the appropriate value of
relative voltage or current (remember to begin each formula with an “=”).
Look at the first area. It has a diagram of
a circuit consisting of one battery, three
resistors, and an ammeter. The symbol in the
bottom right hand corner is ground ( this
denotes the arbitrarily chosen location where
the voltage is 0).
The source voltage is set at 12 volts (cell
A3). The three resistances are all set at 100
ohms (cells D8,C7,and A8).
Ø Create a formula that will calculate the
current through the circuit, given the
source voltage and the values of the
resistors, and enter this formula in cell
C9.
Ø Test your formula by changing the given values of source voltage and resistance. Do the
values you obtain for the current make sense?
Physics 251 DC Circuits Lab
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Section 2
Continue to work with the first circuit, focusing on the three empty cells available for voltage
calculations (D7,B7, and B9). Create a formula for each of these cells that calculates the voltage
relative to ground at points a, b, and c. These formulas should all depend on the source voltage,
the individual resistance values, and the value of the current.
Ø Again, test your formulas by changing the given values.
Ø Before moving ahead please answer the questions on the back page referring to Section 2.
Section 3
The second area has a circuit that is somewhat more complicated than the previous one. A
branch has been added as well as two additional batteries. There are now three currents present
that you will need to create formulas for (cells H3, I3, and J3). These are the formulas that
you calculated before class and should be in terms of the three source voltages and the three
resistance values.
Ø Once again, test your formulas by varying the values for the source voltages and resistances.
Do your formulas hold up?
Ø Create a few more cells
that calculate other
testable values.
Ø Calculate the voltage
difference between the
bottom wire and the node
at the top-center using
three different paths.
Ø Please answer the
questions on the back
page that refer to Section
3.
Physics 251 DC Circuits Lab
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Physics 251 Laboratory
DC Circuits - 2
Introduction
In this lab, you will set up a real two loop circuit consisting of three resistors and three
batteries. You will use a voltmeter, an ammeter, Ohm’s law and Kirchoff’s laws to find values of
resistance and current.
Equipment/Supplies
3 voltage sources
3 resistors
Wires
Multimeter
Section 1
Use your multimeter to measure the resistances of the three resistors, and the voltages
provided by the three voltage sources. The actual values may differ from the nominal values by
several percent.
Section 2
Now set up a two loop circuit as shown in
the picture, using the three batteries and the three
resistors. Be mindful of the polarity of the
batteries. Be sure your circuit duplicates the one
in the diagram. Using the spreadsheet you
developed last week, calculate the current in each
branch of the circuit, including the direction, as
well as the voltage across each resistor. Record
these values. Now use the multimeter to directly
measure the current and voltage through each
resistor. Do these values agree with the ones you
obtained using Kirchoff’s laws?
Section 3
Use your multimeter to measure the voltages
provided by the three sources without removing
them from the circuit. Do your new values agree with you old values? If not, use your new
values in the spreadsheet, and see if the agreement between calculated and measured currents has
improved.
Physics 251 DC Circuits Lab
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Name ___________________________________ Date _______________________
Lab Partners __________________________________________________________
DC Circuits I - Simulation
Results
Section 2
1. What is the current through the circuit? I:______________________________________
What relative voltages did you obtain for points a, b, and c, using the given values?
V(a):
V(b): ______
V(c):___
2. Now, double the source voltage and halve the value of the first resistor.
What is the current through the circuit? I:______________________________________
What are the relative voltages?
V(a):
V(b):
___
V(c):
___
3. Is there anything unique about any of the relative voltages at point a, b, or c? Why is this so?
_
Section 3
1. What values did you obtain for the three currents, using the given quantities?
I1:
I2:
I3:
2. What is the difference in voltage between the bottom wire and the top/center node, using the
given values?
Physics 251 DC Circuits Lab
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3. Now, change the values of the three resistors to what ever you want and report the currents
again.
R1:
R2:
R3:
I1:
I2:
I3:
Overall – DC Circuits 1
Explain to “the Boss” why we want to use excel to simulate this circuit before we actually build
it? What happens to I1 when we change the value of R1?
__________________
__________________
What was good about this lab and what would you do to improve it?
__________________
__________________
Physics 251 DC Circuits Lab
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Name ___________________________________ Date _______________________
Lab Partners __________________________________________________________
DC Circuits - 2
Results
Section 1
Make these measurements before you build the circuit.
1. What are the measured values of the resistors?
R1_______
R2_______
R3________
2. What are the measured values of the voltage sources?
V1_______
V2_______
V3________
Section 2
Input the above values into your spreadsheet to obtain calculated values.
1. What are the calculated values of current?
I1_______
I2________
I3_________
2. What are the measured values of current?
I1_______
I2________
I3_________
3. What are the calculated values of voltage drop across each resistor?
V(R1)_______
V(R2)_________
V(R3)___________
4. What are the measured values of voltage drop across each resistor?
V(R1)_______
V(R2)_________
V(R3)___________
5. Do the calculated values agree with the directly measured ones?______________
Physics 251 DC Circuits Lab
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Section 3
1. What are the measured values of the voltage sources while they are in the circuit?
V1_______
V2________
V3_________
2.
Use the new values for voltages V1, V2 and V3 in the spreadsheet to calculate current
and voltage drop across R1, R2 and R3
3.
Explain to “the boss” why the measured values of the voltages and currents in the
circuit are different than the calculated values.
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Overall – DC Circuits 2
What was good about this lab and what would you do to improve it?
__________________
__________________
Physics 251 DC Circuits Lab
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Physics 251 Laboratory
Magnetic Fields
Introduction
By now, you have studied methods for calculating the magnetic field due to current
traveling in a wire. In particular, the Biot-Savart law is
r µ0
B=
4π
∫
r
Idl × rˆ
r2
Using this, you can find the magnetic field at the center of a circular, current-carrying wire
loop.
r µ I
B= 0
2R
In this lab, we will observe the effects of such a field, using a compass needle as a detector.
As a final result, we will calculate the magnitude of the horizontal component of the Earth’s
magnetic field, which we will label BEarth,H.
Equipment/Supplies
Glass jar, wooden frame, wire, compass, power supply, ammeter, patch cords and
connectors.
Section 1
Place the compass in the indentation on the wooden frame, and slip the glass jar over the
end of the frame. When you wind the wire in a coil around the jar, you will want the
compass to be located as nearly as possible in the center of the coil.
Your only magnetic field sensor is a compass. The compass is a useful device if you are lost
in the woods, but it can only tell you the direction of a magnetic field. It cannot tell you the
magnitude. We can overcome this difficulty by using the playing the Earth’s magnetic field
and the field of our coil against one another. The compass needle indicates the direction
of the net magnetic field. Describe how to orient your coil on the table in order to create
“contrast” between the Earth’s magnetic field and the coil’s magnetic field. That is, how do
you place the coil such that the Earth’s field and the coil’s field will make the compass point
in different directions. Sketch your apparatus on the results page (indicate which way is
North on your sketch). Also, give an equation which relates the magnitudes of the two fields
(BEarth,H and Bcoil) to the angle between the fields (think trigonometry).
Section 2
Now, wind the coil around the glass jar, and attach it to the power supply. Place your
ammeter (set up to measure large currents) in series with the coil. This will give you a more
accurate measure of the current than the panel meter on the power supply. Wind the coils
close together and centered around the compass. Record the number of loops you made on
the results sheet. How will this affect your results? Write down a formula for the magnetic
field at the center of your coil that includes the number of turns.
To determine BEarth,H you will need to combine your two equations so that you have a single
equation relating the current, diameter and number of turns to the angle θ and BEarth,H.
Then record data. You should do this twice, once varying the current with a fixed number of
coils and once varying the number of coils with a fixed current. Use the tables on the
results page to record your data.
Section 3
Using your data and equation 3, you can now calculate the BEarth,H. By fitting your data to a
straight line. Use excel on the lab computers to plot your data and to fit a line to your data.
How is BEarth,H related to your fit parameters? Please attach your graph and fit data,
including your two calculated values of BEarth,H to the results page when you hand it in.
Name _____________________________________ Date _________________________
Lab Partners _____________________________________________________________
Magnetic Fields
Results
Section 1:
Sketch your apparatus and give your equation relating Bcoil, Bearth and θ the angle between
them. This is your “equation 1”.
Section 2:
Write down an equation for magnetic field strength as a function of the current, the
diameter of the coil and the number of turns. This is your “equation 2”.
Combine “equation 1” and “equation 2” to give a linear relationship between θ, N, R, I and
Bearth . This is your “equation 3”.
Don’t’ forget to attach your graphs and your two values for Bearth
Data:
Number of Coils __________________
θ (degrees)
I (amps)
Current (I) ____________________(Amps)
Number of turns
10°
1
20°
2
25°
3
30°
4
35°
5
40°
6
45°
7
50°
8
60°
9
70°
10
80°
11
θ (degrees)
Explain to “the Boss” how you set up your apparatus and why you set it up that way.
(Specifically the orientation of the coil to magnetic N.)
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
Overall :
What was good about this lab and what could be improved? _____________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
Magnetic Fields Formal Lab Write-up
This report is worth 20 points toward your lab grade (in addition to the regular 10 points
for doing the lab.)
The purpose of the report is to practice writing scientific
papers. When a scientific paper is submitted to a journal for publication or to someone you
work for, it must be written following specific guidelines. Your grade will be determined by
how well you follow the guidelines (5 points), spelling and grammar (5 points) and the
content of the paper (10 points). Any paper that receives a score lower than 15 points will
have the opportunity to be corrected and resubmitted for grading. On the second try – the
maximum score will be 15 points.
Guidelines:
Your paper should include the following headings in the order listed:
Title Page
The title page should include the title of your paper, your name, and the date.
Abstract
The abstract should be a brief summary of your paper (not more than 200 words). Someone
should be able to read your abstract and determine if your paper contains the information
they are interested in reading about.
Introduction
This section should introduce your experiment and what you hope to find out.
Theory
In the theory section should be a derivation of the basic equations you plan to use in the
discussion section as well as how a compass works, something about the earth’s magnetic
field and a discussion of Biot-Savart. It need not be more in depth than what is found in
your book, but please don’t copy from the book without proper acknowledgement.
Methods
Methods section should clearly describe your experiment, equipment and set up. This is
where you will include a picture of the apparatus (section 1 of the lab handout). Someone
should be able to read this section and repeat your experiment without the actual lab
handout.
Results
This is where you include data tables, graphs, calculations and formulas
Discussion
The discussion section is where you discuss the meaning of the results and how they relate
to the theory. This is also where percent error in your measurements is reported.
Conclusion
What was the point of the experiment and did you achieve the results you thought you
would? How could it be improved? What were the error sources and how could they be
minimized.
References
Properly formatted references to any material you used to help you with your write-up.
Minimum would be your textbook.
Actual lab results pages
This is where you attach your actual lab handout for grading. Just the normal stuff you
turn in every week.
Name ________________________
Lecture Section CRN: ______
States of Matter
Learning Goal:
Students will be able to demonstrate their knowledge of the states of matter through illustrations and
descriptions. These illustrations and descriptions should include:
• How the molecules in a solid, liquid and gas compare to each other.
• How temperature relates to the kinetic energy of molecules.
Procedure:
• Open the internet browser and enter the address: https://phet.colorado.edu/en/simulation/states-ofmatter
• Open the “States of Matter” Simulation and select “States”
Investigation:
1. Predict what the molecules of a solid, liquid and gas look like. Illustrate your prediction with a drawing.
Solid
Liquid
Gas
2. Complete the table below by exploring the “Solid, Liquid, Gas” tab in the simulation. Test your
predictions and record your observations by recording the temperature and illustrations of each
substance in the three states of matter.
Substances
Neon
Argon
Observations
Solid
Temperature:
Liquid
Temperature:
Gas
Temperature:
Illustration:
Illustration:
Illustration:
Temperature:
Temperature:
Temperature:
Illustration:
Illustration:
Illustration:
Oxygen
Water
Temperature:
Temperature:
Temperature:
Illustration:
Illustration:
Illustration:
Temperature:
Temperature:
Temperature:
Illustration:
Illustration:
Illustration:
3. Sketch a graph of Kinetic Energy vs. Temperature. Use this graph to describe the relationship between
the two concepts.
4. Write a summary paragraph, which includes drawings, to demonstrate you have mastered the learning
goal. Be sure to incorporate both concepts of the learning goal:
•
•
How the molecules in a solid, liquid and gas compare to each other.
•
How temperature relates to the kinetic energy of molecules.
Open the “States of Matter” Simulation and select “Phase Changes”
5. Explain how a change in temperature affects the pressure inside a container.
6. Explain this phase diagram by relating what you know about temperature, states of matter and
pressure.
...

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