Day 1
QOD: Before electricity reaches your home, where does it originate from?
Electrical generating plants
Agenda:
1. QOD & Measurement
2. Introduction to Electrical Circuits - PP
3. Activity – Atomic Theory
4. Review
SkillsUSA Announcements:
1. Membership Deadline – September 12th
Introduction to Electrical Circuits
Learning Targets:
•
•
•
•
•
Students will define voltage and identify the ways in which it can be
produced.
Students will explain the difference between conductors and
insulators.
Students will define the units of measurement that are used to
measure the properties of electricity.
Students will identify the meters used to measure voltage, current,
and resistance.
Students will explain the basic characteristics of series and parallel
circuits.
Introduction
• An electrical circuit contains at a minimum
– a voltage source
– a load
– and conductors to carry the electrical current.
Introduction
• The circuit should also have a means to start
and stop the current, such as a switch.
• The relationships among current, voltage,
resistance and power are common to all
electrical and electronic circuits.
– Voltage is defined as the force that causes
electrons to flow.
– Voltage is the driving force that makes current
flow in a circuit.
• Video – Power Distribution– (1:00)
Atomic Theory
• Atomic theory explains the construction and
behavior of atoms.
– including the transfer of electrons that results in
current flow.
• The simplest atom, hydrogen, is composed of a
nucleus containing a proton and a single
orbiting electron.
• An electrical current is created by the flow of
electrons.
– an electron has a negative charge
– a proton has a positive charge
Atomic Theory
• An atom can gain or lose electrons.
– If an electron is lost, the atom exhibits a positive
charge.
– A gain of electrons produces a negatively charged
atom.
• The nucleus is the central part of the atom and is
made up of protons and neutrons.
Atomic Theory
Atomic Theory
• Unlike charges attract each other and like
charges repel each other. This concept is
fundamental to the flow of electrical current.
Atomic Theory
• The outer shell of an atom, called the valence
shell, contain valence electrons that determine if
a substance is a conductor, an insulator, or a
semiconductor
Atomic Theory
• Conductors
– have fewer valence electrons than insulators and
semiconductors.
– are materials that readily conduct electricity.
– gold, silver, and copper are excellent conductors.
• Insulator
– is the opposite of a conductor, do not conduct electricity
– rubber, glass, porcelain, and some plastics are good
insulators.
• Semiconductors
– are a class of materials such as silicon and germanium
that are neither good conductors nor good insulators.
• Video – Ex. of Conductors and Insulators– (2:30)
Atomic Theory
• The operation of many electrical devices relies on
the principle of magnetism.
– A magnet generates a magnetic field within which other
magnetized objects can be repelled or attracted.
• Electrical current flowing through a conductor also
produces a magnetic field.
– If the conductor is wrapped around an iron bar, an
electromagnet is produced.
Electric Power Creation & Distribution
• Electricity comes from generating plants that burn
fossil fuels, use nuclear energy, or use hydroelectric
(water) energy.
• Video – Power Distribution– (1:00)
Electric Power Creation & Distribution
Electric Power Creation & Distribution
• Devices called transformers are used to:
– boost the power to high levels so it can be moved over
long distances
– step voltage down to lower levels before it reaches a
home or office
• The power supplied to homes is stepped down to
240 volts.
• Commercial buildings may receive power as high as
575 volts.
Electric Power Creation & Distribution
Activity:
Atomic Theory
Objective: Understand the facts about
conductors, semiconductors and insulators.
Individual Task: Prepare a Tree Map to classify facts
about conductors, semiconductors, and insulators .
Be prepared to present your work to the class.
(Module 26103-11 / pp.2,3)
CLASSIFYING
Atomic Theory
Conductor
Semi-Conductor
Tree Map
Insulator
Day 2
QOD: What must an electrical current contain at a minimum?
Voltage source, load and conductors
Agenda:
1. QOD & Measurement
2. Introduction to Electrical Circuits - PP
3. Activity – Ohm’s Law Problems
4. Review
SkillsUSA Announcements:
1. Membership Deadline – September 12th
Ohm’s Law
• Ohm’s Law states that resistance of a circuit is equal
to the voltage divided by the current.
• The voltage, current, and resistance values in any
circuit are closely related.
– Knowing this relationship is important for understanding
how electrical circuits operate.
Ohm’s Law
Electric Charge and Current
• Current is represented by the letter I
– Is measured in amperes, A
• Resistance is represented by the letter R
– is measured in ohms, Omega
• Voltage is represented by the letter E
– is measured in volts, V
• Active Figure – Ohm’s Law Circle– (1:00)
Ohm’s Law
• For example, a 120-volt circuit contains a 30-ohm
resistor. Current can be calculated by dividing the
voltage by the resistance for a current of 4 amps.
(120/30 = 4)
• The resistance of a circuit is equal to the voltage
applied to the circuit divided by the current in the
circuit.
• The applied voltage to a circuit is equal to the
product of the current and the resistance of the
circuit.
Schematic Representation of Circuit
Elements
• A schematic diagram is a shorthand way of
drawing an electrical circuit. Symbols are
used to represent the circuit components.
Schematic Representation of Circuit
Elements
Resistors
• The voltage drop across a known resistance
can be determined using Ohm’s Law.
• Two common types of resistors are carbon
composition and wire-wound.
Resistors
• Wire-wound
• consists of a length of nickel wire wound on a ceramic
tube and covered with porcelain
• resistance value is printed on the resistor itself.
• more rugged and able to survive much larger power
dissipation
• Carbon composition
• constructed by molding mixtures of powdered carbon and
insulating materials into a cylindrical shape
• a color code is used to identify the resistance value and
tolerance
Resistors
Resistors
• The first three bands represent the resistance
value. The fourth band is the tolerance, which
will be either silver for 10% or gold for 5%.
Problems:
Ohm’s Law
1.
If a circuit has 48 amps of current and an applied voltage of 240 volts, the
5
resistance is _____.
2.
If the resistance of a circuit is 25 ohms and the current is 10 amps, the power in
2500
watts is _______.
3.
A 5-ohm and a 20-ohm resistor are connected in parallel. What is the total
resistance of these two resistors? 4 Ohms
4.
What is the applied voltage of a circuit that has 10 amps of current and 12 ohms
of resistance? 120 Volts
5.
What is the applied voltage if the current in a circuit is 60 amps and the
resistance is 10 ohms? 600 Volts
6.
How many amps are there in the current of a circuit if the voltage source is
140V and the resistance is 2 ohms? 70
7.
A circuit has a source voltage of 50V and a current of 10A. What is the power in
Day 3
QOD: What are two types of resistors?
Wire-wound and Carbon composition
Agenda:
1. QOD & Measurement
2. Introduction to Electrical Circuits - PP
3. Activity – Electrical Measuring Instruments
4. Review
SkillsUSA Announcements:
1. Membership Deadline – September 12th
Electrical Circuits
• Circuit descriptions such as series and parallel
refer to the way loads are connected in the
circuit.
• Series Circuit
– all loads are tied together like links in a chain.
– the total resistance of the circuit is the sum of all the
resistances in series.
• Parallel Circuit
– all loads are connected across the voltage source like
rungs in a ladder.
– the total resistance is always smaller than the
smallest resistor in the circuit.
– in a parallel circuit, the voltage drop is the same
across all loads.
Electrical Curcuits
• Series-parallel circuits
– both series and parallel circuits in one combined
hybrid circuit.
• To determine the total resistance of a seriesparallel circuit, first find the total resistance
of the parallel circuits, then treat that total
resistance as another series resistor and add it
to the other series resistors in the circuit
Electrical Curcuits
Measuring Instruments
• Test meters are often used by electricians to
measure voltage, current, and resistance.
• Meters that can measure voltage, current, and
resistance are called multi-meters.
– They are available in digital and analog versions.
Measuring Instruments
Measuring Instruments
• Because theses meters are often used on live
circuits, it is important to know the applicable
safety procedures.
• To read currents above the milliamp range,
electricians use an instrument called a clampon ammeter.
• To measure current with a clamp-on ammeter
the jaws of the ammeter are clamped around
the current-carrying conductor.
– The magnetic field in the conductor induces a
proportional current in the meter.
Measuring Instruments
Measuring Instruments
• An in-line ammeter is used to measure
current.
– It is connected in series with the load, never in
parallel. This is not a common practice.
Measuring Instruments
• A voltmeter is connected in parallel with the
load. Voltage is read with power applied.
Measuring Instruments
• An ohmmeter has a built-in battery power source,
and must always be used with the circuit deenergized.
• An ohmmeter is used to measure resistance and to
check continuity in circuits.
Measuring Instruments
• A continuity tester is a simple, battery-operated
device that can check circuit continuity. It is unable
to measure resistance.
• A voltage tester is a simple device that is used to
check for the presence or absence of voltage.
– always make sure voltage is tuned off before touching
any terminals
Electrical Power
• Power is defined as the rate of doing work.
• In electrical circuits, power is measured in
watts. One watt represents the work done in
one second by one volt moving one ampere.
Electrical Power
• Power can be calculated by multiplying the
voltage times the current.
• Mechanical power is measured in horsepower,
which can be converted to watts by multiplying
the horsepower rating by 746.
• The kilowatt hour (kWh) is the common unit of
measure for electrical power. Electric meters on
buildings are calibrated that way.
• If you have a 20-volt supply and a load current
of 20 amps, the power would be 2.4 kW. In five
hours, you would use 12 kWh of power.
Electrical Power
• As shown in the text, the power formula
variations of the P = E x I formula can be
used to solve for any of those values if the
other two are known.
Electrical Power
• Every resistor or resistive device has a
maximum power rating. If this rating is
exceeded due to excessive current, the
component will overheat and be damaged.
• The heat created by current flow through a
resistor is known as its I2R loss, which is the
power loss expressed in watts.
• If the power rating of a resistor is known, the
maximum current can be calculated by
rearranging the power formula.
Activity:
Electrical Measuring Instruments
Objective: List important facts about electrical
measuring instruments.
Individual Task: Prepare a Tree Map to classify facts
about electrical measuring instruments. Be prepared
to present your work to the class. (Module 26103-11
/ pp.15-17)
CLASSIFYING
Electrical Measuring Instruments
Multimeter
Ammeter
Voltmeter
Ohmmeter
Tree Map
Voltage tester
Day 4
QOD: What is the definition of Power and what is the unit that it is
measured by?
defined as the rate of doing work; measured in watts
Agenda:
1. QOD & Measurements
2. Safety Pledge
3. Review for Test – Introduction to Electrical Circuits
Review Questions – p. 22
Trade Term Quiz – pp. 23-24
Supplemental Exercises – pp. 25-26
4. Review
SkillsUSA Announcements:
1. Membership Deadline – September 12th
Day 5
QOD: What is an ohmmeter is used to measure?
resistance and to check continuity in circuits.
Agenda:
1. QOD & Measurements
2. Safety Pledge
3. Review for Test – Introduction to Electrical Circuits
Review Questions – p. 22
Trade Term Quiz – pp. 23-24
Supplemental Exercises – pp. 25-26
4. Review
SkillsUSA Announcements:
1. Membership Deadline – September 12th
Day 6
QOD: What are some examples of good conductors?
Copper & silver
Agenda:
1. QOD & Measurements
2. Safety Pledge
3. Test – Introduction to Electrical Circuits
4. Review
SkillsUSA Announcements:
1. Membership Deadline – September 12th