Download Series and Parallel Circuits - Chabot College Physics Lab

Chabot College Physics Lab
Series & Parallel Circuits
Scott Hildreth
Goals:
 Enhance your understanding of circuits, measuring resistances, currents, and voltages across multiple
components.
 Develop your skills in making “breadboard” connections of electrical components, tracing connection
errors, diagnosing problems, and resolving them logically.
 Verify Kirchoff'’s Rules to solve for current and voltage through series and parallel resistors.
Background:
The previous lab introduced you to making connections on a circuit board, and how to measure current and
voltage digitally using the Vernier equipment and standalone multimeters. Now you will put your
knowledge to a test – of physics, of measurement, and of science. This lab activity will challenge you to
verify Kirchoff’s Rules for circuit analysis in three ways, using the digital measurement devices and
computers as well as theoretically. You will:
a) Design your own arrangement of parallel and series resistors, using two 10, two 51, and two
68 resistors and two power sources (battery and low-voltage external).
b) Use the PhET Circuit Construction Kit online to make a model of your circuit, and test your
hypotheses about the currents and voltages using this model.
c) Use the Vernier circuit boards to actually build your circuit, and measure the values with the
ammeter and multimeter.
d) Solve mathematically for the expected currents and voltages across each resistor using Kirchoff’s
junction and loop rules, to verify that your experimental results are valid solutions.
Write up:
This experimental write up should again follow the formal physics laboratory report format (available
online at http://www.chabotcollege.edu/faculty/shildreth/physics/updated_lab_report_format.htm ). Make
sure that you include the roles that each member of your team played in the activity, clearly labeled
pictures, data tables in your appendix, and answers to the QUESTIONS you’ll find within. The lab report
is due in two weeks from your lab date.
MATERIALS
Computer running Logger Pro software
LabPro interface
Vernier Current & Voltage Probe System
Additional Vernier Voltage Probes
6-8 sets of alligator clip wires
Batteries
adjustable low-voltage DC power supply
Vernier Circuit Board
Digital Multimeter w/ (2) voltage probes
PART A: DESIGN ATHEORETICAL CIRCUIT NETWORK
1. Examine the Vernier Circuit board. Notice that it contains two each of 10, 51, and 68
resistors. You will use these values for the resistors in your theoretical model, the online PhET
model, and actual experimental circuit.
2. For the external power supplies in this lab, you will use one external digital variable low-voltage
power source, and at least one set of batteries (either two C or D cells in the connector, or one 9
volt cell connected externally with alligator clips.)
3. On paper, design your own network of series and parallel connections. Make a large, clearly
labeled sketch of your network, using appropriate symbols. Leave sufficient room in your sketch to
insert (3) values (theoretical, online model, and experimental ) for EACH of the currents and
voltages across each resistor and for each of the power sources).
A sample is provided – but create your own! The constraints you must meet in your design
include:
a. Using all (6) of the resistors.
b. Including at least (4) junctions in your circuit, with both series and parallel elements.
c. Including at least (2) power sources, and ensuring that the power sources are not be
connected in series within just one “leg” of the circuit – there must be at least one junction
between the power sources.
PART B: BUILD A MODEL OF YOUR CIRCUIT NETWORK ONLINE
4. Using the PhET simulator “Circuit Construction Kit – DC Only” available online at
http://phet.colorado.edu/en/simulation/circuit-construction-kit-dc , make a model of your network.
Using the selection boxes available, check:
a. VISUAL: Schematic and Show Values
b. ADVANCED: Hide Electrons
5. Right-click on the individual voltage and resistor icons, and adjust their values to match your
particular design. Save your circuit design once it is complete with a team name.
6. Use the voltmeter and non-contact ammeter tools in the simulator to measure the voltage and
current across all circuit elements (resistors and batteries). Record these online model values on
your sketch.
PART C: TEST YOUR MODEL EXPERIMENTALLY
7. Open the Ohm’s Law file in the Experiment folder of Physics with Computers. A graph of potential
vs. current will be displayed. The vertical axis is scaled from 0 to 6 V. The horizontal axis is scaled
from 0 to 0.6 A. The Meter window displays potential and current readings.
8. Connect DIN 1 on the Dual Channel Amplifier to Channel 1 on the LabPro. Connect DIN 2 to
Channel 2. Connect a Voltage Probe to PROBE 1 on the Dual Channel Amplifier. Connect a Current
Probe to PROBE 2.
9. With the external power supply turned off, connect the power supply, batteries, resistors, wires, and
clips to match your design. Take care that the positive lead from the power supply and the red
terminal from the Current & Voltage Probe are connected correctly.
Note: The circuit board only allows you to direct either the external power supply OR the batteries
to the board at once through the slide switch SW1. If you use the internal battery holder as one of
your sources, you’ll need to connect the external power supply separately using additional wiures
and alligator clips.
10. Click
. A dialog box will appear. Click
current flowing and with no voltage applied.
. This sets the zero for both probes with no
11. Collect experimental data for the voltages and currents through each resistor. For voltage
measurements, you can use the multimeter and/or the Vernier voltage probes. For current
measurements, you’ll need to make sure that the current probe is connected in series with the
appropriate leg of the circuit.
Record your experimental values for the currents and voltages on your original sketch. Include
appropriate significant figures. Include appropriate uncertainties as well!
PART D: VALIDATE YOUR MODEL THEORETICALLY
12. On your paper sketch, identify the currents I1, I2, I3, etc. through each leg of your circuit. Create
the appropriate current conservation equations using Kirchoff’s junction rule.
13. On paper, identify ALL of the possible voltage loops in your circuit. Create the appropriate
potential conservation equations using Kirchoof’s loop rule.
14. Solve for the currents running through, and voltages across, each resistor in your network. Show
your work. At least two members of your team should do these calculations indepdendently.
Label your sketch with the theoretical values for the currents and voltages calculated. These values
represent your hypotheses that are tested in this experiment! Use appropriate significant figures.
QUESTIONS TO ANSWER:
1. Compare the theoretical (hypothetical) value of the current and voltage across each resistor and
power source to the online model and the actual experimental values you obtained.
2. Do your results, taken together, support Kirchoff’s junction and loop rules?
3. Develop explanations for any deviations between experimental and theoretical results.
4. Was there any uncertainty in your results? How precisely can you fairly report your match between
the printed values of the resistors based on their color code bars and your experiment? What could
account for the differences you noted (if any)?
Sample Circuit Sketch and Current Data Table
Currents (Amps)
Theoretical
Online Model
Experimental (+/-)
I1
I2
V1 (theoretical) =
V1 (online) =
V1 (experimental) =
VA (theoretical) =
VA (online) =
VA (experimental) =
VA
I3
V2 (theoretical) =
V2 (online) =
V2 (experimental) =
I1
V3 (theoretical) =
V3 (online) =
V3 (experimental) =
V5 (theoretical) =
V5 (online) =
V5 (experimental) =
I3
I4
I7
I5
I6
I7
VB (theoretical) =
VB (online) =
VB (experimental) =
I2
I6
V4 (theoretical) =
V4 (online) =
V4 (experimental) =
I4
I5
V6 (theoretical) =
V6 (online) =
V6 (experimental) =
VB
I2