ENERGY AND THE ENVIRONMENT
ENERGY AND THE ENVIRONMENT PHSC 1014
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This 21 page Class Notes was uploaded by Louisa Volkman DDS on Friday October 2, 2015. The Class Notes belongs to PHSC 1014 at Arkansas State University taught by John Pratte in Fall. Since its upload, it has received 42 views. For similar materials see /class/217717/phsc-1014-arkansas-state-university in Physical Science at Arkansas State University.
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Groundlevel Ozone Your Vehicle Introduction This exercise examines groundlevel ozone the air pollution commonly referred to as quotsmogquot quotsmokequot quotfog quotsmogquot Smog is formed by a combination of air pollutants and sunlight and ca have adverse effects on humans and other organisms You have likely heard of ozone in a different capacity Ozone also occurs high above Earth39s surface in the stratosphere where it serves a protective function by blocking harmful ultraviolet radiation from the Sun The ozone in each case is the same molecule but in one location high in the atmosphere it is bene cial to living things while at another location groundlevel it is harmful The major differences between stratospheric and groundlevel ozone is reviewed in the brochure below from the US Environmental Protection Agency Ozone Good Up High Bad Nearby Online database of vehicle fuel ef ciencies U Department of Ener httpesa21kennesaweduactivitiessmogcar epagooduphighpdf Groundlevel Ozone Vehicles The goal of this exercise is to quantify and analyze your personal contributions of smogforming compounds due to driving As detailed in the brochure vehicles can be a significant contributor of the compounds that cause groundlevel ozone In this exercise you will estimate the amount of smogforming compounds from driving an investigate how you might reduce this To begin your analysis let39s review information on vehicles and ozone with an online brochure from the Federal Highway Administration of the US Department of Transportation on Transportation Air Quality l ll NW Fig 1 Los Angeles smog EPA Vehicle Emissions PDF 448 KB United States Federal Highway Administration Department of Transportation pwwwfhwadotgovenvironment To estimate the amount of ozoneforming compounds generated by your car we will use data from the Department of Energy s FueIEconomy web site This site allows you to see how your car rates on air pollution emitted as well as estimating the tonnage of greenhouse gases emitted driving an average number of miles As you learned in the Transportation Air Quality brochure a number of factors in uence NOX and VOC emissions from vehicles While this data does not take all of these factors into account it does provide a good estimation of your emissions Groundlevel Ozone YourVehicle 1 Air Emission Data FuelEconomygove httDWWWquot 39 vnv quot 39 39 39 39 39 39 39NFshtm1 Tailpipe Data 1 Seect your vehicle s make and model engine from the website From the list of Idifferent engineiproifiles choose the appropriate one Write down your data 2 Go backto the initial page Choose a 2009 Toyota Prius which is a hybrid Vehicle Write down the data on the activity sheet Go back to the initial page This time choose a 2009 Ford Escape Hybrid FWD Record the data on the activity sheet Lastly go backto the initial page This time select a 2009 Toyota Yaris automatic Record the data on the activity sheet 9 5 To find the price for these cars go to Kelly Blue Book httng Wwwkbbcomi7ind1 ithie makes and models and enter the information on the activity sheet Air Pollution and Asthma DO NOT COMPLETE THIS SECTION UNTIL YOU39VE COMPLETED THE ACTIVITY ABOVE You are undoubtedly aware that many parts of the US have annually reoccurring smog problems Metropolitan areas like Los Angeles Houston Atlanta and others have often exceed federal air quality standards posing a health risk to individuals living in the area While everyone can experience health problems from smog it is particularly severe for individuals with respiratory ailments such as asthma as air pollution can act as a quottriggerquot for respiratory attacks The American Lung Association states that 247 million individuals have been diagnosed with asthma and about onethird ofthem are children Asthma is particularly troubling in children as it is the number one cause of hospitalization and school absenteeism Asthma and Children Fact Sheet American Lung Association While most people are generally familiar with asthma many do not understand the ailment and how it affects lung function Learn about this by viewing an animated Flash tutorial on asthma from Neomedicus and Merck If you have a fast Internet connection choose the version with sound Use the quotno soundquot version with slower connections What s Asthma All About Neomedicus and Merck Requires Macromedia Flash player httpwwwwhatsasthmaorg Once you39ve familiarized yourself with this material complete the Analysis section on quotAsthma and Air Pollutionquot on the Activity sheet Groundlevel Ozone Your Vehicle 2 PHSC 1 01 4 Activity Sheet Groundlevel Ozone Name Tailpipe Tally Enter your vehicle s year make model emissions certification and annual miles driven below I Year I Make I Model Iquot 39 39 CertI Annual Miles Enter your annual outputs of nitrogen oxides and hydrocarbons for your vehicle in the space below Enterthe information for the first hybrid comparison in Hybrid 1 and the second hybrid vehicle comparison in Hybrid 2 being sure each time to list the make and model of the hybrid vehicle Circle whether each vehicle s emissions are higher or lower than your vehicle and enter the difference in emissions next to Amount Your Vehicle 2009 Toyota Prius 2009 Ford Escape 2009 Toyota Yaris Analysis Vehicle Emissions Compare your vehicle to the selected vehicles How did your vehicle compare Did this surprise you Given the prices of the cars which one would be the best to buy Why Groundlevel Ozone Your Vehicle 1 Asthma and Air Pollution You ve seen that asthma affects large numbers of individuals attacks can be induced by air pollutants pollution may act to cause individuals to develop the disease and asthma attacks are an extremely unpleasant event to endure You ve also likely seen that your current vehicle emits more ozoneforming compounds than a gasolineelectric hybrid vehicle Toyota Prius andor a typical compact car Ford Focus So here s the problem you are by choice releasing more harmful pollutants into the atmosphere than if you were to drive these other vehicles for exactly the same distance These pollutants induce attacks in asthmatics and may cause children and adults to develop asthma as a result of exposure to your pollution Is it morally problematic for you to drive a vehicle that gets lower mileage and hence releases more pollutants than another vehicle when you are aware of the adverse impacts of your choice on others You should address the question from a variety of viewpoints ethical scientific philosophical economic etc Think about the question carefully before answering and be sure to explaIn yourself fully Groundlevel Ozone Your Vehicle 2 Solar Energy Introduction Renewable energy is the key to a sustainable future All other forms of energy will eventually run out whether it is oil within the next century or coal within the next several hundred At some point in the future we will need to be totally reliant on renewable forms or else we will have nothing left to burn Renewable energy is also a key to a sustainable future in that it has a much smaller environmenta impact The largest impact for many renewable forms is the damage done in getting the materials to make the machinery to harvest the energy For some the onl other impact is aesthetic ugl solar panels and noisy windmills for others the impact can be fairly large river ecosystem converted to lake by hydroelectric However the overall impact is much smaller than fossil fuels or nuclear energy which has large extraction and waste problems The drawbacks to using renewable energy are availability and economics Some forms of renewable energy are not readily available in certain locations such as solar panels in a cloud forest In othe locations they might be available but at a cost tha makes them very uneconomical Some forms of renewable energy are uneconomical no matter where they are placed Activity In this activity we are going to look at the availability and economics of solar power where you live To do this we are going to need maps of available sunshine provided by the US government We are also going to need to know the price of solar panels that are commercially available Foremost though we are going to need to know how much electrical energy you use before we proceed to estimate the cost of using renewable energy Finding out how much electrical energy we use is actually quite easy All that one needs to do is to either monitor their electric meter for some period of time or review their electrical bills Either of these two methods will give you an exact amount for how much electricity you use However this value will tell you nothing a out the sources of your usage It will also only tell you what your usage was forth past which depended greatly upon conditions in the past such as the indoor and outdoor temperatures What we really want is a way of estimating your usage in the future and nding ways of controlling it In order to do this we are going to estimate how much usa e you have by looking at the individual appliances in your home While you have done this somewhat during the Home Analysis activity we did not get to the level of detail about various appliances that we will be doing with this new activity To help us in the venture we are going to use the Home Energy Saver online calculator from the US Department of Energ This calculator allows one to make as detailed an estimate as one would like or as general as possible In order to have an estimate that is as accurate as possible you will need to kn w some information about the appliances in your home suc as eir wattage an the amount of time that they are turned on during an average week If you cannot nd that information the calculator will allow you to choose national average values for wattages and time usage Using the calculator is quite simple At the front page put in your zip code You will be sent to a page to enter some basic in ormation about your home such as he date that it was built the amount oflivable square footage and the types of energy used After lling out the appropriate slots on that page click ave Answers This will take you to another a e that has links to various aspects about a home such as water heater lighting etc The calculator will also assign you a Session ID number which you should write down on the activity sheet the number is found next to the Calculate button Clicking on each on of these factor links will allow you to personalize the information about your home such as what type of air conditioner you have and what are your temperature settings After you have visited a link the page will place a blue dot by that linkto tell you that you have already filled in that information When you are all done with the factors click the Calculate button The serverwill then take some time usually 20 seconds to calculate the usage in your home and to present the information back to you in the form of a bar graph with dollar amounts for using the different components in your home Information about the amount of electrical energy used can be received by clicking on the See Greenhouse Gas Emissions and Energy Consumption button This will open a new window that contains the information Use this information to fill in the activity sheet below Now that we have the approximate electrical energy usage per year we are prepared to investigate the economics of using solar or wind energy in your present location Let us start with solar energy Use the annual solar radiation map from the National Renewable Energy Labs to find out the average amount of solar energy that strikes a lm2 solar panel at your current location Multiply this value by 365 days in order to calculate the amount of energy that is striking the surface in a year and enter this value on the activity sheet as the ASE Since the best commercial solar panels are only about 1820 efficient this number needs to be divided by 5 in order to calculate the approximate amount of energy produced by a lm2 solar panel per year in your area lfthis number is then divided into the total amount of electrical energy needed for you home you will have estimated the area of solar panels that you need to meet your electrical needs for the year Using current price estimates either find this data yourself or ask your instructor for solar panels then allows you to calculate the price of putting in solar panels Afterfinishing filling in this data answer the questions on the activity sheet On the last question you will be asked to revisit the calculator to make changes in your home References Home Energy Savings Calculator httpwwwhomeenergysaverlblgov Solar Radiation Map ht ln39lwww nrel 39 39 csp us annual mav7004 inn PHSC 1014 Activity Sheet Solar Energy Name Session ID number Average Solar Energy ASE at your location kwhrm2 Average Solar Panel Output ASPO at your location ASE5 kwhrm2 Size of solar panel needed for your location Total Kwhr from tableASPO m Average cost of lm2 commercial solar panel Estimated cost of home solar system Size of solar panel X average cost 1 The average solar panel system should last about 2530 years before it needs to be replaced If you were to keep paying the same cost for electricity that you do now how does the total cost of a solar system compare to what you will pay over that time span 2 As oil prices continue to increase it is expected that all energy costs will go up lfthis happens you can expect to pay more for electricity in the future lfthe cost were to double over the next decade how would this affect your answer to question 1 3 If you used less electricity you could put in a smaller solar system thereby reducing your total cost Go backto the calculator remember your Session ID number and make the following changes a increase summer thermostat settings by 2 degrees b decrease winter thermostat settings by 2 degrees c reduce dryer loads to 0 use a clothesline and d reduce dishwasher loads to 0 wash dishes by hand All of these changes will cost you no money By how much did this decrease the amount of electricity you used By how much did the size of your solar system decrease Is your system more reasonable now Chapter One Energy Basics Definition nergy is all around us It is in the food we eat the gasoline we put in our cars and sunlight that strikes our face But what exactly is energy We use the term often as in quotI just don39t have any energy todayquot Since we are all so familiar with the word energy one would think that we would all be experts on the subject However our use of the word quotenergyquot in our everyday lives is somewhat different from what the word means in a scientific sense For the purposes of this class we are going to define energy as quotthe ability to do workquot Of course this definition is not as useful as it would appear since the word quotworkquot in this definition also has little to do with our ever day usage W do n mean 39ob taskquot for word Instea we mean quotthe transfer of energ to an object by applying a force through a distancequot Once again we find a definition that is lacking as we must now define what we mean by a force Therefore before we go forth with our definition of energy we will need to backtrack a bit and review some terminology from physics Physics Primer Position Velocity and Acceleration 5m4 1115 111 The eas1est place to start our rev1ew of terms Is with position In both physics and our everyday direction Figure 1 shows a diagram ofa point that is 4 meters to the east and 5 meters to the north of the origin This would be a valid way of stating the position of the point although there are others For instance you could say that it is 64 meters from the origin at an Flg 1 Posmon d39agmm angle of 51 degrees above east Knowing the position of an object is great as long as the object is not moving If it is moving then we will need to know something about how it is moving in order to locate at times in the future One thin that we might wish to know is the rate at which the object is changing its position or its velocity Mathematically we would write this as velocity v change in positionchange in time ArAt Equn 11 where r is the vector that defines the position of the object and t is the time The unit of velocity in the 51 system is meterssecond or ms Since the position is a vector quantity vectors are designated either with a small arrow over the quantity or by using bold print the velocity is also a vector quantity Many times people will say that velocity is the speed of an object with direction This is in fact only true in a very special circumstance Speed is defined as the distance travelled divided by the amount of time to travel or speed distance travelled At Equn 12 The reason why this is not the same as the magnitude of the vector quantity velocity is that that the distance travelled can be greater than the change in position To illustrate consider the Daytona 500 an automobile race in which cars travel 500 miles The average speed of a car in this race is 500 miles divided by the amount of time that it takes to complete the race If it were to take 3 hours to complete the race then the average speed would be speed 500 miles3 hours 167 mileshour Since the cars finish the race where they start it the change in position over that same 3 hours is 0 miles Thus the average velocity of a car in this race is 0 mileshour The only time that one is assured that the speed is the magnitude of the velocity is when instantaneous speeds and velocities are under consideration ie when At is an infinitesimally small amount of time As with position knowing the velocity is great as long as the velocity is not changing If it is then one would need to know the rate at which the velocity is changing in order to determine its velocity at some point in the future which will be used to determine position The rate at which velocity changes is known as the acceleration and is given by acceleration a AvAt Equn 13 The unit of acceleration in the 51 system is meterssecondsecond or msz Again since the velocity is a vector quantity the acceleration is also one Some people call negative accelerations decelerations although it is still an acceleration Forces As you might guess the acceleration of an object can change which would cause one concerned with its motion to be motivated to compute the rate of change of the acceleration there is such a thing it is called the jerk The fact is that you could continue defining the rates of change in an endless stream if you are really concerned about the motion of an object However we stop at acceleration since it is related to a much more useful term force As discovered by Isaac Newton the acceleration of an object is related directly to the net force on an object More precisely he found that Fnet ma Equn 14 where m is the mass of an object The unit of mass in the 51 system is kilograms which leads to forces being measured in kilogram msz or kg m 52 This is known as a Newton which is represented by a capital N In the English system of units forces are measured in pounds lbs whereas the unit of mass is known as the slug Unfortunately many books confuse this matter by stating conversions between pounds and kilograms which is technically incorrect since pounds are force and kilograms are mass What is assumed in this conversion is that the object is at the Earth s surface where gravity is providing a force that causes objects to accelerate at 98 m 52 This equation is just one part of a set of laws that have come to be known as Newton s Laws of Motion even though Newton only discovered the last two of them Galileo is credited with discovering the first one These laws are normally stated as 1 An object at rest or in a state of constant motion will continue in that state unless acted upon by an unbalanced force 2 Fnet ma 3 For every force there is an equal and opposite reaction force These laws are very useful tools as they allow us to relate measurable quantities acceleration to dynamical variables which can be used for all manner of calculation and observation They tell us that anytime we see an object accelerating we know that there is a net force acting on it whether we see the any other evidence of that force or not For instance if we detect a faraway star moving in a circle then we know that something is acting upon the star to make it do so By calculating its acceleration we can determine the magnitude and direction of the force which will allow us to search for the source force Because of our everyday experiences though we often misunderstand forces that occur here on Earth For instance if you push a large box across the floor at a constant speed Newton s Laws state that there is no net force on the box However you know that you are applying a force as you can feel it in your muscles and bones What is happening is that as you are applying a force to the box friction is applying an equal and opposite force to keep the box from accelerating When you initially began to push the box you were able to push harder than friction and thereby accelerate the box to some velocity At some point either the force of friction increased to match your force or you began to push with less force so that the two became equal The situation becomes even more misunderstood when we consider a box so large that you cannot move it In this case you are applying a force to the box that is equal to the force that friction is applying to the box and there is no net movement Often folks will cite Newton s Third Law Action Reaction as the reason for the lack of movement However this is wrong The reaction force to you pushing on the box is the box pushing on you not the force of friction of the floor on the box Even when the box is moving across the floor at a constant velocity the reaction force of the box on you is still there A better way to visualize the Action Reaction 239 Force Law is to consider two people without skates in the middle of a very slippery ice rink If either of the two attempts to walk off the ice they will find that there is nothing to push on meaning that they will not experience the reaction force that will propel them off of the ice Each will find that they can get i off of the ice if they push off of the other However Fig 2 Two people on ice in doing so they will notice that the other person is also propelled off of the ice This is because in pushing on the other person the other person was actually pushing back on them Forces and Work Now that we know what a force is we are ready to get back to our definition of work We said at the beginning of this chapter that work is the transfer of energy by applying a force through a distance If the force is unchanging then we can write the work as W F d Equn 15 where F is the applied force and d is the distance through which the force is applied If the force is changing we can still use the above equation but we must break up the distance traveled into small segments over which the force does not change that much calculate the work over each small segment and then add up all of the work from each segment The units of work in the system are newton meter which is known as a joule after James Joule the scientist that discovered the First Law of Thermodynamics Before proceeding any further we need to point out that the force used in equation Sis only that portion of the force that is parallel to the path of travel Figure 3 shows a diagram of two different boxes that are being pushed across a floor with the same force F In the first case box Flg 3 Boxes bemg WSth 0 001quot with the fish on it the force is parallel to the surface of the floor whereas the second box box with tree is being pushed at an angle 6 with respect to the surface of the floor If both boxes move the same distance d then the work done on the first box is F d while the work done on the second box is less This is because it is only that portion of the force that is parallel to the surface of the floor F times the cosine of e or F cos 6 that is doing wor 39 moving it across the floor Some portion of the force F sin e is going towards pushing the box into the ground and is doing nothing more than increasing the force of friction on the box In the extreme case the angle 6 would be 90 degrees pointing straight down in which no work would be done as the box would not move parallel to the surface of the floor This can also be applied when you lift up the box and carry it across the room While you are lifting the box you are applying the force in the direction that the box is moving and are thus doing work on the box However as you carry the box across the room the force that you are applying to hold the box up is not doing any work on the box even though the box is moving and a force is being applied to it Since the force that holds the box up is perpendicular to the direction of motion it does no work on t e ox he on y work you are doing on the box is the sma amount of force that you are applying to keep it moving across the room times the distance you move it Energy Relationship Between Work and Energy 0 far we have been looking at the world from the standpoint of doing work on objects in order to transfer energy to them This standpoint is perfectly valid However you might remember that we defined energy as the ability to do work Thus it would seem that there is an alternative view that looks at the world from the standpoint of expending energy in an effort to perform work on other objects To get a better understanding of this view it might help if we discuss a c ncr example of energy To do this we must first define two different types of energy kinetic energy and potential energy Kinetic energy is the energy that an object has because it is moving A car traveling down the highway at 50 miles per hour has kinetic energy as does a baseball that is thrown at 100 miles per hour By slamming into other objects they will be able to do work since their momentum will cause them to apply a force through a distance as they collide How much kinetic energy they have is determined by the formula Kinetic energy KE 12 m v2 Equn 16 Since the car has so much more mass than the baseball it will have much more kinetic energy even though it is moving at half of the velocity Anyone who has been hit by both a car and a baseball and survived can attest to this Potential energy is the energy that an object has because there is a force operating on it in a direction in which it is able to move A book perched on the top of a shelf has gravitational potential energy since gravity is pulling it toward the ground and there is a distance between the shelf and the floor through which it can move Likewise a uranium238 nucleus has nuclear potential energy since the protons and neutrons can move under the influence of the forces acting on them strong and weak nuclear forces to be more tightly bound Since the forces involved in the potential energy will change depending upon the object and situation there is no way to write one formula that will cover all types of potential energy However we can readily derive the formula for a given object by simply considering the amount of work that is required to move the object from one place to another As an example let us consider moving an object near the surface of the Earth In 1684 Isaac Newton wrote that the force of gravity between two objects of mass m1 and m2 that are separated by a distance r is given by F G m1 m2r2 Equn 17 In this equation G is a universal constant Since the E In h Earth is so large radius 6300 km the difference in g force between an object that is at the surface and one that is a kilometer above the surface is less than 04 This means that for all intents and purposes the force of gravity near the surface of the Earth on an object is a h constant By plugging in the appropriate values for G mam and r we get that the force is F m 98 ms2 mg Equn 18 Now let us consider an object that is a height h above the ground fig 4 In order to get the object to F mg the height h we had to pick the object up from the ground and lift it to h This would require that we offset Flg 4 Llfted box the force ofgravity ie we have to lift it with a minimum force of F mg From Equation 5 this means that we had to do an amount of work equal to W Fd mgh mgh Equn 19 Since this is the amount of work that was required to lift it to h then the amount of potential energy that the object acquired is this Thus the gravitational potential energy of the object is mgh Since we have not designated any object mass or height this equation PE mgh is true for any object near the surface of the Earth This type of procedure can be done for any system that stores potential energy For forces that vary with distance calculus must be used to sum up all 0 the little work segments as we discussed previou given by kx w ere k is a constant an x is the distance the sp ng Is compressed or extended from equilibrium This results in a potential energy of PE 12 kx2 The force between two charged particles q1 and q2 is K 1q2 r2 where K is a constant q1 and q2 are the charges magnitude and r is the distance between them This system has a potential energy given by PE K qlqu Transferring Energy Both kinetic and potential energy are types of mechanical classified into these two categories Electricity is a form of kinetic energy since it is the movement of the electrons that is used for all of the Chemical energy such as that found in food or gasoline is a form potential energy The energy that is released when chemical energy is use comes from the forces between atoms and molecules that are allowed to operate Table 1 has examples of energy with designations as to type Table 1 Different energies and their classi cation Because energy can be used to do work on another object it can be transferred from one form E mgh to another Let us once again look at the example of the object that is a height h above the floor When it is at a height h we say that it has potential energy of mgh If we release the object gravity is allowed to act upon it and it accelerates Its acceleration means that it is acquiring kinetic energy 12 mv2 However as it accelerat s h Initial energy as een co which the object will give to the Earth when it strikes it Fig 5 Diagram of falling box Since there is no other energy input or output assuming negligible wind resistance into the situation we know that all of the kinetic energy at the moment of impact is equal to all of the potential energy initially Thus mghmai 12 m Vina Since both sides of this equation are linear in the mass of the object we can cancel them and solve for the velocity Doing so yields V nalzgh12 This equation shows that the final velocity of the object only depends upon the initial height of the object something that Galileo discovered back in the 160039s by dropping cannon balls of different size Simple Machines This type of situation in which there is no net energy input or output is an example of the conservation of energy principle Energy will be transferred from one form to another but it will not degrade or increase This is the basis for a classification of simple devices known as simple machines These devices allow one to move large objects with small forces by taking advantage of the fact that energy is not lost In essence they are force multipliers The most common sim le machines are the lever the fulcrum the wheel and axle the block and tackle and the inclined plane Figure 6 shows a diagram of an inclined plane This device is used to lift object above the ground As we have already seen above one can lift an the inclined plane to lift the object this person will only have to supply a force equal to that component of gravity that is along the path of the plane Using simple geometry we can see that this Fig 6 Box on anincline plane component is given by mg sin 6 Since sin e hL this means that the force that must be supplied to push the object up the plane is F mghL which is less than mg However the amount of work that must by done is the same as above because the force must be applied over a longer distance L W FL mghL L mgh Thus the incline plane allows for a smaller force to be applied over a longer distance resulting in the same amount of work done but a larger object being moved The same thing holds true for all other simple machines Power Simple machines are sometimes used to make people think that they are getting something for nothing you get a greater force but it requires that you apply the force longer In a similar fashion power is sometimes used to do the same thing Power is the rate at which work is done or energy is expended depending upon the situation In other words P AEAt Equn 110 The SI unit for power is the watt which is equal to a joule per second As an example a 100 W lightbulb is using 100 joules of energy every second in order to emit light The confusion comes into play because power and energy are sometimes used interchangeably For instance an advertiser can claim that a product will save consumers money because it uses very low power While our appliances are rated by power we are charged for the energy we use usually in units of kilowatt hours It makes sense to charge this way since it is the energy that determines how much total work gets done This is not to say that one can neglect power In particular the electric company has to be very concerned with power When many people use appliances at the same time ex air conditioners during a hot summer a tremendous amount of energy must be supplied in a very short amount of time Even though the electric company might have a lot of energy on hand ex large stacks of coal unless they can supply the energy fast enough a brownout or blackout will ensue For this reason most electric plants are rated by the maximum power that they can output Knowing this relationship between power and energy can be very useful to you It allows you to determine how much energy you use when you turn on appliances AE P At For example if you leave a 5000 W stove on for 2 hours then you have used AE 5000 W2 hr 10000 Whr 10 kWhr Multiplying this usage by the rate that your electric company charges you will tell how much money it cost for this operation Most companies charge somewhere between 05 20kWhr This would mean that the stove operation above costs between 50 200 Electricity Generators and Motors Charge Some of the most important forms of energy transfer are those from kinetic energy to electrical and from electrical to kinetic energy Over 13 of all of the energy consumed in the US goes toward the creation of electricity Electricity runs almost every appliance in our homes from computers to stereos to refrigerators and air conditioners Some of these appliances like refrigerators heaters and air conditioners contain motors which convert the electricity back to kinetic energy In order to understand how this all takes place we need to review a little bit of the subject of electricity and magnetism Benjamin Franklin is one of the most famous American statesmen He is hailed throughout most history classrooms in the US as a great politician As a sidelight historians will tell tales of his other adventures as a journalist and inventor In particular they will bring forth images of him flying kites in a storm with a key attached to it to attract lightning What rarely if ever gets told is that the reason why Benjamin Franklin was able to become a great statesman was ecause o his ame and renown a a journalist and a scientist It is not that Franklin was an inventor that dabbled in science he was one of the foremost scientists of his time It is he who developed the entire notion of all neutral matter eing composed of particles of opposite charge in e ual numbers He developed the notation of positive and negative charges His work with lightning led him to the discovery that air was much more likely to reakdown in the presence ofa s arp charged conductor and ence development of the lightning rod design that we still use today For all of his work in science he was made the only foreign member of the French Academy of Science which was the premier science organization of its ime This small soapbox excursion into history is an indirect way of saying that all matter has a property that is nown as c arge energy levels ound in our everyday life matter is made u of three different particles which have three different charges Neutrons which normally exist in the nucleus of the atom are neutrally charged and ave a mass of a omic mass uni amu 1 x 103927 k Protons which also normally exist in the nucleus of the atom are positively charge and have a mass of 1 amu The last particle is an electron which is negatively charged exists outside of the nucleus and is rather light about 001 amu While like charges re el positive repels positive negative repels negative and un 39ke charges attract positive attracts negative neutral particles are neither attracted nor repelled by t e other two he at rac ion etween positive and nega ive accounts for why electrons are bound to protons in the atom The neutrons are bound to protons by two other forces the strong and weak nuclear forces which we will discuss in a later chapter on nuclear energy While static electrical charges are able to repel or attract other charges they are not able to repel or attract magnets This point cannot be stressed strongly enough as many people confuse static electricity with static magnetism There are two good reasons for this For one magnets ave a north and south pole just like charges can be either positive or negative Furthermore north poles repel north poles south poles repel south north poles attract south poles w ich 39s analogous to charged particles While analogous in behavior static electrical charges will not interact with static magnets The other reason for confusion is because moving charges and moving magnets can generate magnetic and electrical fields respectively The discovery of this fact goes back to Hans Oersted in 1820 who found that a constant electrical current generate a magnetic field This field was found to run in a circular pattern around the wire with the current as the center of the circle When Oersted g7 Oersted s experiment placed static magnets around the wire he found the presence of a current in the wire created a force that pushed on the magnets and rearranged them Thus he found that a moving charge can have a force on a static magnet Ajudicious application of Newton s Third Law allows for the reverse of this statement a static magnet would have a force on a moving charge Thus if a charged particle is moving past a static magnet at a constant velocity there will be a force on the particle Note Due to t e manner b the th i ertial constant velocity reference frames equi t ans th thing would magnet were i a on n Fig 8 Chargedpanicle velocity in the opposim direction past the cha g d moving between magnets rti if the ch rged i one moving ence oving g t cre tes ic c ar d particle The only way that this could occur is if the moving magnet is creating an electric field So to summarize static charge particles only create electric fields and static magnets only create magnetic elds Moving charged particles create both fields as do moving magne 439 led to was the 39 39 etism are just two different manifestations of the same force and that they are intimamly tied mgether We could spend an entire semester discussing these particles and their properties However that is notour intent here what is of particular inmrest to us is making a stream of charged particles known as a current It is this stream that carries energy from one place to another what we will now focus on is how these u rents are created and how they can be used to create motion Conducting Paths here are two requirements for an electric current a potential difference an a conducting path The conducting path part of this requirement is easy to supply All that is required is some material that can pass charged particles For most cases metals fulfil this job quite well All atoms have electrons in orbit about the nucleus at various energy levels Electrons can be liberated from atoms if they a orb an 39 r y I e e a lot o free electrons in metals thatare able to move in response to a potential difference of course there are other materials thatcan carry an electrical current although not as well A measure of how well a material carries current is given by its resis 39ty The better a substance conducts electricity the lower the resistivity will M ood conductors like silver copper and aluminum 39 39 39 on the order of 1039 ohm meters while poorer oonductors like carbon 0 meters silicon 1 ohm meters and glass 10 ohm meters have much higher values The resi u39viLy id 4 L a A A with values usually getting lower as the temperature of the substance is lowered o g For a smaH c ass of mate a s there are temperatures at thch the resTsthtv goes to zero At these temperatures these dewces are superconductors thch me s that thev wTH not transfer anv of the e ec mca energv to heat a rreht thro gh them Creatmg mate a s that are superconductors at room temperature Ts the uTtTmate goaT tor some condensed matter researchers as e ec mc hnes currehtw ose about 10 of 5 of ther energv to resTstahce osses L We shoud pomt out that the resTstthv shoud not be confused thh resistance aTthough the two are re ated The resTsthtv depends upon the mate a and t5 temperature the resTstahoe Ts the measure of Tmpedahce of an actua WH e d t depends upon the resTsthtv ahd dTmehsTohs or the WH e 1h partTcuTar the resTstahce S gweh by the formu a g 9 ow Fig 9 Wire diagram R p LA Equn 111 where p S the resTsthty L S the ength or the WW6 and A S the cross sectTohaT area or the WH e The umt tor resTstahce 5 ohms Q m the 51 svstem The resTstahce or a WH e S verv mportant as we wTH decuss ater Potential Differences otentwa dwfference can be created Sun Bnduc b t d d H dt outthrough the egatT poe of the bat erv At the other Fig 10 Galvamw l poTe the e ectrons combme thh other Tohs m soutToh to pate the meta to the poe ah thus comp ete the CH CLHt gure 10 shows dTagram or such a erv e charactehstTc or battehes S theTr portabmtv Our modem w v or Me depends on t from the 12 v batterv m our car to the smaH battehes m our ceH phones and aptops Wh e thev are a potehtTaT source battehes are reaHv Just storage dewces tor h can be connected to one or a number or k hetTc energv sourc s steam turbme WmmeHS Waterwhees etc to prowde arge quahtmes or e ecmca energv The basis behind the operation ot a generator is the abilitv ot rnoving charged partides 1 to o n a on 3U 8 i m rnagne icti ld thev experlel lce a torc ti erpendic lar to their i This torce causes l th ire thus c ati e rnanv other possible rr t oontigurations tor a generator but thev operate on the same basic principle s ong as the axle is oonnected to a kll letlc energv source the generator will produce an electrical current Fig 11 Generator diagram The tvpe ot current that is produced bv a generator depends upon the contiguration ot the wires and how are attadned to the outside ot the generator I ca r m haltin the other direction This is an alternating current or a c potential Electrical Energy and Power Bot hese mrrents carrv kll letlc energv through the wire The amount ot energv that it carries depends upon how rnuc c arge ows through the wire and the potential ditterence through which the charge ows in much the same wav that the energv ot a dropped obiect near the surtace ot the depended upon the mass ot the obiect and the height through which it tell Mathematicallv this becomes AE Aq v Equn 112 where Aq is the amount of charge and is the electric potential In the SI svstem q measured in ooulombs1c 16 gtlt10 9 proton charges and v is measured in volts while this equation is usetul trorn the standpoint ot describing electrical ergv it is not ot rnuch ractical use tor our evervdav lite The reason tor this is bv their power rating and not their energv usage s an example look at a light bulb Somewhere on the bulb there will be printed the wattage or power rating ot the b This is calculated bv knowll lg the voltage ot the appliance and the amount ot current that it will draw U E p l v Equn 113 in Equation 13 l stands tor the current entering the appliance and is measured in am eres 1 am 1coulornbsecond in the S s stern A long as two ot the variables in the equation are known the third can be calculated For instance a 500 watt microwave oven is plugged into a 110 outlet This means that it draws an amount of mrrel39lt equal to PVSOOW110 45A This power rating is used to calculate the amount of energy that an appliance expends as we discussed earlier Equation 110 This power used by the appliance is not the only power that needs to be supplied to the system As we discussed in the Conducting Path section all wires between the potential source and the appliance have resistance This resistance will convert some of the electrical energy to heat which depletes the amount of energy that gets to the appliance The rate at which the resistance converts energy is given by P I2 R Equn 114 If the wire going into the microwave has a resistance of 1 Q a fairly small value then the power that is being lost to heat in the system is P45A21220W This example shows one of the problems with our current system of supplying electricity to homes from centralized power plants The electricity must flow over long distances from the plants to the various homes through wires that have resistances In doing so about 10 of the total energy originally created is lost to resistance Energy Use History From the earliest days humankind has recognized the need to use energy to condition the environment around it Wood was needed to heat homes and to cook food Beasts of burden were needed to plow fields and to provide transportation When either of these commodities became scarce hardship prevailed and solutions were sought In ancient Rome for example the lack of available firewood led to the passing of laws that made it illegal to build a house or structure that would block another person39s home from getting sunlight as this was the primary method of heating homes without fire In the 20th century fossil fuels oil in particular reigned supreme as the energy of choice The ubiquitous nature of this type of fuel created historically low prices for energy This led to a substantial increase in the number of mechanized tools used by the average citizen By the year 2000 the US had a population of about 283 million people that were driving over 200 million passenger vehicles1 Almost every home in America has a television some type of range or stove and a refrigerator About 34 of all households have their own washer dryer and air conditioner2 Of course this cheap price does not come without some political and economic consequences Energy and oil in particular have played a very important role in the economy and politics throughout the last 150 years affecting everything from the entry of US into World War II to the rampant inflation of the 197039s to the current de stabilized situation in the Middle East Energy Use in the US This modern dependence on many appliances of convenience requires a lot of energy Our current energy per capita use is over 340 million BTU39s of energy3 Put another way this means that the average US citizen would be responsible for using almost 60 barrels of crude oil each year if all of the energy used in America came from oil The only other country in the Western World that was even close to this is Canada which has almost the same amount of usage Most of the Western world uses 200 million BTU39s of energy or less Although we make up only about 5 of the world39s population we account for almost 25 of all of its energy consumption In comparison many Third World countries such as Ethiopia use less than 1 million BTU39s per person The majority of this energy 86 is supplied by fossil fuels Crude oil accounts for the largest share of this 38 followed quickly by coal 22 and natural gas 22 The remaining energy comes mostly from nuclear 8 and renewable sources like hydroelectric solar and wind 6 Contrary to common belief most of this energy is produced domestically The only energy source which we are forced to import is crude oil of which we can currently supply only about 45 of our need Of the energy used in the US about 38 of it is used for industrial processes mining milling etc 36 of it is used to power homes and offices and 28 of it is used for transportation While most of us cannot directly affect the amount of energy used for industrial processes we can do something about our residential and transportation energy use The figures above mean that about 101 million Btu39s are used each year just to run our households this does not include the energy that was lost in producing and transporting this energy which accounts for an additional 71 million Btu39s The majority of this energy use is to heat and cool our homes 55 References 1 Bureau of Transportation Statistics htt wwwbts ov ublications national trans ortation statistics 2002 html table 01 11htm 2 A Look At Residential Energy Consumption DOEEIA 063297 November 1999 Energy Information Administration Washington DC 3 httpWWWeiadoegovemeuaertxtzptb0101html December 22 2003 4 http1wwweiadoegovzpublstatedatapdfuspdf December 22 2003 John M Pratte
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