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Introduction
In this investigation, students will explore concepts of electricity. By using a voltage
sensor attached to a computer, students will be able to investigate aspects of battery and
bulb function and behavior, and gain insights into the operation of many everyday items
that use electrical energy.
In addition, students will gain experience with content and inquiry concepts, including:
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Realizing that electrical circuits can produce light, heat, sound.
Discovering that electrical circuits require a complete loop through which an
electrical current can pass
Asking a question about objects used in their daily lives
Employing simple equipment and tools to gather data
Using data to construct a reasonable explanation.
Understanding the process of measurement and units.
Using representations to model and interpret physical, social, and mathematical
phenomena.
Collecting data using observations, surveys, and experiments.
Recognizing and applying mathematics in contexts outside of mathematics.
Discussion Guide (TBD)
Unit 2 is a Physical Science Unit on the topic of Electricity. One of the main points of
the unit is to introduce students to some beginning concepts regarding electrical energy
and give students a foundation upon which to build.
Investigation 1 begins with students thinking about every day items that use electrical
energy and how that energy can convert to light, heat, sound and motion. The first use of
the sensor involves measuring voltage of a collection of batteries. The batteries do not
need to be new and having many different kinds of batteries is fine. While not explicit in
the activity, once the students have measured voltage, they can look on the battery to see
what voltage the battery is supposed to produce. Through this, students think about new
and “used up” batteries.
Some things to watch for in Investigation 1 include:
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Batteries have terminals. On many smaller batteries, the terminals are on the
ends. When making a simple circuit, students will need to realize that if wires do
not contact the terminals, the circuit will not work.
Batteries have orientation, meaning there is a positive (+) end of a battery and a () end. If students have ever placed a battery in a game, flashlight or walkman,
they may be familiar with this concept. If batteries are installed improperly, often
electronic items do not function. When using a simple circuit with a battery and
a light bulb, orientation does not affect the function of the bulb. However, when
you introduce a voltage sensor, the measured voltage will be negative if the poles
are reversed. One of the simplest ways to deal with this is to teach students to put
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the red lead on the positive (+) end and the black lead on the other end. On most
batteries, the negative end is flat and the positive end has a bump.
Most low voltage batteries require an understanding of a decimal place. An AA
battery typically produces around 1.5 volts. If the investigation rounded all
measurements to the nearest integer, readings would be misleading. Rounding to
the nearest 10th is acceptable for an accuracy standpoint, which is what the CC
Portfolio does for this Unit. Some discussion of the decimal point may be needed
depending upon your students level of understanding.
Investigation 1 finishes with a look at conductors and insulators. Students need to design
a test circuit to determine whether something is a conductor or insulator. They should
check with the teacher to determine whether or not to proceed with their design. In the
suggested answers, a working design is pictured. Basically, the design should use the
material in one part of a series circuit with a battery and a bulb. If the material is a
conductor, the bulb will light, otherwise it will not.
Additional Teacher Background
Electricity can be an illusive topic to understand, especially in 3rd and 4th grade. The goal
of this unit is not be to try to explain too much, but at the same time try to set a
foundation that is something that can successfully be built upon. Some aspects of the
study of electricity that can be confusing or incorrect are listed below.
Common Misconceptions
1. Use of the word “electricity.” Electricity, by dictionary definition, means several
things, some of them conflicting. As an example of this, a published assessment
question on the topic of electricity is as follows:
“When an electric lamp is lighted, what happens to the electricity that goes into
the bulb?”
If you think of electricity as electrical energy, the answer would be that some of
the electrical energy is converted to radiation in the form of heat and light. This is
how the electric company thinks of the electricity that they sell us on a daily basis.
However, the intention of the question (according to publishers answers) is to
establish that current is constant across a resistance such as a bulb. In this case,
the term “electricity” to refer to electric current.
The safest way to use the word “electricity” is to use it in reference to the field of
study. Do not use it to refer to energy, current, power or other terms within the
field of “electricity.”
2. Electric energy is carried by individual electrons. Electrons move very slowly in
a circuit (centimeters per minute), while the electrical energy moves nearly
instantaneously. Many metals (conductors) are full of a sea of movable electrons.
If electrons are pumped at one point in the circuit (a battery), then electrons
within the entire circuit are forced to move, and energy spreads throughout the
circuit almost immediately.
3. “Electricity” which flows in wires is supplied by batteries or generators. The
term “electricity” needs to be refined to something meaningful, since “electricity”
has multiple meanings. Electric currents in copper wires are a flow of electrons,
but a battery or generator does not supply the electrons. Instead, the electrons
come from the wire. Batteries and generators cause electric charge to flow. A
battery or generator is like your heart. It moves blood, but it does not create
blood.
4.
“Electric Current” flows in wires. An electric current is the result of a flowing
substance, but the name of the substance is not “current.” Rather, the name of the
substance is called “charge.” An electric current is a flow of charge.
The misconception that results is that when current stops flowing, what do the
wires have in them? It would seem that they have nothing in them and to get the
current flowing again, you would need to use some form of “current source” like
a battery to get things going. This is all incorrect.
Consider a river. It has a current. The current results from the flow of water. If
the current stops, the river is still full of water. With a little push, the water will
start flowing again.
This is analogous to the electric circuit. The wires are always filled with charge,
since that is what a wire/conductor is – it’s a substance filled with moveable
charge. A battery supplies a push, the charge starts moving resulting in a current.
The circuit is broken or the battery is removed, and the current stops. The wire is
still filled with charge, it’s just not moving.
5. Electrical current is a flow of energy. Electric current is a very slow flow of
charge. In AC circuits, this flow of charge vibrates back and forth. In DC
circuits, it flows in one direction. Energy flows in both types of circuits nearly
instantaneously. In any given circuit, two things are flowing: Charged particles
and Energy.
An Analogy
An analogous working model of a circuit is as follows:
This “Circuit Board” is made of a piece of cardboard, 4 flexible straws, a piece of kite
string and some packing tape. The “wire” in the circuit is composed of straws with kite
string in them. In the picture above, straw and string are the wire of the circuit, and the
hand is the battery. Note that the straw and string are not analogous to a wire and its
insulation – the straw and the string are analogous to the wire. The string indicates
electrical charge, which is movable within the conducting wire (straw).
The principles that the model helps convey are as follows:
1. The meaning of a battery. A battery pumps charge within a circuit. The hand
moving the string above is analogous to a battery. The hand is not creating the
string, it is simply moving it. A battery does not create charge, it simply moves it.
As a result, when a battery stops pushing charge, the charge stops moving, but it
does not go away. In the model above, if the hand ceases to push the string, the
string stops moving, but it does not go away. This is a concept that many
analogies of electricity do not communicate well.
2. When a battery or generator pushes charge, energy moves instantaneously
throughout the circuit. An important concept that is often poorly explained is
that as soon as a battery starts pushing charge, electrical energy is present
throughout the entire circuit. Some texts explain that the battery pushes charge
(electrons) and that the electrons carry the energy. If this were the case, it would
take a long time for that electron to carry energy to the place it was needed in the
circuit. In reality, this energy is available almost instantaneously. In the above
model, as soon as one part of the string is pushed, all parts are moving
instantaneously. If you add a motor to the circuit, as shown below, as soon as one
part of the string is pushed, the motor immediately starts to turn because all parts
of the string immediately start to move. This occurs even though the piece of
string that was initially moved does not make its way to the motor for a while.
The “motor” is made up of a pushpin and a
post-it note. The pushpin is wrapped once
with the string and as soon as the string
moves at all, the “motor” begins to turn. In a
real circuit, as soon as charge begins to
move, electrical energy is present and can
power things. Note that this model also
works for AC circuits. Moving the string
back and forth will move the motor, even
though the string goes nowhere but back and
forth.
3. Electrical circuits need to be closed loops. The above circuit would not
function without a loop. If the string is cut, pushing one part of the string will not
cause the motor to turn and will not cause the entire string to move. If the string
is cut, it will not work.
4. The concept of resistance. Instead of the motor, another student can resist the
movement of the string or “flow of charge.” This resistance makes it more
difficult for the student moving the string or the “battery.” If the student moving
the string moves it quickly enough, the student who is resisting can also feel the
heat created by the energy of the string passing through his or her resistance.
Analogies that can be misleading
One student activity that is done to give students an idea of how a circuit behaves is
described as follows. Students form a circle holding hands. One student is the battery,
and one student is a light bulb. The “battery” student squeezes his or her left hand.
Feeling this squeeze, the next student over transfers this squeeze to the next person, and
so on around the loop. The “light bulb” student, when her hand is squeezed, smiles
brightly indicating that the light has been lit. The hand squeezing continues all the way
back to the battery.
The biggest problem with this analogy is that it mixes the flow of electrons with flow of
energy – they become one and the same, moving together at the same speed. Energy in a
circuit does not flow in a circle, it flows from battery to bulb, or from the source to
whatever is transforming the energy into some other form of energy. So the hand
squeezing is not analogous to energy. However, if it is meant to be analogous to the flow
of charge, or current, the bulb should not wait until the charge arrives. Rather, it will
light as soon as charge starts moving at all.
To add to the problem, the model is taken a step further where one person in the circle
“breaks the circuit.” This creates a situation where the hand squeezing does not make it
all the way around the circle and it is determined to be an open circuit. In reality, as soon
as the circuit opens, all hand squeezing would immediately cease, since there is no
current and no movement of charge in an open circuit.
Another poor analogy is one where a circuit is likened to a train on tracks. The electrons
within a circuit as said to be train cars, which carry coal from a battery (the coal supplier)
to a bulb, which burns the coal. The train then returns to the battery to reload with coal,
completing the circuit.
This analogy implies that the electrons carry the energy, which is not true. The motion of
the electrons creates the energy, but the electrons do not carry the energy.
Neither of the above two models do well in an AC circuit situation, although the one
proposed for this Unit functions well in an AC situation.
Suggested Timeline
The amount of time you spend on introductory discussions, data collection and analysis
will determine your overall timeline. The following represents a possible timeline
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One half class period – “Setting Up” discussion
One class period – Trial I: Messing around
One class period – Trial II: Light a holiday bulb using a battery
One class period – Trial III: What is a conductor?
One class period – Analysis and “Wrap Up” discussion