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Applied TechnologyLevel 2

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2 • Applied Technology

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Applied Technology • 3

2Hi! My name is EdWIN. I will be your guide

through this course. You may remember mefrom Level 1. This is the second of six levels ofApplied Technology. Watch for me as I try to helpyou along with tips about what you are studying.

Applied Technology will help you understandbasic concepts about heat, fluids, mechanics, andelectricity. Don’t worry. I am going to makeeverything as simple as I can. You can move atyour own pace. We will start with a review ofsome basics from Level 1. Hopefully, you willremember or already know this information.

In this level, you will study basics aboutelectricity. We will see how some principles applyto everyday life. This will help you get ready tolearn more difficult material in higher levels ofApplied Technology.

Now that I have told you a little about thiscourse, are you ready to go? OK, then let’s begin!Hi, I’m EdWIN!

INTRODUCTION


2At Level 2 you should be able to:

• define the word technology.

• discuss basic principles and laws of nature.

• recognize basic forms of matter.

• define energy.

• know basic principles of heat.

• explain the concept of pressurized liquids andgases.

• define machine.

• discuss the inclined plane.

• discuss the lever.

PREREQUISITE SKILLS


2In this level you will:

• apply basic principles of thermodynamics.

• apply basic principles of fluid dynamics.

• apply basic principles of mechanics.

• describe basic types of electricity.

• describe basic principles of electricity.

• discuss the paths of simple electrical circuits.

• learn to use Ohm’s law.

• explore basic principles about direct-current electricity.

• explore basic principles about alternating-current electricity.

LEARNING OBJECTIVES


2LESSON 1 Applications of Level One Skills

LESSON 2 Basics of Electricity

LESSON 3 Direct-Current Electricity

LESSON 4 Alternating-Current Electricity

LESSON 5 Posttest

REFERENCE Glossary

Respect electricity. The authors and publishers of thiscourse are not responsible for accidents or injuriesresulting from the use of information in this book.

OUTLINE


2APPLICATIONS OFLEVEL ONE SKILLS

Let’s begin by using some basic applicationsof applied technology. In Level 1, we discussedsimple principles about heat and fluids. If yourecall, I said the study of heat is calledthermodynamics, and the study of fluids is calledfluid dynamics. I also introduced mechanics bytalking about the inclined plane and lever.

In this lesson, you will practice usinginformation about these basic principles. Youwill read about a workplace situation. Then youwill use what you know about appliedtechnology to suggest how to solve the problem.

Remember that technology simply means theuse of tools or methods to do work more easily.Now, let’s apply what you know.

LESSON 1


2EXERCISE – APPLICATIONS OF LEVEL ONE SKILLS

Instructions: Read each scenario. Then select the letter that represents the bestanswer to the related question(s).

1. You are replacing the handrails along a concrete walkway.A red light on the water-cooled drill you are operating keepsindicating the drill is overheating. What is most likely theproblem?

a. You are not able to operate the drill.b. The water level in the cooling system is low.c. The motor is malfunctioning.d. The light is malfunctioning.

2. You are trying to move a desk on a “dolly” into an officewhen you find that you cannot lift it up over a step. Youshould:

a. wait until you find someone to help you lift it.b. give up and call a moving company.c. take the desk apart and move it piece by piece.d. make a ramp with a piece of wood that you have in the

storeroom.

LESSON 1


23. You are operating a machine that creates friction. It has a

temperature gauge on it that you must monitor. The gaugeis reading in the red area that indicates danger zone. Youshould:

a. stop the machine and let it cool down.b. call the fire department.c. continue using the machine until it quits running.d. check to see if the power cord is frayed.

4. You are hammering a nail into a board, but the nail bends.You must pull it back out. You use a claw hammer to increasethe force you need to remove the nail. What simple machineprinciple is used by the claw hammer?

a. inclined planeb. leverc. screwd. gear

5. Your company, located in Valdosta, Georgia, is sponsoringa softball team in the summer league. You have been giventhe responsibility to purchase uniforms for the team. Whatwould most likely be the best color to select for the uniform?

a. redb. blackc. whited. dark green

LESSON 1


26. The process at the Westerland’s Cranberry Farm floods the

beds of mature berries. The cranberries are knocked offthe vine with beaters and float to the top of the water. Whatproperty of the berries causes them to float?

a. densityb. inertiac. compressiond. volume

7. You need to load a bathtub onto a delivery truck. What isthe mechanical advantage of using the following inclinedplane?

a. 6 to 1b. 2 to 1c. 3 to 1d. 12 to 1

6 ft

3 ft

100 lb

LESSON 1


28. How much force must you use to push the 100-lb tub up

the inclined plane?

a. 30 poundsb. 40 poundsc. 100 poundsd. 50 pounds

9. You are starting a summer job delivering refrigeratedproducts. The maintained temperature in the storagecompartment of your truck is 45˚. You notice that when youare making deliveries and you do not completely shut thetruck door, you see drops of water on some of the productswhen you return. What is causing this moisture to appear?

a. evaporationb. inertiac. condensationd. compression

10. You need to remove a panel from a piece of equipment thatis very old. The bolts used to secure the panel do not wantto budge. What step could you take to increase your abilityto remove the bolts?

a. Pour hot water over the bolts.b. Use a wrench with a longer handle.c. Use an insulated wrench.d. Turn the equipment upside down.

LESSON 1


2ANSWERS TO EXERCISE

1. Answer: b. The water level in the cooling system is low.The key word to identifying the problem isoverheating. The drill creates friction as it movesagainst the hard surface of the concrete. Thisspecial drill (core-drill) applies water to keep thedrill bit cool.

2. Answer: d. make a ramp with a piece of wood that you havein the storeroom.Using an inclined plane gives you a mechanicaladvantage. You must push the desk a fartherdistance using a plane, but you do not have to exertas much effort.

3. Answer: a. stop the machine and let it cool down.Friction causes heat. The gauge allows the operatorto know when the temperature is reaching a pointwhen damage could be done. Allowing the machineto cool will prepare it to run again. You should alsocheck proper operation of cooling and lubricationsystems.

DAN

GER

NO

RM

AL

HEA

TG

AU

GE

I need to find whatis causing this problem.

LESSON 1


24. Answer: b. lever

5. Answer: c. whiteThe summer temperatures in Georgia will mostlikely be hot. White uniforms will reflect heat fromthe sun. Darker colors will absorb heat and likelymake players uncomfortable.

6. Answer: a. density

7. Answer: d. 2 to 1

Effort

Fulcrum

Force

Nail

LESSON 1


28. Answer: d. 50 pounds

100 lb (weight to be moved)2 to 1 (mechanical advantage)

divide 100 by 2 to find the force needed with themechanical advantage of 2 to 1

9. Answer: c. condensationWarm air from outside seeps into the refrigeratedtruck and comes into contact with the cold products.The water vapor in the air becomes colder andbegins to change (condense) into tiny waterdroplets.

10. Answer: b. Use a wrench with a longer handle.A wrench with a longer handle will give you moreleverage. Also, if the bolt is rusty, you should firstuse a commercial product that is a liquid solvent todissolve the rust.

LESSON 1


2LESSON 1

This page was intentionally left blank.


2BASICS OF ELECTRICITY

Electricity is a very powerful form of energy.Electricity as a power source has many excellentfeatures. It is silent, invisible, clean, and can bemade to start or stop with the flip of a switch.Electricity is a vital power source for industry,our homes, and our pleasure. It provides theenergy for light, household appliances and tools,large and small motors, and even some cars arenow powered by electricity. While there are somepretty complex applications for electricity, thebasics are pretty simple. That’s where we’re goingto start. We’re going to explore the very basicsof electricity.

LESSON 2


2Types of Electricity

There are basically three types of electricity.Alternating current is normally referred to as AC.Direct current is normally called DC. There isalso static electricity.

Alternating current is a “pulsating” electricity.The speed that it pulsates is measured in cyclesper second (cps). The AC used in the UnitedStates pulses at 60 cps. Now you’ll probablyrecognize your household power and the labelson your appliances. The most common voltageis 120 volts AC @ 60 cps. Appliances in yourhome with larger power requirements will use240 volts AC @ 60 cps. These appliances includecooking ranges and ovens, clothes dryers, andcentral air conditioning. In some industrialapplications, much greater power will berequired than that for the home.

Cycles per second is also referred to as hertz.They mean exactly the same thing. Note that120 volts AC @ 60 cps is the same as 120 voltsAC @ 60 hertz (60 Hz). Another point ofinterest is that while the United States hasadopted a standard of 60 cps, other countriesmay have other standards. For example, manycountries in Europe use a standard of 50 cps. Asa result, appliances designed for use in the U.S.may not function properly in some othercountries. Fortunately, in some cases, adaptersare available to make them work.

LESSON 2


2Direct current is another type of electricity.

Unlike AC, which pulsates, DC has a constantlevel of electrical output. The most commonsource of DC is batteries. Batteries are used topower lights, tools, video games, automobiles,and many other items where portability isimportant.

In today’s electronic world, many devices useboth AC and DC. Appliances like your TV,stereo, and home computer use 120 volts AC asthe base power source. However, in the internalpower supplies of the appliances, the AC isconverted to smaller DC voltages, which in turnpower and control the miniaturized circuitry.

Static electricity occurs when certain typesof matter are rubbed together. This action createsan electrical charge. The example most of us haveexperienced is walking across a carpeted room,touching a doorknob, and receiving a mildshock. The friction of our shoes rubbing thecarpet created an electrical charge on our body,and the doorknob provided a discharge path.While we experienced a small shock, staticelectricity can be very powerful. Lightning is anexample of powerful static electricity. There aremany practical uses for static electricity; however,we are going to concentrate on the morecommon types of electricity, which are AC andDC.

LESSON 2


2Principles of Electricity

If we went into the scientific theories ofelectricity, we would encounter terms such asquarks, electrons, atoms, protons, neutrons,ions, particles, molecules, and so on. Since weare not trying to become scientists or engineers,we are going to stay very basic and only talkabout electrons.

Electrons exist in matter and are electricallycharged. They are either positively charged,negatively charged, or neutral. This idea formsthe basis for electrical current flow.

There are more

electrons in this

dot than there

are people on

this planet!

LESSON 2


2A magnet is surrounded by a magnetic field.

Have you noticed that when you bring twomagnets close together, they will either jumptogether and cling, or push away from eachother? This demonstrates how in magnetism,opposites attract each other and likes repel eachother. Let’s explain that a little differently. If Ihave two magnets in the shape of small bars,they will both have magnetic fields (or poles)focused on each end of the bars, one end oreinted“north” or “+”, and one end oreinted “south” or“-”. If I try to push the two north pole endstogether, they will repel and push away. If I tryto push the north pole end of one to the southpole end of the other, they will be attracted, jumptogether, and cling.

Magnets

likes repel

opposites attract

LESSON 2


2

<Thinking Activity

Suppose you have a balloon that has been blown up. Suppose yourub the balloon on a wool sweater. What will happen to the balloonif you release it?

Answer: The balloon will cling to the sweater. When the balloonand sweater rub together, each one gains a different electriccharge. The type of material the balloon is made of tendsto become negatively charged. The sweater becomespositively charged when it is rubbed against the balloon.Since opposites attract, particles in the balloon and sweaterpull toward each other.

negative charge

positive charge

Missing chargemakes the sweater

positive.

Borrowed chargemakes balloonnegative.

before rubbing after rubbing

Source: The Usborne Book of Science Experiments

LESSON 2


2

<Thinking Activity

Suppose you tie two inflated balloons together with a string. Thenyou rub the two balloons with a piece of wool fabric. You knowfrom the last activity that the balloons will become negativelycharged. When you hold the balloons by the middle of the string,what do you think will happen?

Answer: The balloons will push apart if they lose enough of theirpositive charge in the piece of wool.


LESSON 2


2

<Thinking Activity

Suppose you could see the electrical charges in a thunder cloud.

The negative charge in the bottom of the cloud causes a positivecharge in the ground underneath the cloud. Remember, oppositesattract. What do you think happens when you see a lightningbolt?

Answer: The cloud discharges a powerful amount of static electricityas the negative electrons pull toward the positively chargedground.

positive chargeat top

ground

negative charge


LESSON 2


2Now we can use this principle to begin to

understand electricity and current flow.

Current

Current is the flow of electrons from one pointto another. Electrons flow from a negative pointto a positive point. Current flow is measured inamperes. This is commonly abbreviated as amps.

Voltage

Voltage is the power in an electrical circuit.The voltage provides the “pressure” to push theelectrons through the circuit. The higher thevoltage, the greater the capacity for pushingelectrons; therefore, the greater the capacity forcreating current.

Another term used to describe voltage isvoltage potential. This is used to describe theamount of voltage available for an electricalcomponent or appliance.

LESSON 2


2EXERCISE – ELECTRICAL TERMS

Instructions: Match the words in the left column with an electrical meaningon the right side of the page. Place the letter corresponding to thecorrect definition in the blank beside each word.

____ 1. AC a. powerful static electricity

____ 2. amperes (amps) b. measure of cycles per second

____ 3. current c. electrically charged parts ofmatter

____ 4. DC d. flow of electrons from onepoint to another

____ 5. electrons e. measure of the pressure thatpushes electrons through acircuit

____ 6. hertz f. measure of current flow

____ 7. lightning g. type of electricity thatpulsates

____ 8. voltage h. common type of electricitysupplied by batteries

LESSON 2



g. 1. AC type of electricity that pulsates

f. 2. amperes (amps) measure of current flow

d. 3. current flow of electrons from one pointto another

h. 4. DC common type of electricitysupplied by batteries

c. 5. electrons electrically charged parts ofmatter

b. 6. hertz measure of cycles per second

a. 7. lightning powerful static electricity

e. 8. voltage measure of the pressure thatpushes electrons through acircuit

LESSON 2


2EXERCISE – ELECTRICAL FIELDS

Instructions: Think about the magnetic fields created by magnets. Select theletter that represents the most likely reaction of electrical fieldswith the indicated charges.

1. and

a. The magnetic forces will push away.b. The magnetic forces will pull together.

2. and


3. and


4.


+ +

+ –

– –

LESSON 2



1. and

Answer: a. The magnetic forces will push away.Likes repel.

2. and

Answer: b. The magnetic forces will pull together.Opposites attract.

3. and

Answer: a. The magnetic forces will push away.

4.

Answer: b. The magnetic forces will pull together.

+ +

+ –

– –

LESSON 2


2DIRECT-CURRENT ELECTRICITY

The fundamental principles for AC and DCare the same. We are going to start our discoverywith a closer look at DC.

As we discussed earlier, a primary source forDC is the battery. Batteries are made in manydifferent sizes, shapes, and voltages. Properbattery use is determined by the application.Obviously, the battery that makes your watchrun won’t start your car.

Batteries are made by placing two differentchemically-active elements called electrodes ina chemical. The chemical reaction that occurscreates a positive electron charge on one of theelectrodes and a negative charge on the other.

Battery

Does this ring a bell from our earlier discussion?

negativeelectrode

positiveelectrode

+chemical

Charging my battery

LESSON 3


2We already know that in electricity, opposites

attract. If we connect the negative and positiveelectrodes together through a conductor, theelectrons at the negative electrode will beattracted to the positive electrode, and electronswill flow through the conductor. We now havean electrical current flow.

Battery

+

conductor

current flow

positive

negative

LESSON 3


2Conductors and Insulators

Let’s have a quick review of conductors andinsulators. All matter is made up of atoms thatcontain electrons (along with protons andneutrons) Electrons have a negative charge. Freeelectrons are ones that move around freely inmatter.

In electrical terms, a conductor is matter witha large number of free electrons. An insulator ismatter with few free electrons. Metals areexcellent conductors. Copper is one of the bestand is the most common conductor used forelectricity. Rubber, plastic, and glass makeexcellent insulators because they have few freeelectrons.

In electricity, insulators are used to make surethat electricity goes in the direction we want.Also, insulation provides a significant safetybenefit. All exposed electrical wires should becovered by insulation to avoid electrical shorts,shock, or injury.

LESSON 3


2Resistance, Loads, and Circuits

Batteries have an electrical charge, but thecharge is temporary. Eventually, the battery willlose its charge and will become “dead.” Somebatteries are rechargeable and can be used manytimes.

If we connect a wire conductor directly fromthe negative terminal to the positive terminalwith no load in-between, we have created a directelectrical “short.” The wire conductor willbecome hot as a result of the maximum amountof current flow. This battery will quickly beexhausted, and worst of all, we have notaccomplished any work output.

A circuit is a complete path for electricalcurrent flow. The wire conductor that begins atthe negative element and returns to the positiveelement forms an electrical circuit.

In order to perform work, one or more loads

LESSON 3


2must be included in the circuit. The load can beone of a variety of electrical appliances such as alightbulb, motor, or portable radio. The energyfrom electricity is converted to other forms ofenergy. In the case of the lightbulb, the energyis converted to light. The motor converts theenergy to mechanical energy, and the radioconverts it to sound energy.

The load adds resistance to the circuit. Thismeans the electrons do not flow freely since thework they must do slows the flow. The amountof current flow in a circuit is inverselyproportional to the amount of resistance. As theresistance is increased, the current flow goesdown. If the resistance is increased to the levelof an insulator, there will be no current flow.

<

+

–

+

–

+

–

fanmotor

speakerradio

lightbulb

LESSON 3


2The length and size of the wiring in the circuit

also directly affects the resistance. The longerthe wire between the positive and the negativeterminals, the greater the resistance.

The larger the size or diameter of the wire, theless the resistance.

As the electrons force their way throughresistance, electrical energy is converted to heat.If this resistance was not a planned load of thecircuit, this energy is lost and the circuit isinefficient.

For your information, engineers usecomponents called resistors to control electricalflow. As they are designing circuits for electronicdevices, they place a specific resistance at theplace they want to control voltage and current.In the manufacturing process, the resistors aremade to the exact specifications of the engineerto provide an efficient and reliable appliance.

#12 gauge wireLESS RESISTANCE

#20 gauge wireMORE RESISTANCE

20 ft wireMORE RESISTANCE

10 ft wireLESS RESISTANCE

LESSON 3


2

<

<Thinking Activity

Though this example is not based on electricity, it might help youthink about the concept of resistance.

Suppose you have water running through a garden hose. Whathappens to the water if you step on a section of the hose?

Answer: Less water will be able to move through the hose. Whenyou squeeze the hose, the water meets more resistance as thepassageway narrows. You can create so much resistance thatthe flow can be completely blocked.

Remember, a narrower passageway creates moreresistance … even with electricity.

Thinking Activity

Suppose you have #10 gauge wire and #16 gauge wire. Whichone has the larger diameter?

Answer: The #10 gauge wire has the larger diameter of the two. Ifyou remember from earlier examples, #12 gauge wire visiblywas larger than #20 gauge wire. As the gauge numberincreases, the diameter of wire decreases.

Why would you choose to use the wire with a larger diameterover the other wire?

Answer: The larger the diameter, the less resistance the wire willcause.

LESSON 3


2Switches, Fuses, and CircuitBreakers

Switches allow us to control the flow ofelectricity in a circuit. A switch is a simple devicethat lets us turn an appliance on or off. Theportion of the switch we touch is made of aninsulator, so we will be protected from electricalshock. The inside of the switch contains electricalcontacts that transfer position when we activatethe switch.

Switches are designed as normally-open ornormally-closed switches. They operate just astheir names imply. In its normal position, anormally-open switch does not complete thecircuit, and no current can flow. When activated,the switch closes the circuit, and current isallowed to flow. A normally-closed switch, inits normal position, completes the circuit so thatthe current flows. When it is activated, the circuitis open, and no current can flow.

The most common manual switch is a toggleswitch.

normally-open switch normally-closed switch

ON

OFF

Toggle Switch

LESSON 3


2The ordinary light switch is an example of a

normally-open switch, and an emergency power-off switch is an example of a normally-closedswitch.

Fuses and circuit breakers serve the samepurpose. They provide for your personal safetyand protect electrical circuits from overloads.They can also be considered a type of switch.Fuses contain a metal element that is rated forthe voltage and current of a circuit. As a currentincreases through the fuse, the metal elementheats up. If the current exceeds the rating of thefuse, the metal element melt, separate and breakthe connection. and the circuit will be opened.Current flow will stop because there is no pathfor flow.

The circuit breaker works in much the sameway. As current increases, the element in thecircuit breaker heats up. When the currentexceeds the limits of the circuit breaker, thebreaker is designed to mechanically trip to the“off ” position. This creates an open circuit, andthe current stops flowing.

Blown fuses must be replaced while circuitbreakers can be reset to the “on” position.

LESSON 3


2ELECTRICITY CAN KILL!

It is extremely important to use properprecautions and practices when dealing withelectricity. While the normal flashlight batterywill not hurt you, a car battery can give you anelectrical burn, and 120-volts AC in the homecan kill.

Always ensure power is removed from acircuit before replacing a fuse. If a fuse or circuitbreaker continues to indicate a problem, do notreplace them with ones with a higher rating. Thisdefeats their purpose of protection. Try to locatethe source of the overload. If you are notqualified, call a professional.

Excessive current will not only damageelectrical appliances, serious safety concerns maydevelop. Excessive current means excessive heat.Insulators can melt from heat resulting in thepotential for electrical shock. Excessive heat fromelectrical circuits or appliances is also the causeof many fires.

My message is simple … let fuses and circuitbreakers do their jobs!

LESSON 3


2Practical Circuits

Let’s discuss batteries a little more. Commonhousehold batteries come in many sizes such asAA, AAA, C, and D. Each of these batteriesprovide 1.5 volts DC. The larger batteries havea greater reserve of energy.

Batteries can be connected together toprovide higher voltage and current capabilities.When connecting batteries, the negativeterminal of one battery must be connected tothe positive terminal of another. Whenconnected in this manner, the voltage of eachbattery in the string is added to determine thetotal available voltage.

Batteries

1.5 v 3.0 v

6.0 v

1.5

v

1.5

v

1.5

v

1.5

v

1.5

v

1.5

v

1.5

v

LESSON 3


2A flashlight is a good example of this type of

circuit. There is a power source (the batteries), aload (bulb), a circuit control (switch), andconductors. Let’s take a look.

1.5 v

1.5 v

1.5 v

1.5 v–

+

–

+

–

+

–

+

conductor

switch

load (bulb)

Flashlight

LESSON 3


2

<

Thinking Activity

In this example of the flashlight, what is the total voltage appliedto the bulb?

Answer: The total voltage is 1.5 (volts) × 4 (batteries) = 6 v.

Is the switch normally-open or normally-closed?

Answer: The switch is normally-open.

What would happen if the conductor did not make electricalcontact with the negative end of the battery string?

Answer: Without electrical contact, you would not have a circuitfor the current to flow and the bulb would not light.

1.5 v

1.5 v

1.5 v

1.5 v–

+

–

+

–

+

–

+

conductor

switch

load (bulb)

LESSON 3


2Let’s look at another principle of voltage and

current. We said earlier that current is directlyproportional to the voltage and the resistance.In our flashlight example, there is only one load/resistance, which is the bulb. In this case, theentire 6 volts is placed across the bulb. Thefilament of the bulb glows brightly.

Series Circuits

Refer to the figure below where a flashlighthas two identical bulbs.

switch

1.5 v

1.5 v

1.5 v

1.5 v–

+

–

+

–

+

–

+

conductor

load (bulbs)

Flashlight

LESSON 3


2We are now looking at a series circuit. A series

circuit has one or more loads included in a single-circuit loop from the power source. In a seriescircuit, there is only one path for current flow.The voltage is divided among the different loadsin this circuit.

In our previous flashlight example with onebulb, the entire 6 volts were applied to the bulb.In this example, with two identical bulbs, theavailable voltage will be equally divided acrosseach bulb. Each bulb will feel 3 volts. As weindicated earlier, we have increased the resistanceby adding the additional bulb; so, we havedecreased the current flow. As you can logicallysee, the reduced voltage and current will resultin less light coming from each individual bulbas compared to a single bulb in the circuit.

A little later we will discuss parallel circuits;however, this is a good time to begin tounderstand the relationship between voltage,current, and resistance. This relationship isdescribed by Ohm’s law.

LESSON 3


2Ohm’s Law

Ohm’s law is a simple formula used todescribe the relationship between current,voltage, and resistance. Because voltage mustpush the current through the resistance, a changein any of the three will result in a change to theothers.

• Voltage is the energy supplied to the charge;power is the product of current and voltage.In Ohm’s law, the voltage is represented bythe letter E.

• Current is measured in amps, and in Ohm’slaw, is represented by the letter I.

• Resistance is measured in ohms, and in Ohm’slaw, is represented by the letter R.

It’s really simple. Let’s get started!

Ohm’s law states that one volt pushingthrough one ohm of resistance will result in oneamp of current. Two volts pushing through oneohm of resistance will result in two amps ofcurrent.

Stated in math terms, this would be:

current = voltage ÷ resistanceor

amps = volts ÷ ohmsor

I = E/R

LESSON 3


2Let’s look at some examples:

An increase in voltage will cause an increasein electrical current flow. An increase in circuitresistance will cause a decrease in electricalcurrent flow.

Using Ohm’s law, you can calculate either thevoltage, current, or resistance in a circuit if youknow the value of the other two components.

LESSON 3

6 volts resistor3 ohmsbattery power

supply

current flow = 2 amps6 volts ÷ 3 ohms = 2 amps

+

–

12 volts resistor3 ohmsbattery

powersupply

current flow = 4 amps12 volts ÷ 3 ohms = 4 amps

+

–

12 volts resistor24 ohmsbattery power

supply

current flow = .5 amp12 volts ÷ 24 ohms = .5 amp

+

–

Example 1:

Example 2:

Example 3:


2Here are some more examples.

voltage = current × resistanceor

volts = amps × ohmsor

E = I × R

resistance = voltage ÷ currentor

ohms = volts ÷ ampsor

R = E/I

? volts resistor10 ohms

battery powersupply

voltage = 6 volts.6 amp × 10 ohms = 6 volts

? volts resistor20 ohms

battery powersupply

voltage = 12 volts.6 amp × 20 ohms = 12 volts

.6 amp .6 amp

+

–

+

–

12 volts resistor? ohms

battery powersupply

resistance = 12 ohms12 volts ÷ 1 amp = 12 ohms

12 volts resistor? ohms

battery powersupply

resistance = 40 ohms12 volts ÷ .3 amp = 40 ohms

1 amp .3 amp

+

–

+

–

LESSON 3


2Parallel Circuits

Earlier we discussed series circuits thatprovide only one path for current flow. We alsolooked at the example of the flashlight with twobulbs. Remember how both bulbs lit? However,since they were sharing the voltage, they weremore dimly lit.

In many applications, it is not desirable tohave a loss of output energy when multiple loadsshare a circuit. The parallel circuit solves thisproblem. A parallel circuit is one that providesmore than one path for current flow. In a parallelcircuit, the total input voltage is applied acrosseach section or “leg” of the circuit.

Let’s look at some examples:

Since points C and D are directly connected to points A and B bygood conductors, the full voltage potential of 6 volts is felt atpoints C and D. The bulb has the entire 6 volts applied to it.

A

B

C

D

LT1

series circuit

6 volts

+

–

LESSON 3


2

In this parallel circuit, points E and F are electrically the same aspoints C and D. The entire 6-volt pressure is felt across both bulbs,LT1 and LT2. Each will burn as brightly as the single bulb in theseries circuit.

In this example, we have added a third leg. The entire 6 volts willbe felt by all three bulbs. Each will glow as brightly as the 2 bulbsin the previous example.

Ohm’s law also applies to each leg of the circuit. The voltage appliedat each leg, along with the resistance in that leg, will determinethe amount of current flow through that leg.

A

B

C

D

LT1 LT2

parallel circuit

6 volts

E

F

+

–

LT3

G

H

A

B

C

D

LT1 LT2

parallel circuit

6 volts

E

F

+

–

LESSON 3


2

A B

6 volts3 ohms 3 ohms

current flow at point A = 2 amps6 volts ÷ 3 ohms = 2 amps

current flow at point B = 2 amps6 volts ÷ 3 ohms = 2 amps

+

–

A B

12 volts4 ohms 24 ohms

current flow at point A = 3 amps12 volts ÷ 4 ohms = 3 amps

current flow at point B = .5 amp12 volts ÷ 24 ohms = .5 amp

+

–

LESSON 3


2In a parallel circuit, the total current in the entire circuit will equalthe sum of all the individual leg currents. Look at the previousexample.

Now I want to discuss the application ofOhm’s law in parallel circuits. It is not importantthat you master this area, but I want you to beaware of the key concepts.

First, let’s review the current in a parallelcircuit. The current passing through each leg isadded to the current in the other legs todetermine the total circuit current.

B

A

C

12 volts4 ohms

24 ohms

current flow at point B = 3 amps

current flow at point C = .5 amp

point A will have the entirecircuit current of 3.5 amps

3 amps (B) + .5 amp (C) = 3.5 amps (A)

+

–

LESSON 3


2

The current through R1 = 3 amps. (12 volts ÷ 4 ohms = 3 amps)The current through R2 =12 amps. (12 volts ÷ 1 ohm = 12 amps)The current through R3 = 6 amps. (12 volts ÷ 2 ohms = 6 amps)

21 amps

The total circuit current read at Point A is 21amps.

To determine the total resistance (RT) of thecircuit, we use Ohm’s law. Remember, resistanceequals voltage divided by current.

This low level of resistance may surprise you!Let’s double check our calculation. The formulafor determining the total resistance in a parallelcircuit is:

12 volts 4 ohms 1 ohm

+

–

2 ohmsR1 R2 R3

A

LESSON 3

R =

E

I

RT =

12

21

RT = .57 ohms

1

RT

=1

R1+

1

R2+

1

R3


2We substitute the known values and we now

have:

Hey, Ohm’s law still works! You may notremember the formula, but there are two keypoints to remember.

1. The total current in a parallel circuit is read at the power supplyoutput.

2. The total resistance in a parallel circuit will be equal to or lessthan the smallest resistance in any individual leg. In ourexample, R2 is the smallest resistor; we know that the totalresistance will be 1 ohm or less.

LESSON 3


2You can see how the use of parallel circuits

increases current capacity for a power source.Engineers are careful in designing parallel circuitsto not overload the power source or conductorswith excessive current.

Parallel circuits are very beneficial ineffectively using electrical energy. You will seegreat examples of this as we go into AC andhousehold current.

There are additional important points for youto remember:

• While the principles for AC and DC are basically the same, manydevices will not operate correctly if attached to the wrong powersource. For example, motors and lightbulbs are engineered differentlyfor use with AC or DC circuits. Attaching to the wrong power sourcewill likely damage the electrical device. Always check a device closelyfor the proper power requirements.

• Polarity is a term used in reference to positive and negative electrodesor terminals. When attaching a power source to a circuit, properpolarity must be observed. This means the positive electrode of thebattery must be attached to the circuit at the positive entry point,and the negative electrode must be attached to the negative entrypoint. Reversing these connections will result in the device notworking properly, and damage to the device may occur.

LESSON 3


2EXERCISE – APPLICATIONS I

Instructions: Read about each workplace situation. Then select the letter thatrepresents the best answer to each question.

1. Cords and More produces electrical cords for computers.They are having trouble receiving materials from theirsupplier. Currently, the coating on the cords is made ofrubber. A work team is considering other options for thecoating. Which of the following suggestions should beconsidered?

a. Use a coating made of copper.b. Use a coating made of cotton fabric.c. Use a coating made of plastic.d. Eliminate the coating.

2. Glenn is working as an apprentice for an electrician. Heknows that current flow is inversely proportional toresistance. His boss wants to decrease the resistance in acircuit that keeps overheating. She asks Glenn to get somewire from the truck. Which wire should Glenn get?

a. a lower gauge wireb. a higher gauge wirec. a wire that is the same gauge as currently used, but that

is shorterd. The wire will not affect the resistance.

LESSON 3


23. Jose is installing cabinets in the master bath of a home

under construction. His co-worker is working in the sameroom using an electric sander to finish some baseboards.All lights in the room are on while they work. When Joseuses his electric drill, both workers lose power. What iscausing this problem?

a. There is a short in the electric drill.b. There is a short in the electric sander.c. The lights are drawing too much current.d. The power supply at the service entrance is not adequate

to run the two appliances.

LESSON 3



1. Answer: c. Use a coating made of plastic.The rubber coating is an insulator that keepselectrical current from escaping the cord. In additionto rubber, plastic and glass are good insulators.

2. Answer: a. a lower gauge wireRemember, the size of wire increases as the gaugenumber of the wire decreases, so lower gaugemeans larger wire. Larger wire has less resistancethan wire that has a smaller diameter.

3. Answer: a. There is a short in the electric drill.The power stops when Jose uses the drill. A shortin the drill would cause the breaker to trip. This stopsthe power to the circuit.

LESSON 3


2EXERCISE – USING OHM’S LAW

Instructions: Use the following diagrams to calculate the answer to eachquestion. Select the letter that represents your answer.

1. How much current is in this circuit?

a. 6 ampsb. 24 ampsc. 3 ampsd. 4 amps

2. How much resistance is in this circuit?

a. 24 ohmsb. 12 ohmsc. 6 ohmsd. 24 volts

12 volts? amps

resistor2 ohms

battery powersupply

+

–

12 volts2 amps

resistor? ohms

battery powersupply

+

–

LESSON 3


23. How many amps are in this circuit?

a. 360 ampsb. 36 ampsc. 2.5 ampsd. .4 amp

4. How much voltage is powering this circuit?

a. 6 voltsb. 15 voltsc. .2 voltd. 1.5 volts

12 volts? amps

resistor30 ohms

battery powersupply

+

–

? volts.5 amp

resistor3 ohms

battery powersupply

+

–

LESSON 3


25. How many ohms of total resistance are in this circuit?

a. 35 ohmsb. 20 ohmsc. 10 ohmsd. 5 ohms or less

6. What is the current flow at Point B in this circuit?

a. .5 ampb. .25 ampc. 24 ampsd. .43 amp

12 volts20 ohms 10 ohms+

–

5 ohms

LESSON 3

A B

6 volts2 ohms 12 ohms+

–



1. Answer: a. 6 amps12 volts ÷ 2 ohms = 6 amps

2. Answer: c. 6 ohms12 volts ÷ 2 amps = 6 ohms

3. Answer: d. .4 amp12 volts ÷ 30 ohms = .4 amp

4. Answer: d. 1.5 volts.5 amp × 3 ohms = 1.5 volts

5. Answer: d. 5 ohms or less

6. Answer: a. .5 ampCurrent flow at Point B = .5 amp6 volts ÷ 12 ohms = .5 amp

LESSON 3


2EXERCISE – CALCULATING VOLTAGE

Instructions: Use the following diagram to determine the answer to eachquestion. Select the letter that represents your answer.

1. How much total voltage is available on this battery-poweredcircuit?

a. 1.5 voltsb. 4.5 voltsc. 3 voltsd. no voltage

2. How much total voltage is available on this battery-poweredcircuit?

a. 1.5 voltsb. 3 voltsc. 6 voltsd. no voltage

? v

1.5

v

1.5

v

1.5

v––– +++

? v

1.5

v 1.5

v

–++–

LESSON 3


23. How much total voltage is available in this remote control?

a. 1.5 voltsb. 3 voltsc. 6 voltsd. no voltage

4. What is the voltage between Points B and D in this parallelcircuit?

a. 12 voltsb. 6 voltsc. 4 voltsd. 3 volts

1.5

v –+

1.5

v– +

INFR

AR

ED

RE

MO

TE

CO

NT

RO

L U

NIT

IRC

UA

C

LT1 LT212 volts

B

D

+

–

LESSON 3


25. What is the voltage felt at LT2 in this series circuit with

identical bulbs?

a. 12 voltsb. 6 voltsc. 3 voltsd. 2 volts

6 voltsLT1 LT2+

–

LESSON 3



1. Answer: b. 4.5 voltsThe voltage of each battery in a string is addedtogether to find the total voltage.1.5 + 1.5 + 1.5 = 4.5 volts

2. Answer: d. no voltageThe second battery position stops the electron flow.Two positive terminals repel when in contact.

3. Answer: b. 3 volts1.5 + 1.5 = 3 volts

4. Answer: a. 12 voltsIn a parallel circuit, the entire 12 volts of pressureis felt by both bulbs.

5. Answer: c. 3 voltsIn a series circuit, the voltage is divided equallyamong loads since the bulbs are the same.

LESSON 3


2ALTERNATING-CURRENTELECTRICITY

Alternating current (AC) is the normal powersource for our homes. It is also used for poweringlarge buildings and industrial applications. ACis developed by generators. The generators thatprovide the power for our communities are verylarge. These generators are driven by the energyof water at hydroelectric facilities, by steamdeveloped from burning fossil fuels like coal, andby atomic energy. The electrical power isdistributed by large conductors to powersubstations and then on to our homes.

AC is the choice for general power usebecause it is much easier to send over longdistances and can be more easily controlled. Veryhigh voltages are sent to electrical substations.At the substations, the voltages are reduced byusing transformers. The lower voltage is then sentto your neighborhood where additionaltransformers are installed to further reduce thevoltage and directly supply your home.

Even in your house wiring, transformers areoften used. A small transformer is installed in a120-volt circuit to reduce it to a lower voltageto power your doorbell.

Electric current ischanged to a form ofpower for homes at

substations.

LESSON 4


2AC in the home is provided through a meter

and then to the power service entrance. Theservice entrance will also normally be your maincircuit breaker or fuse box. The incoming poweris provided by three large wires. Two of the wireswill be “hot” wires. The third wire is called theAC “neutral.” Each of the hot input lines carry120 volts AC 60 cps. The neutral, as the nameimplies, has no charge.

In most of our homes, we have therequirement for two levels of AC voltage. Themost common is 120 volts, which providespower for lights, TVs, hair dryers, refrigerators,and other small appliances. These are parallelcircuits and are created by using one of the hotinputs and the neutral. Other large appliancessuch as clothes dryers, electric ranges, hot-waterheaters, and air conditioners require a highervoltage. These appliances are normally placedin a series circuit by themselves and operate on240 volts.

LESSON 4


2

Let’s step back a minute and clear up a coupleof points. Houses wired before the 1940s mayhave only 120 volts AC available. Also, we haveall heard of appliances that operate on 110 voltsAC and ones that operate on 220 volts AC. Weare talking about the same thing! Early on, 110volts and 220 volts were the commondescriptions. In fact, the power companies wereproviding higher power than that to compensatefor power and load variations. The target inputis 120 volts on each hot line. During a singleday, this may vary between 115 volts and 125volts. Today, appliances are being labeled at 120volts and 240 volts to more accurately reflecttheir operation.

service entrance

LESSON 4


2Theory of Operation

You do not need to know all of the electricaltheory about AC to be able to solve related,practical problems. I am going to give you just alittle to whet your appetite. More informationcan be found at your local library.

AC stands for alternating current. That meanscurrent will alternate in its direction of flow. Let’stake 120 volts AC 60 cps first. We know thereare 120 volts of potential, and it cycles 60 timesper second. Refer to the following illustration.

Figure 1

In Figure 1, we have one full cycle. A cycle isalso called a sine wave. Through the center ofthe cycle, we have drawn a “0” reference line.

hot input

positive(+)

negative(–)

0 (zero) reference

LESSON 4


2

Figure 2

When the cycle is above the reference line, itis positive. When it is below the reference line,it is negative. Now we attach the “hot” cyclingline and the AC neutral line to a load andcomplete the circuit. Notice in Figure 2, whenthe cycle is on the positive side of the reference,the current will flow in one direction. When thecycle moves to the negative side of the reference,the current alternates and flows in the oppositedirection. Remember, the current will alternate60 times per second.

hot input

positive (+)

negative (–)

120 vLOAD

currentflowing

current flowalternates (reverses)

AC neutral

hot 120v

LESSON 4


2Now let’s look at 240 AC volts at 60 cps. For

240 volts, we do not use the AC neutral. We usethe 2 hot AC inputs. Each input carries 120 volts,and we are effectively going to add them togetherto attain the 240 volts. Both of the hot inputsare cycling the same as we described in 120 volts.Refer to the following illustrations in Figures 3and 4.

Figure 3 Figure 4

In Figure 3, each of the inputs are cyclingpositive and negative to the reference line. Noticethat they are not cycling in the same phase. Whilethe input for line A is at its most positive point,the input for line B is at its most negative point.In Figure 4, when input A is at its positive pointand input B is at its negative point, we will haveadded the two voltages, and the current will flowin one direction. When the cycles continue, thevoltages will still be added; however, the currentflow will be in the alternate direction. Remember,the inputs will cycle 60 times each second. Byconnecting the hot input A and the hot input Bto a load, we complete the circuit.

(+) (+)

2ndhot input

(–) (–)

hot input

(–) (–)

hot input

(+)

(–)

(+)

(–)

hot input

(+) (+) (+)

(–)

(+)

(–)

240vLOAD

LINE A

LINE A

LINE B

LINE B

A and B are added

LESSON 4


2Again, this theory is to give you only a general

idea of alternating current and the difference inwiring for 120-volt and 240-volt circuits. A goodphysics book can take you a lot further!

When dealing with household appliances andwiring in the home, three wires are used for 120volts. One hot wire (normally with blackinsulation), one AC neutral wire (normally withwhite insulation), and one ground wire(normally with green insulation or uninsulatedcopper wire).

For 240 volts, three wires are also used. Ahot wire (normally with black insulation), asecond hot wire (normally with red insulation),and a ground wire (normally with greeninsulation or uninsulated copper wire).

Power outlets and plugs are different to avoidaccidently plugging an appliance to the wrongvoltage. The 240-volt plugs and power outletswill be larger, and the arrangement of the prongswill be different.

120 v 240 v

Power Outlets

LESSON 4


2We will discuss the purpose of the ground

wire later in this lesson.

Household Circuits

Let’s take a closer look at household circuits.The AC power comes into your house and isattached at the service entrance. It then passesthrough the main circuit breaker and isdistributed to smaller circuit breakers in thepanel. Each of the smaller circuit breakers willprovide overload protection for a specific circuit.A house wiring plan is developed to keep fromattempting to drive too many appliances on onecircuit. A typical 120-volt circuit will be designedto not exceed 20 amps.

A typical layout will have the lights and wallplugs for one or more rooms on the same circuit.(See Figure 5.) The refrigerator may be on acircuit by itself since it requires more current.The circuit breakers for 240 volts will occupytwo positions in the panel box since they areusing both hot inputs.

LESSON 4


2Typical Service Box Layout

and Circuit Description

Figure 5

Notice the double breakers providing 240 volts of power to the range, dryer,and air conditioner.

main breaker

1 2

3 4

5 6

7 8

9 10

11

LESSON 4


2Grounding Electrical Circuits

At the building service entrance, the ACneutral line provides the second leg for currentflow for 120-volt circuits. It is also connected toa ground. (See Figure 6.) Where possible, ametal, cold-water pipe that runs undergroundis found and connected to the AC neutral at theservice entrance. This provides a true “earthground” and is very important for safety!

Figure 6

NOTE: Circuit breakers should always be placed on the hot side to interruptthe supply voltage.

A breaker on the neutral side is ineffective as the hot leg will stillbe active in the circuit even with the breaker tripped.

mainbreaker

cold water pipe or electrode ground

hot bus barsindividual circuit breakersclamp on hot bus bars

neutral bus bar

service entrance

LESSON 4


2Electrical Codes

Safety is a primary consideration in theinstallation and repair of electrical circuits. TheNational Electrical Code® (NEC) establishes theminimum requirements for electricalinstallations. This includes materials andprocedures to be used. These are the minimumstandards. More rigid requirements may be setby individual states, counties, and/ormunicipalities. It is important that local codesbe followed, and the proper permits are obtainedbefore beginning a project.

LESSON 4


2Typical Circuits

Now let’s take a look at some typicalhousehold circuits. Do you remember the seriesand parallel circuits that we studied in DC?They’re back!

We will start simple. Figure 7 shows a seriescircuit powered by 120 volts AC with a lightand a switch in the circuit. Because the switch isopen, the circuit is not complete and the lightwill not burn.

In Figure 8, the switch is closed. This allowscurrent to flow and the bulb burns.

Figure 7 Figure 8

120 v

neutral

sw1120 v

neutral

sw1

LESSON 4


2Now let’s look at a parallel light circuit. In

Figure 9, we have three lights in a parallel circuitwith a switch. Since the switch is closed, all threebulbs burn equally bright.

Parallel Circuit

Figure 9

NOTE: In electrical circuit diagrams, wires having electrical connectionare drawn as or .

Wires not having electrical connection are drawn as .

In the previous illustration, the neutralwiring is shown crossing over the hot wire.However, there is no electrical contact.

120 v

neutral

sw1

LESSON 4


2

Figure 10

In this typical circuit, we have 4 wall outletswired in parallel. (See Figure 10.) All will haveactive power available at the outlet.

Sometimes it is desirable to control walloutlets by a switch. We have redrawn theprevious circuit and added points A, B, and Cfor you to try the following Thinking Activity.

120 v

neutral

1 2 3 4

circuitbreaker

LESSON 4


2

<

Thinking Activity

What will happen if a switch is installed at point A and is turnedoff?Answer: A switch turned off at point A will remove the voltage

from all 4 wall plugs. None will have power.

What will happen if a switch is installed at point B and is turnedoff?Answer: A switch turned off at point B will remove the voltage

from wall plug 2. Wall plugs 1, 3, and 4 will have power.

What will happen if a switch is installed at point C and is turnedoff?Answer: A switch turned off at point C will remove the voltage

from both wall plugs 3 and 4. Wall plugs 1 and 2 willhave power.

120 v

neutral

1 2 3 4

circuitbreaker

A B C

LESSON 4


2Three-way switches are specially-designed

switches used to control appliances from morethan one location. Hallway lights are a commonapplication. A light can be turned on from eitherof two switches located at opposite ends of thehallway.

Figure 11

• In the switch position as drawn in Figure 11,there is no path for current, so the light isoff.

• Transferring sw1 to the up position willcomplete the circuit, and the light turns on.

• Transferring sw2 to the down position willalso complete the circuit and turn on thelight.

• Either switch can also open the circuit andturn the light off.

We have drawn the switches close togetherfor illustration purposes. They could be locatedat the opposite ends of a hallway.

sw1

sw2

120 v

neutral

LESSON 4


2Grounding isImportant for Safety!

House wiring contains a ground wire thatshould be used to ground fixtures, appliances,and electrical outlets.

Let’s discuss why the ground is so important.Let’s assume you have an ungroundeddishwasher. The hot AC line becomes frayed andtouches the metal chassis (the case of thedishwasher). The metal case now has 120 voltspotential on it and is looking for a circuit path.If you touch the case, you could experience apowerful electrical shock by providing a circuitthrough your body! One hand on the washerand one hand on the water faucet and ZAP! Youcan even complete a circuit through your feetdepending on the material in your shoes andthe surface you are standing on.

concrete

LESSON 4


2In the same example, if the case is grounded,

the frayed wire touches the case and immediatelyhas a direct path to ground for a complete circuit.This direct path immediately overloads thecircuit and trips the circuit breaker or blows afuse. The shock potential has been removed andthe malfunction repaired.

Many plug-in appliances have the same safetyfeature. The third prong on the plug, normallyround, grounds the case of the appliance toground at the outlet.

Some two-prong plugs accomplish a similareffect by having one of the prongs larger thanthe other. This allows the plug to be insertedinto the power outlet in only one way. Thisassures the case of the appliance is tied to theAC neutral side and will trip the circuit breakeror fuse if a short occurs.

WARNING!

LESSON 4


2Ground FaultCircuit Interruption (GFCI)

GFCIs are another type of circuit breaker thatis used in potentially hazardous locations.Electrical codes now require they be installed incircuits for bathrooms, outside plugs, andgarages. These are considered hazardous becauseof the nearness to water, water pipes, and otherpotential grounds, which could result in shock.

GFCIs detect very small voltage leaks thatwill not normally affect a regular circuit breaker.Detection of a small leak will trip the breakerand remove power from the circuit. GFCIs arecommonly built directly into power outlets andcan be reset at the outlet.

GFCI

LESSON 4


2EXERCISE – APPLICATIONS II

Instructions: Read about each workplace situation. Then select the letter thatrepresents the best answer to each question.

1. John is replacing a heating and air conditioning thermostat.The power at the thermostat is low voltage. What devicewas used to lower the voltage?

a. a resistorb. a transformerc. an insulatord. a circuit breaker

2. The window air conditioner in the office at Frank’sInsurance is not working properly. Ramon has been askedto identify the problem. Most of the time it cools the office.However, when the light over the counter is turned on, theair conditioner trips the circuit breaker. What should Ramondo first?

a. Check to see that the air conditioner is plugged into thewall outlet.

b. Use a meter to read ohms to see if the air conditioner isreceiving 120 volts of power.

c. Check to see if the air conditioner is on the same circuitas the light.

d. Take the bulb out of the light over the counter.

LESSON 4


23. Amy is in the bathroom getting ready to dry her hair. When

she turns the hair dryer on, it does not work. What shouldAmy try first?

a. Reset the GFCI in the bathroom outlet.b. Buy another hair dryer.c. Go to an outlet in another room.d. Use a fan to dry her hair.

4. Kelly is installing a circuit breaker at the distribution panelof a home. In which portion of the circuit should the circuitbreaker be installed?

a. on the green wireb. on the black wirec. on the white wired. It does not matter which wire Kelly uses.

5. Doug goes into the storage room to get some hardware todo a job. While he is looking through the bins for deckscrews, one of the overhead lights goes out. There is notenough light to see in the bins. He should most likely:

a. check the fuse box.b. replace the lightbulb.c. call an electrician.d. try to do the job without the deck screws.

LESSON 4


26. Pam and David were in charge of Christmas decorations

for the company store window. They had to buy 2 new setsof lights to add to the old collection to decorate the treeand outline the window. Pam noticed that when one lightin an old set went out, the entire string went out. If a lightwent out in the new set, the rest of the string still burned.What allows the new string to continue to burn?

a. The lights are on a series circuit.b. The lights are on a parallel circuit.c. The lights receive more current than the old sets.d. The bulbs do not create a load for the circuit.

LESSON 4


27. There are 12 outlets on a parallel circuit in the Easy Chairs

for Easy Living showroom. Nick moved a lighted lamp thatwas plugged into outlet 2. He moved it near outlet 8. Whenhe plugged the lamp into this outlet, it did not work. Nick iscorrect to think that most likely:

a. outlets 8 - 12 will not work.b. all outlets except for outlet 2 will not work.c. there is a malfunction in outlet 8.d. the circuit breaker has been tripped.

LESSON 4


28. Look at the following diagram. Which statement is true?

a. Switch 1 is closed, and switch 2 is open.b. Switch 1 is open, and switch 2 is closed.c. Switch 1 and switch 2 are open.d. Switch 1 and switch 2 are closed.

sw1

sw2

120 v

neutral

LESSON 4



1. Answer: b. a transformer

2. Answer: c. Look in the service box to see if the airconditioner is on a single circuit.

3. Answer: a. Reset the GFCI in the bathroom outlet.

4. Answer: b. on the black wire

5. Answer: b. replace the lightbulb.

6. Answer: b. The lights are on a parallel circuit.

LESSON 4


27. Answer: c. there is a malfunction in outlet 8.

8. Answer: d. Switch 1 and switch 2 are closed.

sw1

sw2

120 v

neutral


2Well, that’s the last exercise on this level. It is

time for the Posttest. Remember, this will helpyou to know how much you understand aboutLevel 2. If you feel you are not ready, just goback and review the material first.

I will provide the answers so that you cancheck yourself at the end of the Posttest. Don’tbe tempted to look ahead!

If you don’t do well, you can go back, review,and retest yourself. I know you will do just fine.Good luck!

No peeking!

LESSON 5


2EXERCISE – POSTTEST

Instructions: Study the following diagram. Select the letter of the response thatbest answers each question.

1. You recently start working at Lewisburg Printing Company.They use a conveyor belt to move boxes of books from theproduction floor to the shipping dock. The belt is 30 feetlong and there is a 6-foot fall to the dock. What is themechanical advantage of using this plane?

a. 36 to 1b. 30 to 1c. 6 to 1d. 5 to 1

30 ft

6 ft

POSTTEST


22. You are planning to take your boss to the airport. When

you get into the car to go pick him up, your car will notstart. You determine the battery is dead. The most likelycause is:

a. a bad cell in the battery.b. poor battery connection.c. faulty battery charging system.d. excessive accessory use or an electrical short is draining

battery.e. Any of the above could be the cause.

3. You are working as a mechanic in a garage when you noticethat the lift is not working properly. After checking somegauges, you notice that the fluid pressure is low. Youshould:

a. run the machine on low fluid.b. call a repairperson to check the gauge.c. avoid using the lift.d. add fluid to the reservoir.

POSTTEST


24. On your way to work, you have a flat tire. You find a car jack

in the trunk of your car that looks like the one below. Whatbasic machine principle is used by the jack?

a. the inclined planeb. the leverc. the pulleyd. the screw

POSTTEST


25. You are on a job at work using the company vehicle when

you have a flat tire. You find a car jack in the trunk of thecompany vehicle that looks like the one below. What basicmachine principle is used by this jack?

a. the wedgeb. the leverc. the pulleyd. the screw

POSTTEST


26. After a long and frustrating day at work, you go to dinner

with your spouse in the family car. Not in a million yearswould you believe it could happen again! You have to call aservice truck to fix the flat because you do not have a sparetire. The jack used looks like the one below. What principlecauses the jack to lift your car?

a. fluid pressureb. inertiac. gravityd. condensation

POSTTEST


27. You start a new job at the Sound Factory that specializes

in quality stereo systems. When you crank up the volumeas high as it will go on one of the powerful systems, thewhole system shuts down. The most likely cause of theproblem is:

a. the circuit breaker for the power outlet tripped.b. the main circuit breaker for the building tripped.c. the stereo plug has a short in it.d. the fuse for the stereo system audio-output blew.

POSTTEST


28. Which one of the following parallel circuits shows Point A

as being “hot”?

a.

b.

c.

d.

120 v

neutral

sw1

point A

point A

120 v

neutral

sw1

120 v

neutral

sw1

120 v

neutral

sw1

point A

point A

POSTTEST


29. You are trying to determine how much resistance is in a

circuit. What device do you need to use?

a. an ohmmeterb. an ammeterc. a voltmeterd. a thermometer

10. You have been assigned to clean up litter on companyproperty, so you bring your battery-operated radio to thecleanup site. You put new batteries in it before you leavefor work. When you get to the site, you turn the radio on.The radio does not work. What should you do?

a. Check to see if the power cord is frayed.b. Replace the antenna.c. Check to see if the batteries are inserted correctly.d. Go home.

11. When you turn the faucet on at the bathroom sink, the waterbarely trickles out. What should you do?

a. Immediately call a plumber.b. Immediately call the water company.c. Check to see if there is water pressure at the bathtub

faucet.d. Attach a water-pressure gauge to the faucet.

POSTTEST


212. You want to reduce the current flow in a circuit. You should:

a. increase the voltage.b. add resistors to the circuit.c. remove the circuit breaker.d. remove the insulators.

13. How much current is in this circuit?

a. 3 ampsb. 12 ampsc. 6 ampsd. There is no current flow in this circuit.

6 volts? amps

resistor2 ohms

battery powersupply

+

–

POSTTEST


214. How much resistance is in this circuit?

a. 144 ohmsb. 12 ohmsc. 1 ohmd. There is no resistance is this circuit.

15. How much voltage is powering this circuit?

a. 24 voltsb. 1.5 voltsc. .67 voltsd. 64 volts

12 volts12 amps

battery powersupply

+

–

? volts6 amps

resistor4 ohms

battery powersupply

+

–

POSTTEST


216. You installed an over-the-counter microwave oven in a

kitchen in an older apartment complex. The customer callsyou to complain. If she touches the microwave while stirringa pot on the stove, she receives an electrical shock. Whatis the most likely solution to the problem?

a. Tell the customer to only use plastic spoons for stirring.b. Tell the customer to keep the microwave unplugged at

all times.c. Tell the customer to use glass cookware instead of metal.d. Make sure both the microwave and stove are properly

grounded.

17. There are 4 overhead lights in a hallway where you work.When one of the bulbs burns out, the other lights go outalso. What would explain this occurence?

a. The lightbulbs are different brands.b. The light sockets are on a series circuit.c. The light sockets are on a parallel circuit.d. Electrical current does not react consistently.

POSTTEST


218. You recently moved in a new house. You are experiencing

some electrical difficulty in the kitchen. When therefrigerator, dishwasher, and toaster are all on, the circuitbreaker trips. What is the most likely problem?

a. a defective circuit breakerb. The power usage exceeds the circuit-breaker capacity.c. a defective refrigeratord. a short at the wall power outlet

19. You just bought a new 240-volt window air conditioner. Younotice the plug is different from your old 120-volt airconditioner. What should you do?

a. Bend the new plug so that the prongs will fit.b. Swap the plugs on the air conditioners.c. Add an extension cord adapter.d. Have an electrician add a 240-volt circuit.

20. Before working with electrical wires, which of the followingsafety precautions should be taken?

a. Turn the circuit breaker off.b. Test the circuit for voltage.c. Post notice at the breaker box … DO NOT TURN ON.d. all of the above

POSTTEST



1. Answer: d. 5 to 1

2. Answer: e. Any of the above could be the cause.

3. Answer: d. add fluid to the reservoir

4. Answer: b. the lever

5. Answer: d. the screwThe screw is considered by some as a variation ofthe inclined plane.

6. Answer: a. fluid pressure

7. Answer: d. the fuse for the stereo system audio-outputblew.The volume caused too much current draw at thespeakers, so the stereo fuse blew.

8. Answer: d.Answer d is the only diagram with a closed switchto make a complete circuit.

POSTTEST


29. Answer: a. an ohmmeter

An ohmmeter measures ohms. An ammetermeasures amps and a voltmeter measures volts.

10. Answer: c. Check to see if the batteries are insertedcorrectly.

11. Answer: c. Check to see if there is water pressure at thebathtub faucet.

12. Answer: b. add resistors to the circuit.

13. Answer: a. 3 amps6 volts ÷ 2 ohms = 3 ampscurrent flow = 3 amps

14. Answer: c. 1 ohm12 volts ÷ 12 amps = 1 ohmresistance = 1 ohm

15. Answer: a. 24 volts6 amps × 4 ohms = 24 voltsvoltage = 24 volts

POSTTEST


216. Answer: d. Make sure both the microwave and stove are

properly grounded.Answers a, b, and c may prevent electrical currentfrom flowing, but they are not reasonable solutionsto the problem.

17. Answer: b. The light sockets are on a series circuit.

18. Answer: b. The power usage exceeds the circuit-breakercapacity.

19. Answer: d. Have an electrician add a 240-volt circuit.

20. Answer: d. all of the above

POSTTEST


2The following chart will provide you with scoring information. Count thenumber of correct answers on your Posttest. Find that number in the leftcolumn. The number in the right column is your score. Repeat the exercisesthat you missed and, if needed, go back to the lesson that talks about thosetopics.

NUMBER OFNUMBER OFNUMBER OFNUMBER OFNUMBER OFCORRECT ANSWERSCORRECT ANSWERSCORRECT ANSWERSCORRECT ANSWERSCORRECT ANSWERS SCORESCORESCORESCORESCORE

20 100%

19 95%

18 90%

17 85%

16 80%

15 75%

14 70%

13 65%

below 12 review entirelevel

YOUR SCORE


2Well, how did you do on the Posttest? If you

scored 90% or higher, you are ready for Level 3.Don’t be discouraged if you scored below 90%.There are a lot of skills to learn. You can do it!

Remember, learning basic skills in AppliedTechnology will help you in the workplace andthroughout your life.

GoodJob!

SUMMARY


2GLOSSARY

absorption - the process of heat (or other matter) being taken into asubstance

adaptation - the process of adjusting or changing forms

alloy - different types of metals that have been melted and blendedtogether

alternating - current electricity (AC) - a type of electricity thatpulsates

ammeter - instrument to measure electric current

ampere (amp) - a unit measure of current flow

attract - draw to

battery - a combination of materials for producing a direct voltage

bearing - a machine part to reduce friction on which parts turn or slide

circuit - complete path of an electric current

circuit breaker - a switch that interrupts an electric current whenconditions are not normal

circumference - the perimeter or outside distance around a circle

compound - made up of two or more parts

compression - a process of pressing or squeezing together

condensation - the process of a gas changing into a liquid

conduction - the transfer of heat through matter or the passage ofelectricity

conductor - matter with a large number of free electrons

conduit - a path or channel

REFERENCE


2current - the flow of electrons

cycle - one complete performance of an electronic ocillation, or a seriesof changes that moves something away from and then back to itsoriginal state

cylinder - long, round body or figure

density - a measure of the closeness of molecules in matter

diameter - thickness; length of a straight line through the center of anobject

direct-current electricity (DC) - a type of electricity with a constantlevel of output

electricity - a form of energy comprising elementary particles that exertenergy that exert force on one another

electrode - a conductor used to establish contact with a nonmetallicpart of a circuit

electrons - electrically charged particles of matter

energy - the capacity for doing work

evaporation - the process of changing a liquid into a gas

excessive - beyond the normal amount

fluid dynamics - the use of liquids and pressure

foot-pound - the measure of work or energy required to move an objectone foot against one pound of resistance

force - a push or pull

friction - creation of resistance and heat when matter rubs against matter

gas - matter that can move from place to place and be easily compressed

gauge - measure

gravity - attraction of matter toward the center of the earth

REFERENCE


2grounding - an electrical connection with the earth

heat - form of energy transferred between two bodies as a result of theirdifferences in temperature

hertz - a measure of cycles per second (cps)

hydraulics - the use of pressure transmitted through liquids to exertforce

hydroelectric - related to producing electricity by waterpower

inertia - tendency of matter to remain at rest or in motion

insulation - the effect of limiting the amount of transfer of heat,electricity, sound, or other forms of energy

inversely - opposite

insulator - matter with few free electrons

leg - a section or branch of an electrical circuit

load - a device to which power is delivered; power output or consumption

lubricant - substance that reduces friction

mass - a measure of the amount of material in an object

matter - material substance of which any physical object is made

maximum - greatest amount

mechanical advantage - a gain from the use of a machine to transmitforce

mechanics - a science that deals with energy and forces and their effectson bodies

meter - a measuring device

minimum - lowest amount

molecule - small particles that make up matter

REFERENCE


2molten - melted or made into liquid by heat

ohm - a unit measure of resistance

ohmmeter - instrument to measure ohms

outlet - a receptacle for the plug of an electrical device

parallel circuit - a circuit that provides more than one path for currentflow

particles - any of the basic units of matter

polarity - state of having opposite qualities or powers, such as positiveand negative

pressure - the application of force

principle - a law or fact of nature

reflection - the act of bending or throwing back energy, such as light,heat, or sound

repel - drive or push away

resistance - an opposing force

resistor - electric circuit device used to control current (creates resistance)

series circuit - a circuit that has one or more loads in a single-circuitloop from a power source

short (short circuit) - a condition of low resistance between two pointsof different potential in a circuit, usually resulting in a flow ofexcess current and an inoperable circuit

sphere - round body; a globe

static electricity - a type of electricity created when certain matter isrubbed together

substation - a place where electric voltage is controlled for local

REFERENCE


2distribution

switch - simple device to turn a device on or off

technology - the use of tools or methods to do work more easily

terminal - device for making an electrical connection

thermodynamics - the influence and use of heat

transformer - a device to change electric voltage in potential or form

voltage - a unit used to measure pressure or the push of electrons througha circuit

volume - a measurement of space occupied, expressed in cubic units

wave - a fluctuation that transfers energy from point to point

weight - a measurement of gravity’s pull on forms of matter; a measureof heaviness

REFERENCE

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Toll-free 888.717.9461Fax 865.717.9461 www.w-win.com

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