electric principles and technology - holy cross collegiate student... · web viewvolt (v), named...

Mrs. Sample

Christ the Redeemer Catholic Schools

Science 9

Science 9Electric Principles and Technology

Topic 1: Electrical Charges

Materials that attract and repel other materials are said to be charged, or carry an electrical charge.

Electric charge can be detected by an instrument called an __________________________. Pocket-sized electroscopes called _______________________ are used to measure exposure

to atomic radiation. In many cases, charges produced by rubbing or touching materials remain stationary, so they

are sometimes called static electricity. There are many instances when these charges move, so unbalanced charges is a more accurate way of describing the phenomenon.

The quantity of electric charge is expressed in coulombs (C). A bright light bulb allows about 1 coulomb of electric charge to pass through it every second.

Making Sense of Electric Charges The charge on an object depends on the balance between positive and negative charges in the

object.a) neutral (“ uncharged”) have _________________________________________________b) positive charge has ________________________________________________________c) negative charge has _______________________________________________________

Benjamin Franklin was the first to use the terms “positive” and “negative” to describe charges.

The charge on amber that had been rubbed with fur was called ________________________. The charge left on the fur was called _________________________. Unbalanced charges on solid materials are due to

___________________________________ from one object to another.

The Laws of Charge:1. Unlike charges attract.2. Like charges repel. 3. Charged objects attract uncharged (neutral) objects.

Conductors, Insulators, and In-between _________________________ are materials that do not allow

charges to move freely on or through them. Materials that allow charges to move freely are classified as _______________________. Most metals are conductors and most non-metals are insulators A conductor holds its electrons ___________________. Insulators hold their electrons ____________________________.

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Figure 1: The Laws of Charges

Semiconductors are materials with ______________________________________________ __________________________________________________________________________.

The conductivity of semi-conductors is often increased by implanting foreign atoms into the otherwise pure material.

Two commonly used semiconductors are _____________ with ______________ added, and ______________________ with _____________________ added.

Superconductors are materials that offer little, if any, resistance to the flow of charges. Certain materials become superconductors when they are subjected to extremely low temperatures. Superconductors _________________________________________________ _________________________________ than ordinary conductors.

Neutralizing Unbalanced Charges An electric discharge occurs when accumulated charge is neutralized (becomes balanced) In a discharge, electrons either _________________________________________________,

or ________________________________________________________________________. Connecting an object to Earth with a conducting wire –____________________________- is

an easy way to neutralize conducting materials Non-conductors, or insulators, usually must be neutralized with ionization. Ionization

devices produce both positive and negative ions. These ions are attracted to materials with an opposite charge, transferring charges until the material is neutralized.

Preventing Electrostatic Buildup To decrease static buildup, antistatic sprays and coatings can be applied to carpets and other

surfaces on which charge accumulates. After materials have become charged, sprays can also be used to dissipate (scatter) the

charge. Materials that are especially sensitive to electrostatic discharge may be enclosed in special

antistatic packaging. Grounding straps containing conductive materials may neutralize without harmful electric

discharge.

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Topic 2: Electricity Within a Circuit Electric circuits provide a continuous pathway.

Circuit Elements and Diagrams Most complex circuits are made up of only four basic

elements. ________________: The source of electric energy. ____________________: The wire through which

current flows. ____________: Items along the circuit that convert

electricity into other forms of energy. _____________: A switch or device that can turn

the circuit or devices along it on or off. A battery is a combination of cells. You can use a switch to “open” or “close” a circuit to

control the flow of current through it. A resistor is used to represent one of many different

loads.

Measuring Current Electric current is ___________________________________________________________

___________________________________________________________________________ The symbol for the current is I. Electric current is measured in amperes (A) or milliamperes (mA). An instrument used to measure very weak electric current is called a galvanometer. Larger

currents are measured with an ammeter of milliammeter. The symbols for these instruments are a circle with “G,” “A,” or “mA” in the center, respectively.

Measuring Voltage The energy for pushing electrons through comes from separated positive and negative

charges. In a battery, _____________________________________________________ does the work

of separating the charges. All forms of energy are measured in joules (J). The energy of electrons in an electric circuit is described by a standard unit of charge instead

of the total energy of all of the changes. Potential difference means the difference in energy per unit of charge between one point in

the circuit and another point in the circuit. Potential difference is commonly referred to as voltage. The standard unit for potential difference is the volt (V), named after Alessandro Volta (1745-1827), who built the first battery. Voltage is measured with a voltmeter; the symbol for a voltmeter is a circle with “V” at the centre.

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Figure 2: Basic Circuit Symbols

Current and Voltage Electric current is equal throughout a circuit. For the electric current to flow in a circuit, the battery must be supplying energy & there

must be a continuous pathway for the electric current to travel. Factors that affect the strength of an electric current in a circuit include

_____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________

Batteries provide electrical energy. Loads use electrical energy. The energy provided to a circuit is very close to the energy used. The voltage across individual loads adds up to a voltage very similar to the voltage across the

entire load. Voltage is higher when loads are removed because there is less resistance within the circuit.

Rivers of Electricity The load of an electrical circuit is comparable to a water wheel in a water system:

A switch is comparable to a valve An electrical current is comparable to a flow rate Voltage is comparable to pressure A battery is comparable to a pump A conductor (wire) is comparable to a pipe

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Topic 3: Resisting Movement of Charge Resistance is a property of a substance that _______________________________________

____________________________ and converts electric energy into other forms of energy. If current is described as the movement of electrons through conductors, and voltage is what

makes the electrons move, then resistance is what opposes the motion of the electrons. A good conductor has low resistance. Poor conductors have high resistance.

Resistance Roadblock Nichrome wire is a resistor. The standard unit for resistance is the ohm( ) Resistance can be measured with an ohmmeter Technicians are more likely to use a multi-purpose electronic

measuring instrument (a “multimeter”) set to measure resistance Ohm’s law: R=V/I

ie. Resistance = Voltage (potential difference)/ Current Other forms of the equation are: V = IR and I = V/R

Example: What is the resistance of an electric heater, if a current of 12.5 A runs through it when it is connected to a 120 V wall outlet? (9.60 Ω)

Example: What is the resistance of a light bulb if a 12 V battery sends a current of 2.4 A through it? (5.0 Ω)

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Example: A toaster with a resistance of 145 Ω is connected to a 120 V source. What current will flow through the toaster? (0.828 A)

Example: What is the potential difference across a 1500 Ω resistor carrying a current of 0.075 A (75 mA)? (112.5 V)

Example: An extension cord rated at 15 A is connected to a 120 V supply. What is the smallest resistance with which the cord can safely be used? (8 Ω)

Resistors In electronic circuits, resistance is useful for:

1) Changing the energy of moving charges into heat.2) To control current or voltage to suit the specific needs of other electric devices in the

circuit. Circuit resistors are usually made of a heat-conducting ceramic core coated with materials such as carbon, metal oxides, meal film, or resistance wire

Variable Resistors Variable resistors change in response to __________________________________________

__________________________________________________________________________. Varying the length of a Nichrome wire can act as a variable resistor. The longer the length,

the more resistance there is. Variable resistors are used in light dimmers, motor speed controls, surge protectors, and

refrigerator and stove temperature controls. Variable resistors are also called rheostats.

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Types of Circuits1) _________________________ have only one current path.2) _________________________ have several current paths.

Series and Parallel Circuits

Series Circuits As more bulbs are added in a series circuit,

______________________________________ because there are more resistors for the current to travel through-more bulbs mean less current.

In a series circuit all loads must be functional & all switches closed for any of the loads to work

Advantages of series circuits:1)______________________________________________________2) Less wire3) ______________________________________________________

Disadvantages of series circuits:1) Additional bulbs mean dimmer lights2) ____________________________________________________________________

Parallel Circuits Adding more bulbs to a parallel circuit does

not decrease the brightness of the bulbs. More bulbs increases the current.

In a parallel circuit not all loads need to be functional for the circuit to work because there are a number of paths the current can travel

Advantages of a parallel circuit1)_____________________________________________________________________2) Other loads continue to work even though one may not be working.

Disadvantages of a parallel circuit1) _____________________________________________________________________2) Wires heat up with increased current flow3) ____________________________________________________________________

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House Wiring Practical electric circuits for the home are _____________________________. The voltage

across each load in a parallel circuit is the same. Turning on one appliance will not reduce the energy available to other loads.

One potential problem does exist with parallel circuits. Current through wires connected to the source increases whenever another branch in the circuit is closed. When you turn on any appliance in your home, the current in the wires closest to the source increases. More current means the temperature of the conducting wire rises.

The wires _______________________________________________________________. To guard against an electrical fire, household circuits always include ______________________ __________________________________.

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Topic 4 - The Energy Connection

The scientific definition of energy is ____________________________________________. The four most common forms of energy are:

o _________________________: potential or stored energy stored in chemicals, released when the chemicals react

o _________________________:energy of charged particles, transferred when they travel from place to place

o _________________________: energy possessed by an object because of its motion or its potential to move

o _________________________: kinetic energy of a substance

Electricity and Heat Thermal energy can be converted directly to electric energy using a

thermocouple. A thermocouple is a loop of two wires made of different types of metals. The wires are wrapped together at both ends, or “junctions.” When one junction is heated, ______________ ______________________________________________________

Copper and constantan (a copper nickel alloy), or iron and constantan, are the most common metals used in modern industrial thermocouples.

A thermo-electric generator is a device based on a thermocouple that converts heat directly into electricity without moving parts. Heat from a gas burner or another heat source moves though several thermocouples connected in series – a thermopile – creating a potential difference. Thermopiles are extremely reliable, low-maintenance devices. They are used in remote locations to generate limited quantities of electrical energy that are sufficient to power, for example, emergency communications equipment.

Electricity to Motion Sound can be produced when __________________________________________________

_____________________________________________________ – the piezoelectric effect. Piezo in Greek means pressure or push. When a piezoelectric crystal such as quartz or

Rochelle salt is connected to a potential difference, the crystal expands or contracts slightly. Material touching the crystal experiences pressure, creating sound waves or vibrations.

Motion to Electricity A barbecue “spark” lighter uses the piezoelectric effect in reverse. While a piezoelectric

crystal is being compressed or pulled, a potential difference is built up on the opposite sides of the crystal. _______________________________________________________________ __________________________________________________________________________.

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Electricity to Light Piezoelectric crystals can produce light ___________________________________________ Some recent types of flashlights do not have a light bulb. Instead they have ______________

_________________________________________________________________ LEDs use only a fraction of the power of a traditional bulb and last for years as opposed to

months

Light to Electricity The device that is most commonly used to produce electricity from light is called a

photovoltaic (PV) cell, or solar cell. PV cells are made of _________________________________________________________.

When light strikes the cell, light is absorbed by the semiconductor material, breaking electrons loose and allowing them to flow freely

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Topic 5: Portable Power An electrochemical cell is an electrical cell consisting of different metal electrodes in a

solution containing an acid or salt.

Electrochemical Cells In any electrochemical cell, two metal electrodes are surrounded by an electrolyte, ________

__________________________________________________________________________. “Wet cells” use _____________________________________________________________. “Dry cells” have ____________________________________________________________.

Figure 3: A Typical Wet Cell Battery Figure 4: A Typical Dry Cell Battery

In a typical aluminum-copper wet cell, when the cell supplies current to a circuit, atoms of

aluminum become ions and go into the electrolyte solution. This electrode (the negative anode) is consumed as the cell operates. The other electrode, the positive cathode, release electrons which are taken up by the

anode. Very few single cells can produce more than 2 V. To obtain higher voltages, _____________

___________________________________________________________________________ A primary cell is one that __________________________________________. Rechargeable secondary cells use chemical reactions, which can be reversed. Fuel cells combine hydrogen and oxygen without combustion. ________________________

__________________________________ are the only by-products of the fuel cell’s reaction.

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Topic 6: Generators and Motors

Electromagnets When a soft iron core is inserted into a coil of wire and a current is passed through the wire,

an even stronger temporary magnet called an electromagnet is created.

Factors that Affect the Strength of Electromagnets: _________________________________________________________ increase the strength. Increasing the current also results in a stronger magnet.

Magnetism to Electricity A potential difference (voltage) is “induced” in a wire when __________________________

__________________________________________________________________________. When the wire is connected to a circuit, an “induced current” flows.

What’s in a Generator? A generator produces electric current by __________________________________________

_______________________________ or by ______________________________________ ___________________________. As wires in the coil rotate, electrons begin to move along the wire in one direction.

After one-half revolution of the wire loop, each side of the coil passes near the opposite pole of the magnet. This causes the electrons in the coil to start moving in the other direction.

Electricity produced by this type of generator is called alternating current (AC) because it changes direction, or “alternates”. Power plants produce alternating current because _______ __________________________________________________________________________.

DC Generators A generator that produces direct current is often called a dynamo. In a dynamo, the armature (rotating loop of wire) is connected to the outside circuit by a

______________________________________________ As the armature and commutator rotate, insulating gaps in the commutator momentarily stop

the flow of electric current. As the gaps move past the brushes, current resumes but in the opposite direction. At this point the direction of charge flow from the armature has reversed but so has the

connection through the commutator. As a result, current continues to flow through the load in the same direction.

Electric Motors: Electric to Mechanical Energy A motor uses electric energy to make a coil of wire spin between the poles of a magnet (the

“field magnet”).

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Current flowing through the coil turns it into an electromagnet, which is rotated by magnetic forces from the field magnet.

DC Motors In one common design for DC motors, a rotating wire coil (an armature) becomes an

electromagnet as current flows into it through a split-ring commutator. The armature is _________________________________ by stationary field magnets near it,

so it begins to rotate. The commutator acts as a _______________, cutting off and then reversing the direction of electron flow to keep the armature turning.

AC Motors AC motors have a rotation core, rotor, made up of a ring of non-magnetic conducting wires

connected at the ends and held in a laminated steel cylinder. Surrounding the rotor is a stationary component called a stator. The stator is a two-pole (north and south) electromagnet. When an AC motor is turned on, the attraction and repulsion between the magnetic poles of

the stator and the rotor causes the rotor to spin.

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Topic 7: Electricity in the Home

Transformers are used to “step up” the voltage for efficient transmission over long distances.

Other transformers “step down” the voltage to the 240/120 V used in homes and factories.

A fuse contains a metallic conductor that melts when excessive current heats it up. This opens the circuit until the fuse is replaced.

A main circuit breaker acts as a switch and safety device that can cut all power coming into the home.

If current exceeds a safe level, a bimetallic strip in the breaker heats up, bends, and opens the circuit.

The individual circuit breakers in the service panel controls branch circuits located throughout the entire house.

A branch circuit supplies power to one or more wall plugs or lights connected in parallel by cables in the house walls. As additional loads are plugged into a branch circuit, the current

flowing through the connecting cables increases. The small resistance of the cable wires causes them to heat up when enough current flows

The breakers, plugs, lights, and switches in each branch circuit are connected by two “live” wires – a white insulated wire (usually called the neutral wire) and a black insulated wire (usually called the hot wire). The third wire is the ground wire. It reduces hazards by safely channeling back into the ground any current that has “leaked” onto metal components in the electric circuit.

Digital Devices Digital electronic technology – machines that process numerically coded information. A Binary code is two states (on or off) that represent numbers and letter. Logic circuits containing many switches can process binary information. The electronic switches in modern digital devices are transistors, that can be turned on and

off by electric signals. Every digital device you use is designed around components that contain enormous numbers

of transistors.

Measuring Electric Power Power is energy per unit of time.

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Electric power describes ______________________________________________________ ___________________________________________________________________________

Electric power can also describe the amount of electric energy that is transferred from one place to another in a certain amount of time.

power (¿watts )= energy(¿ joules)time(¿ seconds)

– or –

P= Et

One joule per second is also called a _______________ Electric power is not usually calculated directly by measuring energy and time. It is much

more common to measure the voltage and current in a circuit and use these quantities to calculate power

power (¿watts )=current (¿ amps )× voltage (¿volts)

– or –

P=I ×V

Example: A current of 13.6 A passes through an electric baseboard heater when it is connected to a 110 V wall outlet. What is the power of the heater? (1.50 ×103 W)

Example: What is the power (in watts and kilowatts) of a hair dryer that requires 10 A of current to operate on a 120 V circuit? (1200 W)

Example: The maximum current that a 68.5 cm television can withstand is 2 A. if the television is connected to a 120 V circuit, how much power is the television using? (240 W)

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Example: A 900 W microwave oven requires 7.5 A of current to run. What is the voltage of the circuit to which the microwave is connected? (120 V)

Example: A flashlight using two 1.5 V D-cells contains a bulb that can withstand up to 0.5 A of current. What would be the maximum power of the bulb? (1.5 W)

Paying for Electric Energy Most power companies measure electric energy in a customary unit – the kilowatt hour

(kWh). One kilowatt hour is the total energy supplied to a 1000 W load during 1 h of operation.

Solving Cost of Power Problems1. Determine the # of kW of power used.

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2. Multiply the # of kW by the # of hours to get kwh.3. Multiply the # of kWh by the cost/kWh

Example: A family uses 3000 kWh of electric energy in a two-month period. If the energy costs 11.0 cents per kilowatt hour, what is the electric bill for the period? ($330)

Example: If a refrigerator requires 700 W of power to function, how many kilowatt hours of power will it require in a 30-day period? (504 kWh)

If electricity costs 11 cents per kilowatt hour, how much would the refrigerator cost to operate in that period? ($55.44)

Example: A home-owner finds that she has a total of 42 light bulbs (100 W) in use in her home.(a) If all of the bulbs are on for an average of 5 h per day, how many kilowatt hours of

electricity will be consumed in a 30-day period? (630 kWh)

(b) At 11 cents per kilowatt hour, how much will operating these lights cost the home-owner during that period? ($69.30)

(c) How much money would the home-owner save if she switched all of the bulbs to energy-saving 52 W light bulbs? ($33.26)

Example: Bob has a stereo that operates at 120 V, using 2.5 A of current.(a) How much power does Bob’s stereo need to operate? (300 W)

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(b) If Bob plays his stereo for an average of 5 h each day, how much electricity will he use in a 30-day period? (45 kWh)

Electric Devices and Efficiency If an electric light bulb were perfect, all of the electric energy it took in

(_____________________) would be converted into light (__________________________). No real device, however, is a perfectly efficient energy converter. Some input energy is always converted into waste heat.

You can express efficiency as a percentage using the following mathematical relationship.

efficiency=useful energy outputtotalenergy input

× 100

To find the efficiency of electric devices, it is often necessary to calculate energy inputs or

outputs. To determine the electric energy input of a device, the formula for power (P=Et )

can be manipulated to solve for energy.

Efficiency of Common Light Bulbs Incandescent bulbs are about ______ efficient, which means about _______ of the input

electrical energy is converted to waste heat. Halogen bulbs are filled with high-pressure gas containing traces of iodine

Halogen bulbs are about _________ efficient, Last two to six times longer than incandescent bulbs

Fluorescent tubes convert about ________ of the total input energy into useful light energy Last 10 to 13 times longer than incandescent bulbs, and are much more expensive

Example: A 1000 W electric kettle takes 4.00 min to boil some water. If it takes 1.96 ×105J (196 000 J) of energy to heat the water, what is the efficiency of the kettle? (81.7%)

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Example: Find the efficiency of a 23 W fluorescent tube that is used 4.0 h per day and in that time produces 6.624 × 104J of useful light energy. (20%)

Example: A 100 W incandescent bulb also produces about 6.624 × 104J over a 4.0 h period. What is the efficiency of this bulb? (4.6%)

Example: Based on your answers to the previous two questions, how much money would you save in a 30-day month if you replaced 25 of the 100 W incandescent bulbs with 23 W fluorescent bulbs? Assume the bulbs operate 4 h daily, and that electricity costs 10¢ per kWh. ($23.10/month)

Home Electric Safety Do not overload an outlet or a circuit. Never work on or clean appliances that are still plugged in.

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Replace frayed or worn out electric cords. If the bare wires touch directly (a short circuit), a high current flows between them, causing

sparks and often starting a fire. Use receptacle cover on easily accessible outlet. Never use appliances close to a sink of bathtub with water in it or when your hands are wet. Ground fault circuit interrupter, a GFCI monitors current flowing into and out of a load. If

any electricity is diverted out of the circuit wires, the GFIC immediately cuts off the current.

Electric Safety Outdoors Never allow your body or something you are holding to come into contact with live electric

wires. Never use ungrounded or frayed two-prong electric cords outdoors. Do not operate electric equipment outdoors when it is raining. Before digging deeply in your yard, make sure that there are no underground utility cables.

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Topic 8: Electricity Production and the Environment

Electric Energy from Burning Fuels Fuel oil, natural gas, and coal, are burned in large __________________________________

___________________________ to produce about one quarter of our country’s electricity.

Fossil Fuels Affect Land and Air Open pit mining of surface deposits disturbs soil and vegetation. Underground mines produce waste materials called “tailings,” which accumulate near the

mine. Water seeping through the tailings becomes ______________________________________. When fossil fuels are burned, contaminants such as visible particles and invisible gases

escape form smokestacks. ___________________________________________ can remove most of the solid particles. Scrubbers can remove sulfur dioxide. Scrubbers spray a water solution through the waste

gases. SO2 and other pollutants react with chemicals in the water and are removed. Complete burning of pure coal or natural gas would produce _________________________. Carbon dioxide is a greenhouse gas, which means that it helps delay the escape of heat from

Earth’s atmosphere. This could lead to a rise in the average temperatures on Earth- global warming.

Natural gas _________________________________________________________________ __________________________________________________________________________.

Electric Energy from Flowing Rivers Hydro-electric plants use water pressure to generate electric energy. Hydro-electric power

plants appear to be a very clean form of electric energy generation. However, reservoirs, which store behind the dams, __________________________________________________. Homes, small villages, and even entire towns may need to be moved, displacing people and industries.

When submerged vegetation decays, micro-organisms responsible for this process use up the oxygen supplies in the water.

Sometimes decaying matter produces methane gas Other forms of life, such as algae, take over and change the ecosystem.

Energy From Atomic Reactions Bombarding uranium atoms with tiny particles called neutrons causes the uranium to split

into two smaller atoms. In the process called _____________________________, a tremendous amount of energy is

released. This is referred to as __________________________________________________.

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Fission reactors do not release soot or gases that cause acid rain, nor do they release greenhouse gases. However, used (spent) reactor fuel is _____________________________ ________________________________________________________

The reactors themselves also become slightly radioactive so they are difficult and expensive to decommission.

In the Sun and other stars, nuclear fusion joins very small atoms to form a larger atom. Huge amounts of energy are released in this process

Developing technology to create and use continuous controlled fusion as a power source is an extremely difficult and expensive project.

Heating the Environment All thermonuclear and thermo-electric-generating plants release thermal energy into the

environment. Thermal pollution occurs when this warm water is returned directly to the lake or river from

which it is taken, increasing the water temperature. Even a change of a few degrees can affect the plant and animal life in the water.

To reduce thermal pollution, large generating plants have cooling ponds or towers where waste water can return to the temperature of the surroundings before it is released.

Cogeneration It makes environmental sense to design electricity-generating stations as cogeneration

systems that produce electricity and also supply thermal energy, such as hot water or steam, for industrial or commercial heating.

Alternative Energy Sources Energy from the Sun, wind, and tides, which until now has been too expensive or too

difficult to harness, is rapidly becoming competitive with conventional energy sources. Wind-driven electricity generation must be used together with other electric energy sources

or storage devices. Solar-powered-generating systems often include storage batteries to supply electricity at

night or in cloudy conditions. Ocean tides are another source of energy that can be used to generate electricity. The hot inner parts of the Earth contain a great deal of thermal energy, called geo-thermal

energy. Ground water flows down from the surface, absorbs thermal energy, and rises again as hot spring and geysers. Steam produced by geothermal activity can be used to rotate turbines and turn electric generators.

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Sample PAT Questions (from 2008 and 2010)

1. When clothes are removed from a clothes dryer, sparks can be seen as the clothes are separated. These sparks are a result of

A. current electricityB. an electrical dischargeC. a buildup of neutral atomsD. anti-static sheets absorbing neutral charges

Use the following information to answer the next question.

Facts About Electricity

I Electrons can be discharged when clothes are removed from a clothes dryer.II Electrons flow continuously through a conductor.

III Electricity can be used to operate a motor.IV Electricity can build up and produce lightning.

2. Which facts describe properties of static electricity? A. I and IIIB. I and IVC. II and IIID. II and IV


3. The total electrical energy consumed by Joe’s television isA. 33.3 JB. 108 JC. 1.20 kJD. 4.32 MJ


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4. Which change could Roger make to the wet cell to produce electricity? A. Replace one of the zinc electrodes with copper. B. Increase the sulfuric acid concentration to 7.5%.C. Replace both of the zinc electrodes with copper. D. Decrease the sulfuric acid concentration to 2.5%.


5. The total electrical energy consumed by Joe’s television isA. 33.3 JB. 108 JC. 1.20 kJD. 4.32 MJ

6. Which of the following sequences shows the transfer of energy initiated by the flow of water in a hydroelectric power plant?

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A. Mechanical-gravitational-electricalB. Electrical-gravitational-mechanicalC. Gravitational-electrical-mechanicalD. Gravitational-mechanical-electrical

7. Which of the following modifications to an electromagnet will increase its strength? A. Using a larger iron coreB. Using fewer coils of copper wireC. Increasing the resistance of the iron coreD. Decreasing the current passing through the coils of copper wire

8. Which of the following sets of components in a series circuit would cause the light bulbs to shine the brightest?

Row Resistance LoadA. Resistor present 2 bulbsB. Resistor present 3 bulbsC. No resistor present 2 bulbsD. No resistor present 3 bulbs


A student explains how electric circuits function by comparing them to a traffic model. Some of the components of traffic are listed below.

Traffic ComponentsI

IIIIIIV

Road construction sitesStop signsVehiclesRoads

9. Which component of the traffic model is most closely related to switches found in circuits? A. IB. IIC. IIID. IV


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10. Which of the following diagrams represents the circuit described above?

11. Which of the following sources of energy is classified as renewable ?A. Natural gasB. BiomassC. CoalD. Oil

12. Which of the following wet cells would produce the highest voltage?

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13. To the nearest tenth of a watt, how much power does the bulb consume (P = IV)?A. 0.5 WB. 2.0 WC. 13.4 WD. 39.6 W


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14. The resistance in the circuit shown above isA. 2 ΩB. 3 ΩC. 4 ΩD. 6 Ω

15. Tungsten is used as a filament in some light bulbs because itA. allows electrons to flow easilyB. allows protons to flow easilyC. resists the flow of electronsD. resists the flow of protons

16. A disadvantage of hydroelectric power generation is that itA. emits pollutants into the atmosphereB. disrupts the natural flow of waterwaysC. provides an unreliable method for producing energyD. produces hazardous waste that requires long-term storage


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17. Which of the following statements predicts the relative brightness of each of the three light bulbs in the circuit shown above?

A. Light bulb 1 is dimmer than light bulb 2, which is dimmer than light bulb 3. B. Light bulb 1 is brighter than light bulb 2, which is brighter than light bulb 3. C. Light bulb 1 is dimmer than light bulbs 2 and 3, which both have the same brightness. D. Light bulb 1 is brighter than light bulbs 2 and 3, which both have the same brightness.


18. Which motor component functions as an electromagnet? A. Permanent magnetB. Power sourceC. CommutatorD. Armature


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19. Which component in the circuit shown above is protected by the circuit breaker when both switches are closed?

A. Furnace motorB. Exhaust fanC. HeaterD. Light

20. An electrical device with low efficiency is most likely to produce excessA. heat energyB. light energyC. sound energyD. mechanical energy

Use the following information to answer numerical response question 1.

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Kelly recorded the input energy and output energy of four electric devices.

Device Input Energy (J) Output Energy (J)1 10 32 71 163 100 274 950 510

Numerical Response

1. When listed in order from the most efficient device to the least efficient device, the order is

_____________, _____________, _____________, and _____________Most efficient Least efficient

Use the following information to answer numerical response question 2.

In order to produce 100 000 J of heat energy, a hot plate consumes 800 000 J of electrical energy.

Numerical Response

2. To the nearest tenth of a percentage, the efficiency of the hot plate is _____________%.

Answers: 1. B2. B3. D4. A5. D6. A

7. A8. B9. C10. B11. D12. A

13. C14. D15. C16. B17. B18. D

19. A20. ANR1. 4132NR 2. 12.5

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