Student Learning Objectives. Instruction in this lesson should result in
students achieving the following objectives:
1 Explain electricity and how electricity flows along a complete circuit.
2 Describe the components of a complete electrical circuit.
3 Explain the functions of conductors and insulators and identify common
conductors and insulators used in agricultural facilities.
Illinois Physical Science Applications in Agriculture Lesson B4–2 • Page 1
Anticipated Problem: How is electrical energy controlled?
I. Electricity is a flow of electrons along a conductor. The conductor is the path along
which the electrons flow. For such a flow to exist, it is necessary that there be a complete
circuit. The complete circuit must allow for the electricity to flow from the source to the
load and back to the source.
A. A conductor is a piece of metal in the form of a wire. Metals are excellent conductors
B. The circuit is a path for electrons to move through components and wires. Electrons
moving in a negative to a positive direction along a conductor is current.
C. Direct current flows in one direction only, from source to load. Alternating current
involves a change in direction by the electrons, occurring at a rate of 60 times per second
or 60 hertz. All residences in the United States use alternating current in their circuits.
Anticipated Problem: What is necessary for a complete electrical circuit?
II. To have an electrical circuit, there must be a source of applied power, a load to which
the power is applied, a path for the electrons to pass from the source to the load, and a
return path for the electrons to pass from the load to the source.
A. A switch is used as a means to control the electron flow.
B. Overcurrent protection in the form of a fuse or circuit breaker is added for safety.
Illinois Physical Science Applications in Agriculture Lesson B4–2 • Page 3
Anticipated Problem: What is an insulator and a conductor and what determines if a
substance is an insulator or a conductor? What is a semiconductor?
III. All materials may be classified as either conductors of electricity, non-conductors of
electricity (insulators), or partial (semi) conductors of electricity. Atoms of conductors
give up electrons resulting in electron flow. By surrounding a conductor with an insulator
electron flow can be controlled and used. Insulators are non-conducting material lacking
a sufficient supply of free electrons to allow for movement of current through the
A. Semiconductors have resistivity values between those of insulators and conductors.
Silicon is an example of a semiconductor. The electrons in semiconductors are bound
more strongly than in conductors, but less strongly than in insulators.
B. The electrical properties of semiconductors can be controlled by adding other elements
to alter their structure and change their electrical properties. These altered
semiconductors are the basis of all modern electronic circuits. Semiconductors are used
to make transistors, integrated circuits, and chips for microelectronics.
CONTROLLING ELECTRICAL CURRENT:
CIRCUITS, CONDUCTORS, AND
Part One: Matching
Instructions: Match the word with the correct definition.
a. insulator d. current
b. direct current e. conductor
c. complete circuit f. circuit
_______1. Solid, liquid, or gas that permit the flow of electrons.
_______2. A path for electrons to flow from the power source to the consuming device and back
to the power source.
_______3. Non-conducting material lacking a sufficient supply of free electrons to allow for
_______4. A path for electrons to move through components and wires.
_______5. Movement of electrons in a negative to positive direction along a conductor.
_______6. Current that flows in one direction only.
Part Two: Fill-in-the-Blank
Instructions: Complete the following statements.
1. __________ and __________ are the most common metals used as conductors in electrical
2. A material that creates a path in which electrons flow is called a/an __________.
3. Insulators have a resistance level that is __________.
4. Electrons change direction of flow frequently in __________ __________.
Illinois Physical Science Applications in Agriculture Lesson B4–2 • Page 6
Part Three: Multiple Choice
Instructions: Write the letter of the correct answer.
_______1. Dry _____ or _____ resist the flow of electrons through it, making it a poor conductor.
a. sand and soil
b. soil and water
c. water and air
d. none of the above
_______2. Which of the following would be considered the best conductor of electricity?
_______3. A material that inhibits the flow of electrons is called a/an _____.
Part Four: Short Answer
Instructions: Answer the following statements.
1. Compare and contrast alternating current and direct current.
2. Identify the four main components of a complete electrical circuit.
Illinois Physical Science Applications in Agriculture Lesson B4–2 • Page 7
1. What is an insulator?
An insulator does not conduct electrical current and provides safety by covering
wires and other electrical equipment with a non-conducting material. The purpose
of an insulator is to prevent shocks and short circuits. Even though insulators are
capable of providing protection, they may not always be adequate due to misuse,
abuse, or deterioration. Insulators can be made up of plastic, rubber, or any other
nonmetallic material. Insulators must meet the type of material and thickness recognized
in the National Electrical Code.
2. What is a conductor?
A conductor allows for the flow of electrons in the direction from negative to positive
charge. The positive end of the circuit attracts the negative flow of electrons.
Conductors can be of solid, liquid, or gas state. Types include:
most popular conductor due to conductivity and cheap cost.
common household wiring element.
provides safe, trouble-free service, and easily installed.
Illinois Physical Science Applications in Agriculture Lesson B4–2 • Page 20
conducts better than copper but too expensive.
high strength for its light weight.
used for high power lines and service drop locations.
bare aluminum wires form aluminum oxide on outer surface which acts as an
insulator, causing heat to build up in current.
failures occur at temperature changes, humidity, vibrations, corrosion with
Brass, Iron (Fe), and Zinc (Zn)
fair conductivity but seldom used in today’s wiring.
used to help prevent aluminum oxide buildup on power lines.
3. What determines if a substance is an insulator or a conductor?
Electrons either orbit close to the nucleus or far from the nucleus of the atom.
Atoms of elements such as copper, aluminum, and other metals have electrons
which orbit far from the nucleus and are not held tightly to the atom. Because these
atoms can move freely from one atom to another, they will conduct an electric current.
On the other hand, insulators have electrons which orbit closer to the nucleus
and are held tightly to the atom. These atoms cannot move as freely from one atom
to another so they do not conduct an electric current.
4. How is electrical energy controlled?
Electricity always flows from negative to positive along a conductor or path. Electrical
energy can be controlled through the use of insulators and other overcurrent
5. What is necessary for a complete circuit?
A complete circuit is required for electron flow to occur. A complete circuit requires
the following: 1) Source of electrical pressure or force for current 2) A path for the
electron flow 3) A load which converts electrical energy to heat, light, and power for
a specific function 4) A switch to control the circuit 5) Overcurrent device for protection
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