Purdue GK-12 Lesson Plan 2006-07
A Solidification of Electricity Concepts through
Laboratory Exploration.
Developed by:
Enrico Manes
Purdue GK-12 Fellow
nino@purdue.edu
Melissa George
Lafayette Tecumseh Junior High Teacher
mgeorge@lsc.k12.in.us
Principal Investigator:
Melissa Dark, Ph.D.
Assistant Dean/ Professor, College of Technology
dark@purdue.edu
Purdue University GK-12 2006-07
This material is based upon work supported by the National Science Foundation under Grant No.
0538643. Any opinions, findings, and conclusions or recommendations expressed in this material are
those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Table of Contents
Unit II: A Solidification of Electricity Concepts Through Laboratory Exploration. ..........................i
1. Overview...................................................................................................................................3
2. Purpose ....................................................................................................................................3
3. Objectives .................................................................................................................................3
4. Indiana Standards Met..............................................................................................................3
4.1. Science ..............................................................................................................................3
4.1.1. Standard 1 - The Nature of Science and Technology..................................................3
4.1.2 Standard 2 - Scientific Thinking ....................................................................................4
4.1.3. Standard 5 - The Mathematical World .........................................................................5
4.1.4. Standard 7 - Common Themes ...................................................................................5
4.2. Math ..................................................................................................................................6
4.2.1. Standard 2 - Computation............................................................................................6
4.2.2. Standard 3 - Algebra and Functions ............................................................................6
4.2.3. Standard 5 - Measurement ..........................................................................................6
4.2.4. Standard 6 - Data Analysis and Probability .................................................................7
4.2.5. Standard 7 - Problem Solving......................................................................................7
5. Methods....................................................................................................................................8
5.1 Materials & Resources ........................................................................................................8
5.2 Procedures..........................................................................................................................8
5.2.1 Preparation ...................................................................................................................8
5.2.2 Background ..................................................................................................................8
5.2.3 Voltage as a Product of Chemistry (2-3 periods) ..........................................................8
5.2.4 Series & Parallel Circuits (4-6 periods).........................................................................8
5.2.5 Resistor Identification and Usage (3-4 periods)............................................................9
5.2.6 Resistors in Practice (2-3 periods)................................................................................9
5.2.7 Ohm’s Law and Kirchhoff’s Law (2 periods) ...............................................................10
5.2.8 Significant Figures through Ohm’s Law and Kirchhoff’s Law (1 period)......................10
5.2.9 Breadboard Introduction (2 periods) ...........................................................................10
5.2.10 Fun with Ohm’s Law and Kirchhoff’s Law (1 period).................................................10
6. Scope ....................................................................................................................................10
7. Activities, worksheets, and Templates...................................................................................10
8. Evaluation..............................................................................................................................10
9. Reflection/Lessons Learned/Alterations for future use ..........................................................11
Resources ..................................................................................................................................11
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1. Overview
This unit covers traditional electricity concepts through the use of current technology in the
hopes of clarifying electrical concepts while targeting a broad base base of learning styles. It is
about 17-22 class periods long if all of the material is used. Many of the units are about 3 day
units and self sufficient. The unit includes both traditional teaching styles along with inquirybased methods. Students learn basic principles of electricity including resistance, energy forms,
electron movement, current, voltage, Ohm’s law, and Kirchhoff’s law.
2. Purpose
The purpose of this lesson is to show students that concepts like resistance, current, and
voltage need not be so abstract; these properties are a result various fields of science and
measurable. These concepts are typically abstract and are quantified by using mathematical
equations like Ohm’s Law and equivalent resistance calculations. The authors wanted to reveal
to the students that the properties lie in the science of the objects being used and that
mathematics can be a tool to help predict results before the measurements. A major
component of the lessons involved measuring electrical properties and comparing those values
to expected values calculated using mathematics. The intent is to,
• reveal the usefulness of mathematics for explaining scientific phenomena,
• reach as many students as possible by approaching electrical concepts from several
angles, and
• provide as many real-world application-based examples as possible.
3. Objectives
The objectives for this project were to:
•
•
•
•
teach the students about the concepts of electricity,
reinforce those concepts through lab measurements,
show the usefulness of mathematics to predict experimental results, and
incorporate measurements in the science classroom.
4. Indiana Standards Met
4.1. Science
4.1.1. Standard 1 - The Nature of Science and Technology
Students design and carry out increasingly sophisticated investigations. They understand the
reason for isolating and controlling variables in an investigation. They realize that scientific
knowledge is subject to change as new evidence arises. They examine issues in the design and
use of technology, including constraints, safeguards, and trade-offs.
Scientific Inquiry
8.1.3
Recognize and describe that if more than one variable changes at the same time in
an experiment, the outcome of the experiment may not be attributable to any one of
the variables.
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4.1.2 Standard 2 - Scientific Thinking
Students use computers to organize and compare information. They perform calculations and
determine the appropriate units for the answers. They weigh the evidence for or against an
argument, as well as the logic of the conclusions.
Computation and Estimation
8.2.2
Determine in what units, such as seconds, meters, grams, etc., an answer should be
expressed based on the units of the inputs to the calculation.
Manipulation and Observation
8.2.3
8.2.4
Use proportional reasoning to solve problems.
Use technological devices, such as calculators and computers, to perform
calculations.
Communication
8.2.7
8.2.8
Participate in group discussions on scientific topics by restating or summarizing
accurately what others have said, asking for clarification or elaboration, and
expressing alternative positions.
Use tables, charts, and graphs in making arguments and claims in, for example, oral
and written presentations about lab or fieldwork.
Matter and Energy*
8.3.8
8.3.9
8.3.10
8.3.13
8.3.15
*
*
*
*
Explain that all matter is made up of atoms* which are far too small to see directly
through an optical microscope. Understand that the atoms of any element* are similar
but are different from atoms of other elements. Further understand that atoms may
stick together in well-defined molecules or may be packed together in large arrays.
Also understand that different arrangements of atoms into groups comprise all
substances.
Demonstrate, using drawings and models, the movement of atoms in a solid*, liquid*,
and gaseous* state. Explain that atoms and molecules are perpetually in motion.
Explain that increased temperature means that atoms have a greater average energy
of motion and that most gases expand when heated.
Explain that energy cannot be created or destroyed but only changed from one form
into another.
Identify different forms of energy that exist in nature.
energy: what is needed to make things move
atom: the smallest particle of an element that has the properties of that element
element: the simplest type of pure substance; a substance consisting entirely of
atoms having identical chemical properties
solid: matter with a definite shape and volume
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*
metals: one class of substances that are mostly shiny, bendable, and good
conductors of heat and electricity
nonmetals: one class of substances that does not have metallic properties; usually a
poor conductor of heat and electricity
heat: a form of energy characterized by random motion at the molecular level
radiation: energy transfer through space
convection: heat transfer in liquids and gases by transport of matter from a region of
one temperature to a region of a different temperature
*
*
*
*
4.1.3. Standard 5 - The Mathematical World
Students apply mathematics in scientific contexts. Students use mathematical ideas, such as
symbols, geometrical relationships, statistical relationships, and the use of key words and rules
in logical reasoning, in the representation and synthesis of data.
Numbers
8.5.1
Understand and explain that a number must be written with an appropriate number of
significant figures (determined by the measurements from which the number is
derived).
Shapes and Symbolic Relationships
8.5.3
Demonstrate that mathematical statements can be used to describe how one quantity
changes when another changes.
Illustrate how graphs can show a variety of possible relationships between two
variables.
Illustrate that it takes two numbers to locate a point on a map or any other twodimensional surface.
8.5.4
8.5.5
4.1.4. Standard 7 - Common Themes
Students analyze the parts and interactions of systems to understand internal and external
relationships. They investigate rates of change, cyclic changes, and changes that
counterbalance one another. They use mental and physical models to reflect upon and interpret
the limitations of such models.
Systems
8.7.1
Explain that a system usually has some properties that are different from those of its
parts but appear because of the interaction of those parts.
Models and Scale
8.7.4
*
Explain that as the complexity of any system increases, gaining an understanding of it
depends on summaries, such as averages and ranges*, and on descriptions of typical
examples of that system.
range: the difference between the largest and the smallest values
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4.2. Math
4.2.1. Standard 2 - Computation
Students compute with rational numbers* expressed in a variety of forms. They solve problems
involving ratios, proportions, and percentages.
8.2.1
8.2.3
Add, subtract, multiply, and divide rational numbers (integers*, fractions, and
terminating decimals) in multi-step problems.
Example: -3.4 + 2.8 × 5.75 = ?, 1 4 5 + - 3 8 × 2 2 = ?, 81.04 ÷ 17.4 – 2.79 = ?.
9
Use estimation techniques to decide whether answers to computations on a calculator
are reasonable.
Example: Your friend uses his calculator to find 15% of $25 and gets $375. Without
solving, explain why you think the answer is wrong.
4.2.2. Standard 3 - Algebra and Functions
Students solve simple linear equations and inequalities. They interpret and evaluate
expressions involving integer* powers. They graph and interpret functions. They understand the
concepts of slope* and rate.
8.3.1
8.3.7
8.3.8
Write and solve linear equations and inequalities in one variable, interpret the solution
or solutions in their context, and verify the reasonableness of the results. Example:
As a salesperson, you are paid $50 per week plus $3 per sale. This week you want
your pay to be least $100. Write an inequality for the number of sales you need to
make, solve it, and check that your answer is reasonable.
Demonstrate an understanding of rate as a measure of one quantity with respect to
another quantity. Example: A car moving at a constant speed travels 90 km in 2
hours, 135 km in 3 hours, 180 km in 4 hours, etc. Draw a graph of distance as a
function of time and find the slope of the graph. Explain what the slope tells you about
the movement of the car.
Demonstrate an understanding of the relationships among tables, equations, verbal
expressions, and graphs of linear functions.
Example: Write an equation that represents the verbal description: “the perimeter of a
square is four times the side length.” Construct a table of values for this relationship
and draw its graph.
4.2.3. Standard 5 - Measurement
Students convert between units of measure and use rates and scale factors to solve problems.
They compute the perimeter, area, and volume of geometric objects. They investigate how
perimeter, area, and volume are affected by changes of scale.
8.5.2
Solve simple problems involving rates and derived measurements for attributes such
as velocity and density. Example: A car travels at 60 mph for 20 minutes. How far
does it travel? What units are appropriate for distance? Explain your answer.
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4.2.4. Standard 6 - Data Analysis and Probability
Students collect, organize, represent, and interpret relationships in data sets that have one or more
variables. They determine probabilities and use them to make predictions about events.
8.6.5
Represent two-variable data with a scatter plot* on the coordinate plane and describe
how the data points are distributed. If the pattern appears to be linear, draw a line that
appears to best fit the data and write the equation of that line.
Example: Survey some of the students at each grade level in your school, asking
them how much time they spend on homework. Plot the grade level and time of each
student as a point (grade, time) on a scatter diagram. Describe and justify any
relationship between grade and time spent on homework.
4.2.5. Standard 7 - Problem Solving
Students use strategies, skills, and concepts in finding and communicating solutions to
problems.
8.7.4
8.7.5
8.7.6
8.7.7
8.7.8
Apply strategies and results from simpler problems to solve more complex problems.
Example: In the first example, write the first five numbers in base 2 notation and look
for a pattern.
Make and test conjectures using inductive reasoning.
Example: In the first example, predict the base 2 notation for six objects, then use
expanded notation to test your prediction.
Express solutions clearly and logically using the appropriate mathematical terms and
notation. Support solutions with evidence in both verbal and symbolic work.
Example: In the first example, explain how you will find the base two notation for
thirteen objects.
Recognize the relative advantages of exact and approximate solutions to problems
and give answers to a specified degree of accuracy.
Example: Measure the length and width of a basketball court. Use the Pythagorean
Theorem to calculate the length of a diagonal. How accurately should you give your
answer?
Select and apply appropriate methods for estimating results of rational-number
computations.
Example: Use a calculator to find the cube of 15. Check your answer by finding the
cubes of 10 and 20.
Students determine when a solution is complete and reasonable and move beyond a particular
problem by generalizing to other situations.
8.7.11
8.7.12
Decide whether a solution is reasonable in the context of the original situation.
Example: In the basketball court example, does the accuracy of your answer depend
on your initial measuring?
Note the method of finding the solution and show a conceptual understanding of the
method by solving similar problems.
Example: In the first example, use your list of base 2 numbers to add numbers in base
2.
Explain exactly how your addition process works.
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5. Methods
5.1 Materials & Resources
The materials required for this activity are:
Calculator
Ruler
Wires
1.5v D size batteries
6v batteries
6v & 12v light bulbs
Light bulb holders
Multi-meters w/test probes
Resistors of varying resistance
Soldering iron and solder
Pencil
Razor blade
Elenco XK-150 (if desired)
80mm x 80mm PC case fan
5.2 Procedures
5.2.1 Preparation
This paper contains several self-contained units and preparation is dependent on which
components are being implemented. If the teacher decides to solder several resistors together
to mimic a 3 position switch then that hardware would need to be prepared in advance.
The teacher will need 6v batteries, wires, and light bulbs in almost all of the units. The
batteries should be tested before use to make sure that they are at 6v.
5.2.2 Background
The primary motivation of the authors was to expose the students to the concepts of
electricity in a lab setting whereby theory is reinforced by laboratory exercises. Concepts such
as current and voltage are abstract concepts at a middle school grade level without the use of
tools to quantify these properties to get a better understanding of what they signify.
5.2.3 Voltage as a Product of Chemistry (2-3 periods)
This unit starts off with the discussion of batteries and how they create free electrons.
The unit starts off with the students enacting the chemical process of a battery and the freeing of
electrons through a group activity. The students are then asked to consider the reasons behind
the choice of metals and their positions on the periodic table. The activity shows the students
where the electrons come from and how they can be made to work for us.
The students then explore what happens when batteries are put together in series. Their
thoughts should be recorded before they begin learning about the functions of the multimeter.
The different DC voltage settings of the multimeter are discussed and the students are then
asked to determine if their original concepts were correct.
This unit was also run in tandem with the typical lemon wet-cell battery.
5.2.4 Series & Parallel Circuits (4-6 periods)
The units in this section expose the students to the concepts of current and voltage
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differences of parallel and series circuits. Circuit symbols are reviewed before delving into the
circuit diagrams.
The flow of electrons are represented by “Elecron-Man” who carries electrons from the
negative side of the battery to the positive side. A definition of a series circuit is given to the
students and they are then asked to determine the series circuit amongst 4 circuit diagrams
before proceeding with the lab. The lab begins with students creating a series circuit using light
bulbs and a 6v battery. They are asked to quantify the brightness of a light bulb and infer
current flow from the brightness of the bulbs along with other characteristics that are unique to
series circuits. A similar approach is provided for a parallel circuit before delving into the
measuring section of the lab.
The students should be encouraged to think about their previous observations while
performing this part of the unit. The idea is to match their ideas from the previous lab with their
measurements from this part of the unit. The students are taught how to make current
measurements using the multimeter and also reminded how to make voltage measurements.
There are drawings and photos to help them through each step of the experiment. At the end of
each section they are asked to summarize what they’ve learned about series and parallel
circuits in one or two sentences. The students should have learned that the current through a
series circuit is the same throughout the circuit and that the voltage drop across each resistor
sums to the battery voltage while the currents through each part of a parallel circuit sum to the
total current leaving and entering the battery and that the voltage across each part of the circuit
is the same as the battery voltage.
5.2.5 Resistor Identification and Usage (3-4 periods)
The students are exposed to the color coding of resistors and using the multimeter to
measure resistance. This allows them to incorporate some simple mathematics and allows the
teacher to incorporate the advantages of the metric system (i.e. 1000 ohms equals 1Kohm).
The students use the tolerance band of the resistors to determine whether the resistor in their
hands meet the manufacturer’s specification. The authors incorporated a discussion involving
the trade-offs between price and low tolerance values from the sides of the manufacturer and
the consumer. The students take this knowledge to the next part of the unit.
The second part of this explores the differences between series and parallel resistors.
The students are asked to predict what the resistance of two resistors in series and two resistors
in parallel are. The instructor may choose this opportunity to discuss the results before
measuring the respective resistances.
5.2.6 Resistors in Practice (2-3 periods)
These activities are the capstone activities of their hard work. The students will use their
knowledge about series and parallel circuits along with series and parallel circuits to predict the
effects of various hardware devices.
The first part of the activity uses 3 or 4 (10 ohm) resistors soldered in series, a couple
wires, light bulb, and a 6v battery so that the students can explore the effects of various contact
positions on the output of the light bulb. This circuit is similar to a household fan with 3 positions
(low, medium, high).
The second part of the activity exposes the students to a potentiometer (variable
resistor). A pencil is sliced down the middle length-wise and the students measure the
resistance at varying increments and plot their results using a best-fit-line approach. They
should observe that the resistance increases as the distance between the probes increase.
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This should be compared to slider dimmer switches and even rotary ones. Voltage to the
controlled device increases as the resistance of the slider decreases. It might be good to point
out that if a 3rd wire was added to the other end of the pencil then as one resistance increases
then the other would decrease and vice-versa. The students then connect the pencil to a circuit
containing a light bulb and can control light intensity.
5.2.7 Ohm’s Law and Kirchhoff’s Law (2 periods)
This lesson can be inserted wherever the teacher sees fit. Some teachers may prefer to
start off with the theory, some might introduce it in the middle of the lessons, and some may
introduce the theory at the end.
The students are exposed to Ohm’s Law and Kirchhoff’s Laws with a formal worksheet to
calculate equivalent resistances.
5.2.8 Significant Figures through Ohm’s Law and Kirchhoff’s Law (1 period)
An exercise and homework are provided for the students to explore significant figures
through the application of Ohm’s Law and Kirchhoff’s Law.
5.2.9 Breadboard Introduction (2 periods)
The breadboard may be an easier device for students to create circuits with and testing
those circuits. An introductory look at a breadboard is provided with a couple exercise so that
the students may become familiar with a breadboard.
5.2.10 Fun with Ohm’s Law and Kirchhoff’s Law (1 period)
The students are asked to vary the rate of revolution of a 12V DC computer fan by
properly choosing the resistance necessary to deliver the desired fan RPM.
6. Scope
The unit can take anywhere from 17-22 class periods depending on the class size and depth of
material coverage. These units are modular and self contained so specific units may be used
without the inclusion of the others.
7. Activities, worksheets, and Templates
Activities, worksheets, and templates are attached at the end of this document.
8. Evaluation
Evaluation sheets are attached with the activities sheets at the end of this document.
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9. Reflection/Lessons Learned/Alterations for future use
Guides for success & Tips:
• Students struggled at first with the understanding of proper multimeter usage and
settings.
• Many students handled the meters by holding their probes which causes the cables to
break requiring dismantling and resoldering of the connections.
• The cost of the meters should not deter a teacher as they can be purchased for well
under $10/pc.
• Breadboards may be introduced earlier than done here as the students quickly
understood how they are used and it may make circuit creation easier. The author
observed several instances where wires were not connected tightly to their contacts
causing the students to second-guess themselves. Using a breadboard should remove
that uncertainty allowing more time to focus on the concepts. Breadboards (without the
Elenco XK-150) were under $5/pc if the proper vendor is chosen.
• Although not shown here, many traditional teaching methods were used in tandem with
the methods shown in this paper to reinforce electrical concepts.
• Much of the hardware was purchased inexpensively at www.omnitron.net or
www.kitsusa.net.
Resources
See pages at the end of this document.
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Electricity Unit
Pre-assessment
Name
1. Please draw 2 batteries in series.
2. Please draw 2 batteries in parallel.
3. What is voltage?
4. What is current?
5. How do you position 2 batteries so that their voltages add (series or parallel)?
6. Assume each battery is 6v. What would the measured voltage be in series and in parallel?
Series voltage:
Parallel voltage:
7. Assume each battery is 6v. What would the measured voltage be in series and in parallel?
Series voltage:
Parallel voltage:
8. Do electrons flow from positive to negative or negative to positive?
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Electricity Unit
Chemistry and Electricity
The authors created an activity to illustrate the chemical reaction that occurs within a battery. This
reaction frees up electrons from both the anode and cathode. It illustrates the requirement of
dissimilar metals in the creation of a battery.
Requirements:
12-24 plastic spheres
student volunteers
Background:
• A student mimics the electrolyte, removing free electrons from the cathode and anode
groups.
• A group of students are assigned to the cathode group and given as many balls (electrons)
as they can hold.
• Another group of students are assigned to the anode group and given as many balls
(electrons) as they can hold.
• The anode group is told that they really want their electrons. This can be demonstrated by
referring to the periodic table of elements.
• The remaining students form a “path” (wire) and pass the free electrons back to the anode.
The process involves having the electrolyte (student) free up the electrons which really want to get
back to the anode but the only way possible is through the “path” which represents the wire from
the cathode to the anode. The students are able to see the flow of electrons and understand that
the process is finite.
Many topics can be discussed such as,
• the reason behind the depletion of batteries
• how electrons flow from the negative side of the battery to the positive
• why the electrons flow from the negative side to the positive side
• temperature dependence since the rate of chemical reactions tend to increase with
temperature. This is also the reason why some manufacturers recommend the storage of
batteries in a cool dry setting.
• shelf life of a battery. Unless the electrons are being used then the battery can hold a
charge for years.
• the use of a switch in a circuit.
• The increase in electron energy through electron liberation and subsequent energy loss as
the electron passes through the circuit to a lower energy level.
• A discussion illustrating a light bulb converting electron energy into light energy through
photons and voltage drop.
• The reason that most batteries tend to be 1.5v cells. This is based on the chemicals used.
This could also cover advanced battery technologies like lithium-ion batteries and the
cost/safety issues of other chemicals. Again, reference to the periodic table is useful in
explaining these concepts.
• 9v batteries as nothing more than (6) 1.5v batteries in series.
• That the (-) terminal is 1.5v higher in potential than the (+) end but even if the potential
difference was 0V that it could still have a potential difference when compared to ground
which can be measured using the multi-meters.
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Electricity Unit
The electrolyte (usually a liquid or paste) in the battery removes electrons from both electrodes
(usually a metal). They are designed so that one electrode gives more electrons than the other
and so has a lot of electrons near it which gives it a negative charge. That electrode is usually
called the cathode. The other electrode also loses electrons and becomes positive but it wants
those electrons more than the cathode; that electrode is called the anode. In a battery, the
electrons flow from the cathode to the anode.
A chemical reaction is what causes the electrons to be removed from their metals. Energy
must be added to remove the electron so that it can escape the base metal. This causes the
electron to have more energy than its restful state. This added energy is what causes a battery to
have a voltage. Once the chemical reaction stops and all of the electrons return to their restful
state the battery will have 0 volts of difference between both ends.
If we are looking at a 1.5V battery then the electrons at the negative terminal have 1.5V of
more potential energy than the positive terminal.
The chemical reaction caused
the electrons to gain energy
when compared to the (+)
terminal.
--------
The (-) end has 1.5V
more potential than
the (+) end
So what would happen when we put one battery on top of the other? Remember that the (-)
terminal is 1.5V greater than the (+) end.
The (-) end of battery (1) has 1.5V
more potential than the (+) end of
battery (1)
The (-) end of battery (2) has 1.5V
more potential than the (+) end of
battery (2)
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--------
How much more potential does the (-)
terminal of battery 2 have over the (+)
terminal of battery (1)?
2
--------
14
Electricity Unit
Using the Multi-Meter to Measure Voltage
A multi-meter is a tool that can measure many different types of electricity related properties
(hence the name). The meter you are using is shown below.
Multi-Meter Handling Tips:
Please don't hold the meter or move the meter by dangling the meter by the test
probes. This WILL cause the wires to break inside the probes.
Please turn the dial slowly. Quickly turning the dial will result in damage to the
pieces inside.
Today we'll be measuring DC voltage. One needs to be careful to use the meter properly
otherwise damage can occur to the meter or the user. When measuring DC voltage the dial needs
to be in the DCV area circled below. The meters need to be set to the proper range to work
properly.
DCV Setting
Value
Meaning
1000
The meter can measure between 200V and 1000V
200
The meter can measure between 20V and 200V
20
The meter can measure between 2000milli-Volts and 20 V
2000m
The meter can measure between 200milli-Volts and 2000 milli-volts
200m
The meter can measure between 0V and 200milli-volts
You'll be measuring voltages under 20V but more than 2000milli-volts so set the meter to 20.
Connect the red probe to the (V-W- mA) port and the ground to COM port as shown below. This is
the proper
setting to measure Voltages,
Resistances,
and small (milli) Current.
--------
Measure the voltage of Battery 1 and record here:
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Electricity Unit
In the next series we will measure the voltages of the individual batteries in series and then
the total voltage of the stack when they are put in series.
Step1: Measure the voltage of Battery 1 and record below
1
2-------
2
2
--------
Step3: Connect the (+) of Battery 2 to
the (-) of Battery 1 to create a Battery
1/Battery 2 pair and record the voltage
below.
Step2: Measure the voltage of Battery 2 and record below,
Step 1 (Battery 1 voltage):
Step 2 (Battery 2 voltage):
Step 3 (Battery 1/Battery 2 pair voltage):
Perform the following arithmetic:
Battery 1 voltage + Battery 2 voltage =
Compare this voltage with what you measured in step 3 and discuss:
Various Circuit Symbols
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Electricity Unit
What we see
How it is represented
batteries
Wires
Resistors, light bulb, heater,
radio, anything that uses
electricity
Capacitors
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Electricity Unit
Series Discussion
In sports series like The World Series the team must play one game at a time. In track a runner
needs to run over a series of hurdles, one hurdle at a time. In electricity, we use the same
terminology for a circuit where the electron must run through one object before it can go to the next
one.
In the figure below, Electron-Man is carrying an electron from the negative terminal of the battery to
the positive terminal of the battery. To get there, he must run through obstacle 1 and after
completing obstacle one he enters obstacle 2. This would be considered a series circuit because
the electron cannot run through obstacle 2 without going through obstacle 1. The flow of electrons
(current) MUST go through 1 before getting to 2 and finally arriving at the battery, 3.
2
3
1
This can be drawn in many different ways but the ONLY question that you need to ask yourself is,
“Can the electron get the (+) terminal without going through every obstacle?”
If the answer is no, then you've identified a series circuit.
Q1: Identify the series circuits below,
It usually helps to draw the electron flow(s) using arrows to show the different paths.
2
I
II
1
2
1
2
III
1
2
IV
1
Q2: Is there a difference to Electron-Man between circuits I, II, III, and IV? If not, which ones are
the same.
If so, which ones are different and why?
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18
Electricity Unit
Series Circuit - LAB
Group Names
I. Series Circuit Setup
Find a way to set up a series circuit using 4 alligator clips, the circuit board,
and a battery. Make sure that all three resistors are part of your circuit.
Draw a circuit diagram for your circuit using the correct symbols.
Have Mrs. George okay your circuit before moving on.___
II. Connect the circuit and write down what happens. Give each bulb a
brightness rating (from 1-10).
III. Now, unscrew one of the light bulbs. Give each bulb in the circuit a
brightness rating. What happens? Why do you think this happens?
IV. Now exclude one light bulb from the circuit and reconnect the circuit. Give
each bulb in the circuit a brightness rating. What happens? Why do you
think this happens?
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19
Electricity Unit
V. Now exclude another light bulb from the circuit and reconnect the circuit.
Give each bulb in the circuit a brightness rating. What happens? Why do you
think this happens?
VI. Now try to create a short circuit. A short circuit is an unintended path that
usually bypasses resistors. Draw your short circuit using a circuit diagram
Explain what happens when you create your short circuit.
VII.
Summarize your observations about series by listing 3 patterns that you
noticed.
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20
Electricity Unit
Parallel Discussion
In math, a set of parallel lines contains two lines that are running side-by-side. In gymnastics, the
parallel bars are two bars that run along each other but at different heights. Some streets run
parallel to each other and cars park parallel to each other in a parking lot. In electricity, we use the
same word to describe when an electron can flow through one obstacle without being forced to run
through another one.
In the figure below, Electron-Man is carrying an electron from the negative terminal of the battery to
the positive terminal of the battery. To get there, he can run through obstacle 1 or obstacle 2 to
get to the (+) battery terminal. This would be considered a parallel circuit because the electron
isn't forced to run through one obstacle to get to the other. The flow of electrons can go through
EITHER 1 or 2 before finally arriving at the battery, 3.
3
2
1
This can be drawn in many different ways but the ONLY question that you need to ask yourself is,
“Can the electron get the (+) terminal without going through every obstacle?” If the answer is yes,
then you've identified a parallel circuit.
Q1: Identify the series circuits below,
It usually helps to draw the electron flow(s) using arrows to show the different paths.
I
1
II
2
2
1
III
1
2
1
2
IV
Q2: Is there a difference to Electron-Man between circuits I, II, III, and IV? If not, which ones are
the same.
If so, which ones are different and why?
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21
Electricity Unit
Series & Parallel Circuit Extra Credit
Identify which parts of the following circuit is in series and which parts are in parallel. You can
discuss obstacles as groups if it helps you discuss them but you don't have to.
6
5
3
4
2
1
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22
Electricity Unit
Parallel Circuit - LAB
Group Names
I. Parallel Circuit Setup
Find a way to set up a parallel circuit using 6 alligator clips, the circuit
board, and a battery. Make sure that all three resistors are part of your
circuit. Draw a circuit diagram for your circuit using the correct symbols.
Have Ms. George okay your circuit before moving on.___
II. Connect the circuit and write down what happens. Give each bulb a
brightness rating (from 1-10).
III. Now, unscrew one of the light bulbs. Give each bulb in the circuit a
brightness rating. What happens? Why do you think this happens?
IV. Now exclude one light bulb from the circuit and reconnect the circuit. Give
each bulb in the circuit a brightness rating. What happens? Why do you
think this happens?
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23
Electricity Unit
V. Now exclude another light bulb from the circuit and reconnect the circuit.
Give each bulb in the circuit a brightness rating. What happens? Why do you
think this happens?
VI. Now brainstorm some ways you might like to reconnect the circuit. Pick one
of these ways and draw a circuit diagram below first.
Make a prediction about what will happen when you hook it up.
Why do you think this will happen?
Now hook it up, what happens?
VII.
Summarize your observations about parallel by listing 3 patterns that
you noticed.
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24
Electricity Unit
Current and Voltage Unit – Series Circuits
As you've seen, Electron-Man carries the electrons from the (-) terminal to the (+) terminal of the
battery. The speed at which the electrons move is called current.
What do you think: Is the flow of electrons (current) different through obstacle 1 than through
obstacle 2?
2
3
1
Do we have a way of finding out? YES, the multi-meter!
Measuring Current with the Multimeter:
One of the electrical measurements that the multi-meter can make is current. The way we do this
is by using the multi-meter as part of the circuit which is different than when we measure voltage.
Plug the red probe into the 10A setting on the multi-meter (MM). It is located right above the
(V-W- mA) port
Set the multimeter to the 10A setting to measure currents up to 10A. Hopefully we'll be well
below that.
2
Step 1: Measure the current to the first light bulb.
3
1
Record your measurement:
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25
Electricity Unit
Step 2: Measure the current between bulb 1 and bulb 2.
2
3
1
Record your current measurement:
Step 3: Measure the current between bulb 2 and (+) terminal.
Record your current measurement:
2
3
1
So, what have you learned? Is the current different at different parts of the circuit? Can you make
a statement about current and series circuits? Write a few sentences explaining your
observations.
Connect the circuit so that both light bulbs are on without using the meter. Now take one light bulb
out. What happens? Can you explain?
Make a statement about current and series circuits, something that HAS to be true.
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26
Electricity Unit
Now we're going to explore how the voltage changes as the current flows through the circuit. You'll
need to set the MM back to the voltage setting (20 DCV) and put the red probe wire back on the
(V-W- mA) port. Note that when we measure voltage we don't actually have to create breaks in the
circuit like we did when we measured current.
Step 1: Measure the battery voltage in the circuit and record here:
2
3
1
2
Step 2: Measure the voltage across the first
light bulb in the circuit and record here:
3
1
Step 3: Measure the voltage across the second
light bulb in the circuit and record here:
2
3
1
Add the voltages measured at 1 (Step 2) and 2 (Step 3) and compare to the voltage at 3 (Step1).
Do you notice anything? Can you explain what is happening in terms of the potential energy of the
battery? Write a few sentences explaining what you observed and what you think is happening
How bright are the light bulbs? Can you explain your observation based on the measured
voltages?
Make a statement about voltages for series circuits, something that HAS to be true?
Team Tecumseh - Hands on Electricity Exploration
27
Electricity Unit
Current and Voltage Unit – Parallel Circuits
As you've seen, Electron-Man carries the electrons from the (-) terminal to the (+) terminal of the
battery. The speed at which the electrons move is called current.
What do you think:
Is the flow of electrons (current) different through obstacle 1 than through obstacle 2?
Is the flow of electrons going into 1 & 2 (big Electron-Man) different than that going through
1 or 2
(smaller Electron-Men)
3
1
2
-
Do we have a way of finding out?
YES, the multi-meter! One of the electrical measurements that the multi-meter can make is
current. The way we do this is by using the multi-meter as part of the circuit which is different than
when we measure voltage.
Plug the red probe into the 10A setting on the multi-meter (MM). It is located right above the
(V-W- mA) port
Set the multimeter to the 10A setting to measure currents up to 10A. Hopefully we'll be well
below that.
Step 1: Measure the current to the first light bulb.
3
2
1
Record your measurement:
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28
Electricity Unit
Step 2: Measure the current between the battery and bulb 2.
Record your current measurement:
2
3
1
Step 3: Measure the current between the (-) terminal and BOTH bulbs. This is the current
going INTO the circuit.
Record your current measurement:
3
2
1
Step 4: Measure the current between the (+) terminal and BOTH bulbs. This is the current
coming OUT of the circuit.
3
2
1
So, what have you learned? Is the current different at different parts of the circuit? Can you make
a statement about current and parallel circuits? Write a few sentences explaining your
observations.
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29
Electricity Unit
Connect the circuit so that both light bulbs are on without using the meter. Now take one light bulb
out. What happens? Can you explain?
Are Christmas Tree lights connected in series or parallel, why?
What did you notice about the currents going into and coming out of the circuit?
Add up the currents going through light bulb 1 and light bulb 2 Now compare that current to the current coming into and out of the circuit. Make a statement
about your observations.
Make a statement regarding current and parallel circuits, something that HAS to be true.
Team Tecumseh - Hands on Electricity Exploration
30
Electricity Unit
Now we're going to explore how the voltage changes as the current flows through the circuit. You'll
need to set the MM back to the voltage setting (20 DCV) and put the red probe wire back on the
(V-W- mA) port. Note that when we measure voltage we don't actually have to create breaks in the
circuit like we did when we measured current.
Step 1: Measure the battery voltage in the circuit and record here:
3
2
1
Step 2: Measure the voltage across the second light bulb in the circuit and record
here:
3
2
1
Step 3: Measure the voltage across the first light bulb in the circuit and record here:
3
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2
1
31
Electricity Unit
Compare the voltages measured at positions 1, 2, and 3. What have you learned?
Do you notice anything? Can you explain what is happening in terms of the potential energy of the
battery? Write a few sentences explaining what you observed and what you think is happening
How bright are the light bulbs? Can you explain your observation based on the measured
voltages?
Make a statement about voltage and parallel circuits, something that HAS to be true.
Extra Credit
Consider a pair of light bulbs in series compared to a set of light bulbs in parallel. Which would be
dimmer? Propose an idea or method to make them brighter using batteries, wires, or light bulbs.
You cannot change the configuration of the dimmer light bulb set; this means that if you chose
parallel as the dimmer set then the light bulbs must remain in parallel and if you chose series as
the dimmer set then the light bulbs must remain in series.
Feel free to draw a sketch below,
Team Tecumseh - Hands on Electricity Exploration
32
Electricity Unit
Post-assessment
Name:
1. Please draw 2 batteries in series.
2. Please draw 2 batteries in parallel.
3. Please draw 2 light bulbs in series.
4. Please draw 2 light bulbs in parallel.
5. Will the voltage of 2 batteries be greater when in series or in parallel? Why?
6. Assume each battery is 6v. What would the measured voltage be in series and in parallel?
Series voltage:
Parallel voltage:
7. Would light bulbs connected in series or parallel be brighter?
8. Will the current of 2 batteries be greater in series or in parallel? Why?
9. Assume each battery can provide 2A (amps) of current to a light bulb circuit. What would
the measured current be in series and in parallel?
Series voltage:
Parallel voltage:
10. Do electrons flow from positive to negative or negative to positive?
11. Explain what happens when you put 2 batteries in series in terms of voltage and current.
Current:
Voltage:
Team Tecumseh - Hands on Electricity Exploration
33
Electricity Unit
12. Explain what happens when you put 2 batteries in parallel in terms of voltage and current.
Current:
Voltage:
13. Explain what happens when you put 2 light bulbs in series in terms of voltage and current.
Current:
Voltage:
14. Explain what happens when you put 2 light bulbs in parallel in terms of voltage and current.
Current:
Voltage:
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34
Electricity Unit
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35
Electricity Unit
Team Tecumseh - Hands on Electricity Exploration
Tolerance
%
Tolerance
%
________
________
________
________
________
________
________
________
________
________
36
Electricity Unit
Tolerances
Like most things in life, nothing is perfect. When manufacturers create resistors it is close to
impossible for them to make each resistor perfectly equal the number indicated by the colored
bands on their exterior. They try to make the resistors equal to the resistance that they are after
but they don't always get it perfect so they leave themselves with a window of error and let the
customer know that the resistor will be in that windows.
They accomplish this by using a tolerance window. For example, I might tell someone that I'm 6
feet tall +/- 1/2” which means that I'm pretty sure I'm somewhere between 5'-11.5” and 6'-0.5”.
Fun fact : Did you know that a person's height changes throughout the day? A person is usually
taller in the morning than at night because they've had gravity pulling down on them all day and the
tissues in the spine compress under the person's weight.
Using a tolerance of +/- 1/2” is more accurate than saying 6' because a person's height changes.
This is the reason that we use tolerances in the scientific community.
Here's how they use tolerances with resistors,
A sample resistor has the color bands red, blue, green, red and gold.
What is that resistor's value?
What is the resistor's tolerance %?
If the resistors band is gold then there is a 5% tolerance which means that you must multiply 5%
(0.05) times the value of the resistor to figure out what the tolerance is in ohms.
For example, if my resistor was 100 Ohms and had a tolerance value of 5% then my tolerance
would be
0.05 x 100 ohms = 5 ohms
this means that the tolerance is +/- 5 ohms and if that resistor was measured then the
resistance should be 100 ohms +/- 5 omhs or,
100 ohms + 5 ohms = 105 ohms
100 ohms – 5 ohms = 95 ohms
For the resistor to be made within the manufacturer's specification then the resistor needs to have
a resistance value between 95 ohms and 105 ohms. So long as the resistor is within this range
then the manufacturer can sell it as a 100 ohm resistor with a 5% tolerance band.
Questions:
Why do you think there are 3 different tolerance levels (2%, 5%, and 10%)?
Which do you think would be more expensive to make?
Which do you think would cost more?
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37
Electricity Unit
Tolerance Worksheet
Note: that some resistors are 4-band and some are 5-band
Resistor Colors Resistor Value Tolerance % Tolerance Value
Range of
(Ohms)
(Ohms)
acceptable
(based on colors)
+/resistor values
(Ohms)
Measured
resistance
values
(Ohms)
Put a check if
ok
Brown black
brown silver
Yellow violet
red silver
Red red red
silver
Orange orange
brown red
Brown black
red silver
Yellow violet
orange silver
Yellow violet
yellow silver
Red red brown
gold
Brown green
brown gold
Brown black
yellow silver
Yellow violet
brown silver
Team Tecumseh - Hands on Electricity Exploration
38
Electricity Unit
Resistor Quiz
Use the following color tables to help you correctly identify the 4-band and 5 band resistors below.
The last column is the Multimeter setting column. Tell us where you would turn the dial on the
multimeter to measure that resistor.
Resistor Value
(don't forget
units)
Range of
Tolerance Toleranc
%
e
acceptable
Value
resistor values
+/(don't forget units)
Multimeter
setting
red
brown
brown
silver
Resistor
brown
black
red
orange
brown
1
orange
yellow
white
blue
2
orange
violet
black
brown
3
brown
orange
red
black
brown
4
5
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39
Electricity Unit
Parallel/Series Resistors
Today you are going to learn what happens to the resistors when you put them together in series
and parallel.
Let's assume you have 2 resistors each with a resistance of 150 ohms.
Predict what the resistance would be of the two resistors when in series.
Measure the resistances of each resistor and record,
Resistor 1:
1
2
Resistor 2:
The resistors in series:
Recall that V=IR. Imagine that these resistors were
part of a series circuit connected to a 6v battery.
How does the current change as the more resistors are
added in series?
Predict what the resistance would be of the two resistors when in parallel.
Resistor 1 (from above):
Resistor 2 (from above):
The resistors in parallel:
Recall that V=IR. Imagine that these resistors were part of a
series circuit connected to a 6v battery.
How does the current change as more resistors are added in parallel ?
See if you can come up with an equation that explains what happens when you put 2 resistors in
series and another formula that explains what happens when you put 2 resistors in parallel.
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40
Electricity Unit
Parallel/Series Resistors Quiz
brown
violet
green
black
gold
1. Find the resistance of the resistor below.
2. What is the tolerance and range of this resistor?
3. If two of these resistors were strung together in series, what would you expect the
resistance to be?
4. To test these resistors, what setting would you use on the multimeter?
5. If two of these resistors were strung in parallel, what would you expect the resistance to be?
6. To test these resistors, what setting would you use on the multimeter?
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41
Electricity Unit
Resistors in Series Lab
You've been given a set of resistors that are soldered (like glue) together.
Are all the resistors the same resistance?
How did you check?
Examine the circuit below before connecting the wires to it and predict how moving the end of the
black wire from point 1 to point 2 and so on until point 4 will affect the brightness of the light bulb.
4
3
2
1
Touch the bottom of the bulb to the top of the battery
and one end of the red wire to the side of the bulb.
Move the black wire to each of the bare spots in the row of resistors starting at spot 1 and going to
spot 4. Explain what is going on with the light bulb.
Try to explain why you think that this is happening.
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42
Electricity Unit
Potentiometers – A Whole Bunch of Little Resistors in Series
Below is a figure of a pencil cut in ½ along its length, exposing the graphite lead. Graphite is a
conductor and today we'll explore what happens when resistances are measured at different
places along that conductor.
Below you will find different locations to measure the resistance as you keep one of the probes
fixed and move the other. Record all resistances in table below and the distances to where you
measured.
Total
resistance
How do you think the resistance will change as you move the read probe? Will the resistance in
the middle of the pencil be 1/4 of the total, ½ of the total, ¾ of the total, the same as the total, or 2x
the total resistance?
Let's find out!
Record all your measured resistances and the spots at which you measured the resistances with a
ruler, setting the 0 of the ruler at the left end.
0”
1”
Distance
2”
3”
4”
Measured Resistance
(ohms)
5”
6”
7”
Brightness of Bulb (see below)
0”
1”
2”
3”
4”
5”
6”
7”
(enter full length of pencil)
Explain your observations?
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43
Electricity Unit
Potentiometers
Below you will find different locations to examine the brightness of a bulb connected as shown
below.
Touch the bottom of the bulb to the top of the battery,
one end of the red wire to the side of the bulb, and slide
the black wire along the graphite.
Fill in the table on the previous page with your brightness on a scale from 1-8.
What do you think is going on?
The drawing below would be a circuit diagram for what you have created above.
Variable resistor
(potentiometer)
Here's your chance to impress Mr. Manes.
Can you explain in terms of voltage what is going?
Hints: Ohm's Law and how current flows through a series circuit. Think about your previous
experiments that might be similar to this one.
Feel free to use the multi-meter to figure it out.
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44
Electricity Unit
Potentiometers - Graph
Graph the resistance versus distance and feel free to use Excel and tell us what the resistance per inch of graphite it.
How long of a piece of graphite would I need for a 200 ohm resistor? Is the graphite of a pencil a good material to use
for a resistor?
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45
Electricity Unit
Potentiometers – Creative Fun Homework, Extra Credit
Let's examine what you've learned so far. You've learned,
how sliding potentiometers work
how to measure resistance, current, and voltage with a multi-meter
how to read a circuit diagram
how current flows through a series circuit and a parallel circuit
Based on what you know, I'd like to see you draw a circuit diagram to improve upon the sliding
potentiometer above. The problem with building a potentiometer like the one above is that the wire
moves. Moving a wire back and forth is like bending a paperclip back and forth, eventually it will
break. Can you come up with a drawing showing how you might build a sliding potentiometer
where the wires don't move?
You are free to add extra parts and draw anything that you can think of to make it work so long as
the current flows properly throughout your entire circuit.
EXTRA-EXTRA-CREDIT
Can you draw a diagram for how to convert a potentiometer that slides back and forth into one that
turns like a knob on a radio or a household light dimmer?
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46
Electricity Unit
Elenco XK-150
Dear parents of children in my science classroom,
Your son or daughter will soon be exposed to an expensive piece of hardware that was purchased
through a National Science Foundation grant for use in science exploration with my Purdue GK12
fellow. The Elenco XK-150 is a sensitive piece of equipment that can perform a multitude of
functions, some of which include,
Variable DC power supply
AC power supply
Function generator
Potentiometers
Digital logic functions
We'd like you to speak to your son or daughter about how fortunate they are to have access to
these tools within their classroom in hopes of preventing any misuse of the equipment in the
coming weeks. I've added a photo of the device just in case you were wondering what the
hardware looked like.
I ________________________(parent) ____________(date) have spoken to my son or daughter
and we have discussed the importance of using this hardware appropriately.
I _________________________(student) __________(date) understand that I will not misuse the
equipment given to me in science class and will be held responsible for any misuse that causes
damages.
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47
Electricity Unit
Elenco XK-150
Today you'll be getting introduced to new equipment that has many separate functions built into 1
tool. Below is a table highlighting some of the parts that you've been exposed to and their
replacement on the XK-150.
Previous Parts
Elenco XK-150
Battery
Variable power supply
Light bulbs
Resistors
Electrical boards
Breadboard
Before we proceed we need to know that the equipment will be handled responsibly. You are one
of very few students in the country that have equipment like this and it is very expensive so if
anything is broken from horsing around you will be held responsible.
I,____________________, ______________________, _______________________,
_____________________, _______________________, ______________________, realize that
this is very sensitive equipment and I am financially responsible if the equipment is broken while in
my possession.
A photo of the XK-150 is shown below with parts highlighted,
Variable
Power
Supply
Variable
Resistor
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Breadboard
48
Electricity Unit
Elenco XK-150 – Breadboard
The breadboard is supposed to be a neat area where you can try some different things with your
circuits. These boards are used quite a bit in college in electrical engineering courses. Do you
remember the series resistors that were soldered together? The breadboard allows you to create
a circuit without soldering.
There are 2 halves to the breadboard and no part of half 1 is connected to half 2. Every hole in the
power row is connected to every other hole in that row.
Each hole in the row is
connected to the other holes in
the row.
Each hole in the row is
connected to the other holes in
the row.
Each column of 5 holes are
connected together but not
connected to any other
columns.
Half 1
Half 2
Use your multi-meters and wires (with straight ends) to prove these features to yourself.
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49
Electricity Unit
Ohm's Law & Kirchhoff’s Law
Today we are going to explore what happens when you put resistors in series and in parallel using
the breadboard. Some of this should be easy for you by now.
Are the resistors in Half 1 below in series or parallel? Explain in terms of the connections of the
breadboard and how current would flow. Feel free to draw arrows showing how the current would
flow.
Are the resistors in Half 2 below in series or parallel? Explain in terms of the connections of the
breadboard and how current would flow. Feel free to draw arrows showing how the current would
flow
Resistance
Measureme
Resistance
Measureme
Add another resistor to the circuit that you think is series and record the measured resistance.
Explain your observations.
Add another resistor to the circuit that you think is parallel and record the measured resistance.
Explain your observations.
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50
Electricity Unit
Ohm's Law & Kirchhoff’s Law
For the past several weeks you've explored what happens when you put resistors in series and
parallel. You've explored what happens to the voltages and currents.
These properties were discovered by scientists called Ohm and Kirchhoff and they have very
important laws attributed to them.
Ohm's Law:
V = IR
Kirchhoff’s Laws:
Current Law – The sum of the currents going into a connection must equal the sum of the
currents leaving the connection.
i2
i1 = i2 + i3
i1
I3
Voltage Law – The sum of the voltages around a circuit must be equal to zero.
Using Kirchhoff’s Laws and Ohm's Law and lots of algebra you would learn that for resistors in,
Series: The total resistance of resistors in series is the sum of the resistors.
Requivalent = R1 + R2
R2
R1
Parallel: You can add the resistors in a series to get the total resistance.
1
R1
R2
R equivalent
=
1
R1
1
R2
R equivalent =
R1 R2
R1 R2
Now use this information to answer the questions on the previous page!
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51
Electricity Unit
Ohm's Law & Kirchhoff’s Law - Homework
4W
2W
6W
4W
2W
4W
4W
4W
4W
4W
2W
4W
10 W
4W
Do the following for homework and be sure to show your work,
1W
10 W
5W
2W
3W
What would be the current going into the circuit above if there was a 12V battery connected it?
Can you draw the flow of current(s) through the various parts using arrows?
4W
10 W
4W
4W
What would be the current going into the circuit above if there was a 12V battery connected it?
Can you draw the flow of current(s) through the various parts using arrows?
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52
Electricity Unit
Ohm's Law & Kirchhoff’s Law – Let's Have Fun
Let's take what we've learned and get creative!
Remember that everything in a circuit has some resistance; even the wires have resistance.
The light bulb has a resistance of 2 ohms. Let's assume that the graphite has a resistance of 15
ohms.
What is the current through the circuit?
What is the voltage loss at the light bulb?
What is the voltage loss at the graphite?
Light bulb
2 ohms
6 volts
15 ohms
Let's assume that the graphite has a resistance of 30 ohms.
What is the current through the circuit?
What is the voltage loss at the light bulb?
What is the voltage loss at the graphite?
Light bulb
2 ohms
6 volts
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30 ohms
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Electricity Unit
Ohm's Law & Kirchhoff’s Law – Significant Figures
Today we'll learn about how to calculate significant figures when reporting scientific data.
Significant Figures:
In short, you can't be more sure of your results than with the numbers that you started with.
What does this mean?
Whenever a measurement is taken there is some accuracy associated with it. If someone
hands you a 6 v battery and the voltage is measured with a multi-meter to show that the voltage is
5.5 volts. We couldn't say that we know the voltage to the hundredths decimal place (i.e. 5.5x)
place. So we only have 2 significant figures in our original voltage measurement and therefore any
numbers that are generated using 5.5 volts can't have anymore than 2 decimal places of accuracy.
The answer cannot have anymore significant figures than the least accurate measurement.
What about zeros?
If the zero is used as a place holder then it typically not a significant figure. For example,
100 has 1 significant figure, 101 has 3 significant figures (if the zero is between 2 non-zero
numbers then the zero is significant. One of the easiest ways to determining whether the number
is significant is to write it in scientific notation, meaning
100 = 1 x102 - it’s easier to see the 1 significant figure
101 = 1.01 x102 – it’s easier to see that there are 3 significant figures
What about when the zero is behind the decimal place? 0.05 only has 1 significant figure
because it can be rewritten as 5 x10-2.. This clearly shows that there is only 1 significant figure.
What about 10.05? Since the zeros are between 2 nonzero numbers (1 & 5) then they are
significant so 10.05 has 4 significant figures.
Let's do some examples!
We all know that V=IR so let's use Ohm's law as the equation for our examples.
Example 1 : Find the current if the voltage is 5.5 volts and the resistance is 35 ohms.
I= V/R so I= 5.5/35 = 0.157142857143
In this case the 5.5 has 2 significant figures and the 35 has 2 significant
figures so the answer cannot have more than 2 significant figures. Therefore the answer can only
have 2 significant figures.
I=0.16 (it's ok to round up or down)
In simple terms, it would be inaccurate to say that the current was known to more than 2 decimal
places because we would need a more accurate voltage and resistor measurement to be able to
say that is true.
Let's do another,
Example 2 : Find the current if the voltage is 5.5 volts and the resistance is 8 ohms.
I= V/R so I= 5.5/8= 0.6875
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54
Electricity Unit
In this case the 5.5 has 2 significant figures and the 8 has 1 significant figure so the answer cannot
have more than 1 significant figure. Therefore the answer can only have 1 significant figure.
I=0.7 (it's ok to round up or down)
Let's do another,
Example 3 : Find the current if the voltage is 6 volts and the resistance is 13 ohms.
I= V/R so I= 6/13= 0.46153
In this case the 6 has 1 significant figure and the 13 has 2 significant figures
so the answer cannot have more than 1 significant figure. Therefore the answer can only have 1
significant figure.
I=0.5 (it's ok to round up or down)
Do the following for homework,
Problem 1: V=6 volts and I = 100 amperes. Find the resistance and don't forget the units.
Problem 1: V=6.6 volts and I = 100 amperes. Find the resistance and don't forget the units.
Problem 1: V=6.67 volts and I = 100 amperes. Find the resistance and don't forget the units.
Problem 1: V=6.0 volts and I = 100 amperes. Find the resistance and don't forget the units.
Problem 1: V=6.00 volts and I = 100 amperes. Find the resistance and don't forget the units.
Problem 1: V=6 volts and I = 110 amperes. Find the resistance and don't forget the units.
Problem 1: V=6.6 volts and I = 111 amperes. Find the resistance and don't forget the units.
Problem 1: V=6.67 volts and I = 100.0 amperes. Find the resistance and don't forget the units.
Problem 1: V=6.0 volts and I = 100 amperes. Find the resistance and don't forget the units.
Problem 1: V=6.00 volts and I = 100 amperes. Find the resistance and don't forget the units.
Problem 1: V=6.670 volts and I = 100.0 amperes. Find the resistance and don't forget the units.
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55
Electricity Unit
Ohm's Law & Kirchhoff’s Law – Let's Have Fun
Let's take what we've learned and get creative!
Remember that everything in a circuit has some resistance; even the wires have resistance.
Can you choose the resistors required to reduce the voltage from 12 volts so that 2 resistors in the
circuit both have 6 volts?
? ohms
12 volts
1
2
? ohms
Let's make the experiment more real-world. You have a 12V fan that has a resistance of 100
ohms and spins at 2500 rpm when given 12 volts as shown in the graph below. Can you put the
proper resistor in spot 1 so that it spins at 1250 rpm?
Hint: What voltage does the fan need to spin at 1250 rpm and how can you make sure that it gets that voltage?
12V DC Fan Profile
12
Voltage to Fan (voltage)
11
10
9
8
7
6
5
4
3
2
1
0
0
250
500
750
1000
1250
1500
1750
2000
2250
2500
Fan Speed (RPMs)
What happens if the resistor in spot 1 increases? Does the fan spin faster or slower?
Try it!
Extra Credit Question:
If you were the manufacturer of an iPod that required 4 volts and had a resistance of 10K-ohm and
the battery was 6v then how would you make sure that the iPod only received 4 volts?
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56
Electricity Unit
Elenco XK-150 – Power Supply
Connect the MM as shown below and turn the LEFT knob of the variable power supply. Make sure
that the probe tips are touching the metal inside the colored thumb screws.
Record your observations in the table below.
Turn the RIGHT knob and record your observations in the table below.
1
2
3
Now connect the red probe to the yellow plug and turn the RIGHT knob.
Record your observations in the table below.
Turn the LEFT knob and record your observations in the table below.
MM Connection
Adjusting the left knob
observations
Adjusting the right knob
observations
Max Voltage:
Min Voltage:
Max Voltage:
Min Voltage:
Max Voltage:
Min Voltage:
Max Voltage:
Min Voltage:
Red probe on 1
Black probe on 2
Red probe on 3
Black probe on 2
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Electricity Unit
Elenco XK-150 – Power Supply
As you've learned all circuits need a + terminal and a – terminal so you only have 2 wires but you
have 3 terminals of the variable power supply. We need your help because we have 3
experiments to run and need to figure out how to connect the 2 power wires. Please help us
connect the wires to the proper terminal for,
Experiment
Number
Connect the red wire to which
terminal
Connect the black wire to which
terminal
1 – 0 to 15 volts
Red, black, or yellow
Red, black, or yellow
2 – 0 to – 15 volts
Red, black, or yellow
Red, black, or yellow
3 – 0 to 30 volts
Red, black, or yellow
Red, black, or yellow
Ask your teacher for to come by and check off your answer before proceeding _______(teacher
initials)
Now use the MMs to check your answers!
There is more than 1 way to connect the wires for each experiment. Can you think of some other
ways?
Ask your teacher for to come by and check off your answer before proceeding _______(teacher
initials)
Now use the MMs to check your answers!
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Electricity Unit
Elenco XK-150 – Variable Resistor
You've learned that resistors can come in different resistances but what if you could buy 1 resistor
that could actually be any resistance that you wanted, within reason of course.
Set the MM to the 2000W setting and connect the red probe to the hole labeled 1 below and the
black probe to the hole labeled 3 below.
Record your reading __________.
Turn the 1k Ohm knob and explain what you see happening____________________________.
Connect the red probe to 1 and the black probe to 2 and record your reading
________________________.
Turn the 1k Ohm knob and explain what you see happening
________________________________
Turn the knob all the way to the left and record your reading ____________________.
Turn the knob all the way to the right and record your reading ____________________.
Connect the red probe to 2 and the black probe to 3 and record your reading
_________________________.
Turn the 1k Ohm knob and explain what you see happening ______________________________
Turn the knob all the way to the left and record your reading _____________________.
Turn the knob all the way to the right and record your reading _____________________.
Now look at your results and try to explain what you have just observed with the different holes and
your measurements.
Get your teacher's initials before moving on __________________________.
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59
Electricity Unit
Having FUN with Ohm's Law!
You've learned from our experiments with series circuits that the voltage across each light bulb
added up to the voltage of the battery. We're going to explore why that happens. At this point you
have the skills, tools, and knowledge to create your own experiments with just a little bit of help.
Experiment 1:
Use your battery and 2 resistors (make sure they are the same value) and measure the
voltage of the battery and across the resistors, the actual resistances of the resistors, and
current(s). It'll be easier to measure the resistances before creating your circuit. Using Ohms law,
explain what you saw.
Battery voltage:
volts
Current through the circuit:
amps
Resistor 1 resistance:
ohms
Voltage across Resistor 1:
volts
Resistor 2 resistance:
ohms
Voltage across Resistor 2:
volts
Experiment 2:
Repeat experiment #1 with 2 resistors of different values and explain what you see
happening.
Battery voltage:
volts
Current through the circuit:
amps
Resistor 1 resistance:
ohms
Voltage across Resistor 1:
volts
Resistor 2 resistance:
ohms
Voltage across Resistor 2:
volts
What happens when the resistors are put in a parallel configuration?
Experiment 3:
Repeat experiment 1 but with the resistors in parallel and explain your observations.
Battery voltage:
volts
Resistor 1 resistance:
ohms
Voltage across Resistor 1:
volts
Resistor 2 resistance:
ohms
Voltage across Resistor 2:
volts
Current resistor 1:
amps
Current through resistor 2:
amps
Experiment 4:
Repeat experiment 1 but with the resistors in parallel and explain your observations.
Battery voltage:
volts
Current from battery into circuit:
amps
Resistor 1 resistance:
ohms
Voltage across Resistor 1:
volts
Resistor 2 resistance:
ohms
Voltage across Resistor 2:
volts
Current resistor 1:
amps
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Current through resistor 2:
amps
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