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Current Electricity Unit Overview

The Current Electricity Unit is intended to engage
students in myriad experiences with hands-on and computer-based materials
that will help them modify their existing ideas and construct new ideas
about current electricity.  The unit begins with an introduction
to electrical devices, to help students realize that electrical devices
are not magical, but they are simply loops of conductors and non-conductors. 
From this basis, Cycle II starts to develop ideas of flow of charge
and push on charge, and how series and parallel circuits are different. 
Cycle III introduces the capacitor and the origin of charges as everywhere
in conductors.  Cycle IV develops a full model of series circuits,
and a more sophisticated idea of resistance and flow.  Students
are also introduced to the idea of electrical pressure differences. 
In Cycle V, students pull together all the ideas to explain parallel
circuits and series-parallel circuits.

The Unit consists of five
cycles:

Cycle I: What Are the Conditions
Necessary to Light the Bulb?

Cycle
II: Beginning To Build A Conceptual Model (effect of bulbs and

batteries
in a circuit)

Cycle III: What is the Location
of the Charges that Flow in a Circuit?

What Causes the Charge to Move?

Cycle IV: What Effect Do Bulbs
and Batteries Have on the Movement of

Charge in Series Circuits?

Cycle V: How Does Charge Flow In
Parallel Circuits?

Target Ideas for Unit

The Current Electricity Unit was designed to provide
the opportunities for students to construct ideas, which are closely
aligned with the ones listed below.  At the end of each activity
in the Development Phase, students are asked to add or modify an idea
in their Idea Journal, based on evidence gathered within that activity. 
We have found this semi-structured approach for development of a common
set of ideas to work well with high school students, prospective and
in service elementary teachers.  Naturally, as part of their consensus
discussion for each cycle, students will probably develop these ideas
in their own words.  However, the conceptual content of their own
ideas should be similar to these.  The Teacher Guide for each cycle
provides examples of the kinds of statements students actually develop
in the class. After the class agrees on a set of ideas the teacher should
introduce appropriate terminology and conventions so that the students'
are more closely aligned with the corresponding ideas they would find
in textbooks or when they talk with other students.

Target
Ideas for Cycle I

Conductor/nonconductor Idea: Things made of metal material seem to conduct. 
Most other materials seem to insulate or not conduct well.


Two-endedness Idea: Each electrical device seems to have two conducting
ends or connection points (terminals).  Each connection point must
be involved for the device to function in lighting the bulb.


Path of Conductors Idea: There needs to be a continuous loop of conducting
material all the way from one end of the battery through each of the
electrical devices to the other end of the battery for all the devices
to function in lighting the bulb.  The bu</span><span class="Normal--Char" style=" font-family: 'Times New Roman', 'Arial';
font-size: 12pt;">lb will light when (1) the bulb filament is part
of a continuous loop of conductors from one end of the battery to the
other, and (2) there is no other loop of conductors from one end of
the battery to the other that does not go through the filament. 


Purpose of nonconductors Idea: The purpose of the nonconductors in the construction
of bulbs, sockets, battery holders and switches is to prevent the possibility
of a second path of conductors that does not go through the bulb filament
(which would cause t</span><span class="Normal--Char" style=" font-family: 'Times New Roman', 'Arial';
font-size: 12pt;">he bulb to go off).


Talking science: Mental models are the abstractions (ideas) we build
to help us make sense of the phenomena we observe.  Observations
are statements or recorded measurements that represent something you
can actually sense (see, hear, touch, taste, smell). Inferences are statements that represent something
that requires mental modeling or a logical conclusion.


Operational Definitions: An operational definition is a set of criteria
(a sort of recipe) for determining something.  Operational definitions
in this cycle include: A circuit is closed when there is a continuous
loop of conductors from one end of the batt</span><span class="Body-0020Text-0020Indent-00203--Char" style=" font-family: 'Times New Roman', 'Arial';
font-size: 12pt;">ery to the other end of the battery.  A circuit
is open when there is no continuous loop of conductors from one side
of the battery to the other.  A closed circuit is called a "short"
circuit when there is a continuous loop of conductors from one end of
th</span><span class="Body-0020Text-0020Indent-00203--Char" style=" font-family: 'Times New Roman', 'Arial';
font-size: 12pt;">e battery to the other that does not go through a
bulb filament.

Target Ideas for Cycle II

Bulb as resistance Idea: The filaments of bulbs create a resistance to the
flow of electricity. In a short circuit this flow seems to take the
easiest path through the wire without a filament.


Bulb brightness Idea: As bulbs are added in series, the bulbs glow equally
dimmer and dimmer.  As bulbs are added in parallel, each bulb glows
with the same brightness as a single bulb.


Battery and flow of electricity
Idea: The greater the number of batteries connected (+)
to (-) in a circuit, the greater the flow of electricity in the circuit.


One direction flow Idea: One kind of electricity seems to flow from one end
of the battery to the other end in closed circuits.


Operational definitions: We call a closed circuit with only one bulb a "single-bulb" circuit.  For multi-bulb circuits, we
can define different kinds of closed circuits: A circuit is a series circuit when the bulbs are all in the same continuous
path of co</span><span class="Normal--Char" style=" font-family: 'Times New Roman', 'Arial';
font-size: 12pt;">nductors.  A circuit is a parallel circuit when each bulb has its own conducting path. 
A series circuit is called a "shorted-bulb" circuit when there is a path of loop of conductors
around one (or more) of the series bulbs that does not go through the
bul</span><span class="Normal--Char" style=" font-family: 'Times New Roma