Day 1QOD: Before electricity reaches your home, where does it originate from?

Electrical generating plants

Agenda:1. QOD & Measurement2. Introduction to Electrical Circuits - PP3. Activity – Atomic Theory4. 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

Tree Map

Atomic Theory

Conductor Semi-Conductor Insulator

Day 2QOD: What must an electrical current contain at a minimum?

Voltage source, load and conductors

Agenda:1. QOD & Measurement2. Introduction to Electrical Circuits - PP3. Activity – Ohm’s Law Problems4. 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 resistance is _____.

2. If the resistance of a circuit is 25 ohms and the current is 10 amps, the power in 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. What is the applied voltage of a circuit that has 10 amps of current and 12 ohms of resistance?

5. What is the applied voltage if the current in a circuit is 60 amps and the resistance is 10 ohms?

6. How many amps are there in the current of a circuit if the voltage source is 140V and the resistance is 2 ohms?

7. A circuit has a source voltage of 50V and a current of 10A. What is the power in watts?

5

2500

4 Ohms

120 Volts

600 Volts

70

500

Day 3QOD: What are two types of resistors?

Wire-wound and Carbon composition

Agenda:1. QOD & Measurement2. Introduction to Electrical Circuits - PP3. Activity – Electrical Measuring Instruments4. 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 series-parallel 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 clamp-on 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 de-energized.

• 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

Tree Map

Electrical Measuring Instruments

Multimeter Ammeter Voltmeter Ohmmeter Voltage tester

Day 4QOD: 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 wattsAgenda:1. QOD & Measurements2. Safety Pledge3. Review for Test – Introduction to Electrical Circuits

Review Questions – p. 22Trade Term Quiz – pp. 23-24Supplemental Exercises – pp. 25-26

4. Review

SkillsUSA Announcements:1. Membership Deadline – September 12th

Day 5QOD: What is an ohmmeter is used to measure?

resistance and to check continuity in circuits.

Agenda:1. QOD & Measurements2. Safety Pledge3. Review for Test – Introduction to Electrical Circuits

Review Questions – p. 22Trade Term Quiz – pp. 23-24Supplemental Exercises – pp. 25-26

4. Review

SkillsUSA Announcements:1. Membership Deadline – September 12th

Day 6QOD: What are some examples of good conductors?

Copper & silver

Agenda:1. QOD & Measurements2. Safety Pledge3. Test – Introduction to Electrical Circuits4. Review

SkillsUSA Announcements:1. Membership Deadline – September 12th