SNC1L Unit 3 Electrical Circuits

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1 SNC1L Unit 3 Electrical Circuits

2 SNC1L Science Unit 3 - Introduction Introduction Electricity is an energy source that we encounter every day. We are very familiar with what electrical energy can do, but we may not be as familiar with what electrical energy is. In this unit, you will learn how electrical energy can be transformed into other forms of energy. You will also learn how electric circuits can be designed and built, and how electricity can be used in the home, workplace and community. This unit will attempt to further develop your previously perceived ideas of electricity, and build on your those ideas so that you will further develop an understanding of what electrical energy is and not just what it can do. The three themes of in this unit are (1) describing and investigating electricity; (2) designing and building electric circuits that perform specific functions; and (3) analyzing the practical uses of electricity in everyday life, and its impact on the environment. Copyright Durham Continuing Education, 2005 Page 2 of 66

3 SNC1L Science Unit 3 - Introduction Overall Expectations After completing this unit, you will be able to: Describe the characteristics of electrical circuits Investigate simple electrical circuits, using safe practices Analyse the practical uses of electrical circuits and their impact on daily life Materials Required In this unit, you will need the following material Balloon Confetti Plastic comb Cotton or wool sweater 6 Volt Battery 1.5 Volt Battery 2 small torch light bulbs 4 electrical wires with alligator clips 2 funnels of different size Cotton balls Supply of water 2 plastic containers Copyright Durham Continuing Education, 2005 Page 3 of 66

4 SNC1L Lesson 11 Static Electricity

5 SNC1L Science Unit 3 Lesson 11 Introduction Everything around you, including the storm clouds in the sky, contains electric charges. When you rub a balloon against your hair, electric charges are not created, they simply move. Objects become charged when electrons move from one object to another. In fact, all the atoms in matter always contain electric charges. But you aren t always aware of the charges in the balloon or your hair until you make them move from their normal positions. When they are forced to move, as they are when objects of different materials are rubbed together, we say that the materials have become charged with electricity. Some objects remain very briefly, while others can stay for a very long time period, weeks, or even months! Rubbing two objects together, like your feet on a nylon rug, can cause a build up of charge at the point of contact. The electric charge stays where the rubbing happened on the charged objects, therefore the charge remains static. As you know from your own experience, clothing such as nylon shirts and woollen sweaters, often become charged with electricity when the articles rub against one another in the dryer. This build up of charges has come to be known as Static Electricity. Static means not moving. The study of static charge is called electrostatics. What You Will Learn After completing this lesson you will be able to: Demonstrate an understanding that electrical energy can be converted into other forms of usable energy (eg, heat, light, motion) Copyright Durham Continuing Education, 2005 Page 5 of 66

6 SNC1L Science Unit 3 Lesson 11 What is Matter made of? Atoms and Types of Charges As you learned in Unit 2, matter is all around you. This book is matter. Water is matter. So is air. You are matter. In fact, everything you can see (and much of what you cannot see) is matter. Matter is anything that has weight and takes up space. Matter comes in three states: solid, liquid, and gas. Solid, liquid and gas are the three states of matter. All matter is made up of atoms. Atoms are called the building blocks of matter. Atoms are unbelievably small. A tiny bit of matter may have billions, even trillions, of atoms. The period at the end of this sentence, for example, has more atoms than you can count in a lifetime. Can you imagine how many atoms there are in all matter? Don t try! The number is too enormous. It is impossible to describe. Even with the enormous number of atoms n the world, there are only 113 (maybe even more because they are constantly being discovered) different kinds of atoms known. The elements from 104 on do not exist in the natural world. This means they have been created in atomic laboratories. They are very difficult to study because they exist for only a small fraction of a second. Some matter is made up of only one kind of atom. Most matter however, is made up of two or more different kinds of atoms linked together. Matter made up of only one kind of atom is called an element. There are 113 kinds of elements. That s one element for each kind of atom. You know the names of many elements. Oxygen, hydrogen, iron and gold are all elements. Matter that is made up of different kinds of atoms linked together is called a compound. There are millions of compounds. Almost everything you see is a compound. Water, wood, plastics even your skin and blood are compounds. The Atom In order to explain the action of electric charges we must have an idea of what matter is made of. All matter is made of very small particles called atoms. Each atom has three important types of particles; protons, neutrons and electrons. Protons and neutrons exist close together inside the nucleus of the atom. The force that holds the nucleus together is so strong that the atom does not easily lose protons. Around the nucleus travel tiny particles called electrons. They are the only particles in an atom that can move. The forces Copyright Durham Continuing Education, 2005 Page 6 of 66

7 SNC1L Science Unit 3 Lesson 11 holding electrons in place are relatively weak. Thus, an atom can gain or lose electrons relatively easily. Refer to the following figure to see the location of these particles. All atoms of one element, such as oxygen, are the same. However, different elements have atoms with different numbers of protons, neutrons and electrons. For instance an oxygen atom has a different number of protons, neutrons and electrons than a helium atom. Electrons always carry the same type of charge. The electron is negatively charged. Protons carry the opposite charge, they are positively charged. The size of the charge on one electron equals the size of the charge on one proton, only the sign is different. A neutron has a neutral charge, in other words, no charge at all. These basic ideas will be used to explain many events observed in the topic of electricity. What is Static Electricity? Do you ever have trouble getting your hair to stay down after you ve brushed it? Do your clothes crackle when you remove them from the dryer? Do you ever get a shock from touching a door knob? If you answered yes to any of these questions, then you are already familiar with static electricity. The cause of these strange occurrences is static electricity. Static means not moving. Static electricity is often created by rubbing together of different materials. This phenomenon is caused by the unequal numbers of protons and electrons on an object. As you know when the number of protons and electrons are equal in an atom the atom is considered to be neutral. The positive and the negative charges balance each other out. Then the whole atom has no charge. Sometimes, the positive and the negative charges are not equal. Then the atom is not neutral. The atom has a positive charge if it has more positive charges (ex. more protons). The atom has a negative charge if it has more negative charges (ex. more electrons). Matter that has charged atoms has static electricity. Copyright Durham Continuing Education, 2005 Page 7 of 66

8 SNC1L Science Unit 3 Lesson 11 Some static electricity is not the kind of electricity that we use for light bulbs, toasters and appliances. Support Question (These questions are NOT to be submitted for evaluation!) 1. Try this activity! Rub an inflated balloon against your hair, then place the balloon against the wall. What happens to the balloon? Explain your observations. 2. Try this activity! Rub a plastic comb on a piece of wool sweater, or cotton sweater, bring the comb near some very small pieces of paper confetti. What do you observe? Explain your observations. 3. Try this activity! Rub a plastic comb with a piece of wool sweater, or cotton sweater. Then bring the plastic comb close to, but NOT touching, a fine stream of water from the kitchen sink. What happens to the stream of water? Explain your observation. 4. Try this activity! Rub your feet (make sure that you are wearing socks) across the carpet. Then touch a metal doorknob. What happens? Explain your observation. Transferring Electric Charge Charging by Friction When the atoms of two different materials are brought into close contact, electrons may move from one to the other. You can see the effect of this electron movement when you comb your hair. If the material your comb is made of has a stronger attraction for electrons than your hair, your comb will take electrons from your hair. This is because electric charges can be transferred by a rubbing action or friction. Charging by friction causes many of the effects produced by static electricity. Large amounts of electric charge build up on clothes in a dryer because the tumbling motion is a kind of rubbing action. Copyright Durham Continuing Education, 2005 Page 8 of 66

9 SNC1L Science Unit 3 Lesson 11 The activities you tried, such as rubbing the balloon against your hair, and watching it stick to the wall as a result and rubbing your feet across the carpet, touching a metal doorknob which resulted in getting a shock, were all examples of charging by friction. Electrostatic Series You can use a list called the electrostatic series to determine the kind of electric charge produced on each substance when any two substances on the list are rubbed together. Table 1 Acetate Glass Wool Cat s fur, human hair Calcium, magnesium, lead Silk Aluminum, zinc Cotton Wax Ebonite Plastic Carbon, copper, nickel Rubber Sulphur Platinum, gold The Electrostatic Series Weak hold on Electrons (becoming Positive) Strong hold on Electrons (becoming Negative) When two substances are rubbed together, the substance nearer the top of the list (for example acetate) tends to lose electrons and become positively charged, while the substance nearer the bottom of the list (for example silk) tends to gain those same electrons and become negatively charged. Copyright Durham Continuing Education, 2005 Page 9 of 66

10 SNC1L Science Unit 3 Lesson 11 Using the Electrostatic Series When this first object Is rubbed with The second object Glass Rubbed with Rubber Hair Rubbed with Acetate Rubber Rubbed with Sulphur The first object becomes Glass becomes Positively Charged (+) Hair becomes Negatively charged (-) Rubber becomes Positively charged (+) The second object becomes Rubber becomes Negatively Charged (-) Acetate becomes Positively Charged (+) Sulphur becomes Negatively Charged (-) Consider the following example; this polythene or plastic rod is being charged by friction as a result of rubbing against a cloth cotton material. The cloth material looses electrons to the plastic rod, therefore having more positively charged particles. The plastic rod ends up with more electrons than normal, therefore becoming negatively charge. The negative charges are transferred from the cloth to the plastic through the action of rubbing. Charging by Contact A single spark produced by a charge transferred by contact can cause dangerous fires and explosions. Safety precautions, such as wearing boots and shoes that do not produce sparks and the use of special clothing, are required in grain elevators, flour mills, coal mines, hospital operating theatres, and some parts of oil refineries. Planes and vehicles transporting flammable materials need to have special equipment installed to prevent or control sparks produced by static electricity. Transferring a charge by friction is difficult to avoid. Even if you are initially uncharged and walk carefully over a carpet, many electric charges are gradually transferred by the rubbing action of your shoes on the carpet fibres. But when charging by contact occurs, Copyright Durham Continuing Education, 2005 Page 10 of 66

11 SNC1L Science Unit 3 Lesson 11 one object is already electrically charged. The other object may or may not be charged as well. The important factor is that there must be a difference in the amount of charge already on the two objects. Before you touch the doorknob, you may be charged negatively, due to friction with the carpet. The doorknob is usually uncharged. When you touch it, some of the extra electrons on your body transfer to it. Thus the total electric charge on your body is shared between you and the doorknob, and the charge is transferred to the doorknob is also negative. The shock produced by this kind of charge transfer can be surprising and even painful. This is because the electric charges on your body are shared with doorknob very rapidly. In fact, usually your hand doesn t even touch the doorknob before the charges begin to transfer in the form of a spark. The electrons actually jump across the air gap between your hand and the knob just before you touch it, like a miniature lightning stroke. Copyright Durham Continuing Education, 2005 Page 11 of 66

12 SNC1L Science Unit 3 Lesson 11 Support Question (These questions are NOT to be submitted for evaluation!) Complete the following sentences by filling in the blanks: (remember you cannot write in this book, therefore you must rewrite the sentences in you notebook) 5. All matter is made up of tiny particles called. 6. At the centre of each atom is a nucleus, with two kinds of particles; the positively charged and the uncharged. Protons do not move from the nucleus when an atom becomes charged. 7. A cloud of negatively charged particles called surround the nucleus. 8. An electron has the same amount of charge as a, but the kind of charge is opposite. When atoms become charged, only the electrons move from atom to atom. 9. In some elements, such as copper, the nucleus has a weaker attraction to its electrons than in others, and electrons are able to move freely from to. 10. In each atom, the number of surrounding the nucleus equals the number of in the nucleus. A single atom is always electrically. 11. If a substance gains extra electrons, the overall charge on the substance will be. 12. If a substance looses electrons, the overall charge on the substance will be. Copyright Durham Continuing Education, 2005 Page 12 of 66

13 SNC1L Science Unit 3 Lesson 11 Law of Electric Charges Two objects with like charges, whether positive or negative, always repel one another. However, when a positively charged object is brought near a negatively charged object, they attract one another. This behaviour is referred to as the law of electric charges, which states: like charges repel one another, and unlike charges attract one another. To determine whether an object is charged and, if it is uncharged, whether the charge is positive or negative, you must observe the object being repelled by an object with known charge. Charged objects will attract both neutral objects and objects with unlike charges. On the other hand, charged objects will only repel objects with like charges. Discharging Electrically Charged Objects Every time you pump gasoline into the gas tank of a car, the flow of gas through the nozzle generates large amounts of static electricity. Think what would happen if a static spark jumped from the nozzle to the car. Static build up is an everyday occurrence. If there were not a way of continuously removing the charge as soon as it was produced, there could be serious consequences. If a charged object has all the excess electric charges removed, it is said to be discharged or neutralized. Several methods are used to discharge charged objects: grounding, discharging at a point and exposure to air. Grounding Grounding is the simplest way to discharge an object. Grounding involves connecting the object to Earth by means of a conductor, such as a metal wire connected to a metal rod buried in the ground. Copyright Durham Continuing Education, 2005 Page 13 of 66

14 SNC1L Science Unit 3 Lesson 11 When a charged object is connected or grounded to Earth, it shares its charge with the entire Earth. Earth is so large that it will remove all the excess charge from the object without problem. Discharging at a Point Not always are we able to connect objects to the ground. Take into consideration air travel; we couldn t possibly attach a plane to a ground wire. As aircraft travel through the air, they continuously build up huge amounts of static charge on the outside of the surface of the plane. The answer is to connect pointed metal rods that stick out from various areas of the plane, like the wings and tail. At the sharply curved point of a negatively charged rod, electrons repel one another so strongly that those right at the tip are actually pushed off the point in a continuous stream. This method of discharging is especially useful for the aircraft when flying through stormy weather. Exposure to Air Over a period of time, charged objects can be discharged by simply exposure to air. On a humid summer day, because of the number of water droplets in the air, the charge leaks away so quickly that many of the problems caused by static electricity are not noticeable. This explains why are clothes and hair are especially statically charged in the winter more so than in the summer. During the winter months, there is very little humidity in the air, therefore allowing for build up of static charges. Copyright Durham Continuing Education, 2005 Page 14 of 66

15 SNC1L Science Unit 3 Lesson 11 Key Questions #11 A) What could you rub aluminium with to give it a positive charge? To give it a negative charge? (use the electrostatic series) B) Give 2 examples of charging by friction that you have experienced at home. C) If a negatively charged object touches a door knob, what charge will it pass to the doorknob? (hint: charging by contact) D) Why does a spark occur when a person, who is negatively charged, touches a metal doorknob? What happens? E) Is the following statement true or false? Only the electrons leave the atom and travel back and forth through objects creating electric charge. F) Rewrite the law of electric charge. G) What are 2 of the 3 ways that you can neutralize or discharge an object? These questions must be submitted for evaluation! Copyright Durham Continuing Education, 2005 Page 15 of 66

16 SNC1L Lesson 12 Sources of Electricity

17 SNC1L Science Unit 3 Lesson 12 Introduction Think of all the ways you use electricity each day. You awake to an alarm, clock or radio, turn on an electric light, use an electric toothbrush, or make toast. You watch television, listen to CD s, use air conditioners. Just think about lights. Almost every place you go you find electrical lighting. Static charge may build up to the point that it causes a discharge in the form of spark jumping from your hand to a doorknob, or your clothes to stick together after being in the dryer. Whatever way it happens, electrical energy is transferred by the movement of electric charge. The movement or flow of electric charges from one place to another is called an electric current. Electric current is another source of electricity. In lesson 1, you learned about static electricity. In lesson 2, you will learn about other form of electricity and how they are created and used. What You Will Learn After completing this lesson you will be able to: Identify how household and workplace electrical devices operate by converting energy to another form (e.g., electrical energy to light energy in a bulb, flashlight; electrical energy to heat energy in a stove, electric heater and heat lamps) Copyright Durham Continuing Education, 2005 Page 17 of 66

18 SNC1L Science Unit 3 Lesson 12 Static Electricity and Current Electricity In both static and current electricity, electrons must move. In static electricity, electrons move from one object to another, where they tend to stay in place until they are discharged or neutralized. Current electricity involves the continuous flow of electrons through a specific type of material. Static electricity has only a few uses, whereas current electricity has many. The energy of the electrons that flow in current electricity can be changed into other forms of energy. Both static and current electricity can be dangerous, and both require caution to prevent injury or death. Static Electricity: The Facts Current Electricity: The Facts A build up of electrons The steady flow of electrons between objects or places Comes from far away on wire Stays in one place until it jumps to an object Needs a conductor, a substance that allows electrons to move easily through it Does not need a circuit Needs a closed circuit to flow The kind of electricity you feel after you drag your feet across a carpet and touch someone or something The kind of electricity that powers the appliances and heat in your home Lightning is static electricity on a more spectacular scale The kind of electricity in a batter What is Electric Current? The electricity that works all of your electrical appliances is called electric current. This is a flow of electrons. Electrons are the part of the atom that have the negative charge. Consider the following diagram, 3 atoms in a row, allowing for an electron to move from one atom to the next creating electric current. Electrons move along a path called a circuit. The current passing through a light bulb must flow through a controlled path called an electric circuit. Electric circuits are used to convert electrical energy into the other forms of energy we need. In order for the electrons to flow continuously, all aspects of the circuit must be connected to each other. This type of circuit is called a closed circuit. If a connection is broken, therefore stopping the flow of electrons, the circuit is considered open. Copyright Durham Continuing Education, 2005 Page 18 of 66

19 SNC1L Science Unit 3 Lesson 12 A study lamp, a flashlight, a toaster or blow dryer, and all types of electric circuits, are in many ways, very different. However, the electric circuits that operate all of the devices mentioned are essentially the same. They all have the same four basic parts found in the simple electric circuit shown below. These four parts are: 1. Source of Electrical Energy The source of electrical energy is what provides the circuit with electrons. The following are all examples of different types of sources: Batteries Photoelectric cells (used in calculators) Wall outlets Generators Nuclear power stations 2. Electrical Load An electrical load is anything that converts electrical energy into another form of energy. For example: Light bulb Can opener Oven Blender Toaster Television 3. Control Device A control device is used to control the circuit, whether it is on or off, open or closed. Switches Timers Thermostat Fuses Circuit Breakers 4. Connectors The connectors are the conducting wires that join the various parts of the circuit, for example: wires. Copyright Durham Continuing Education, 2005 Page 19 of 66

20 SNC1L Science Unit 3 Lesson 12 Insulators and Conductors Insulators An electric insulator is a substance in which electrons cannot move freely from atom to atom. If some atoms of an insulator become negatively charged with extra electrons, these electrons remain on the same atoms until removed by a substance that exerts a stronger force on the electrons. Typically insulators are the types of materials used to when needing static electricity. Insulators are types of materials, like plastic and rubber, that allow for the build up of static charges and because of this they can be very useful. Because electrons cannot be conducted through electrical insulators, these materials protect us from electric shocks. Two wire carrying electric current to an electric kettle would be very dangerous if they were not covered with a plastic or rubber insulating substance. Insulators cover many household tools and appliances. Electrical cords, plugs, wall sockets, and switches are actually metal conductors covered by an insulating substance. Conductors It doesn t matter how hard you rub a metal appliance or tap in the kitchen or bathroom because it will never build up static charge. Metals are electrical conductors. A conductor is a substance in which electrons can move freely from one atom to another. If a conductor becomes negatively charged with extra electrons, they move freely along the conductor. Table: Common Conductors and Insulators Good Conductors Fair Conductors Good Insulators Silver Carbon Oil Copper Nichrome Fur Gold Human Body Silk Aluminum Moist Human Skin Wool Magnesium Acid Solutions Rubber Tungsten Salt Water Glass, Plastic, Wood Do you recognize the list of good insulators from the electrostatic series in lesson 1? Copyright Durham Continuing Education, 2005 Page 20 of 66

21 SNC1L Science Unit 3 Lesson 12 This picture illustrates an electrical current traveling through a wire. The circle graphic shows what the wire would look like if you looked directly at its end. The image I'm holding is a wire that has been sliced down the middle so you can see the inside of it. The red spheres represent electrons. Support Question (These questions are NOT to be submitted for evaluation!) Complete the following sentences by filling in the blanks: (remember you cannot write in this book, therefore you must rewrite the sentences in you notebook) 13. Electric current is the or flow of from one place to another. 14. Electric circuits are used to electrical into the other forms of energy we need, such as and. 15. The 4 parts of an electric circuit are,,, and sources of electrical energy are and. 17. An example of an electrical load is. 18. An example of a control device is. 19. When a circuit is operating and the current is flowing, it is called a circuit. 20. An example of an insulator is and an example of a conductor is. Copyright Durham Continuing Education, 2005 Page 21 of 66

22 SNC1L Science Unit 3 Lesson 12 Types of Electric Current There are two types of electric current: direct current or DC and alternating current or AC. DC Direct Current Direct current is the type of electric current that flows continuously in one direction through a circuit. DC is produced from smaller energy sources like batteries. DC would be the type of current that would power your CD player, flashlight, calculator, or cell phone. Direct current is the direct flow of electrons, the current flows in one direction only and therefore cannot travel over great distances. AC Alternating Current The electricity that comes from the outlets in homes and provides the energy to operate appliances and light fixtures is called alternating current (AC). In AC, the flow of electrons reverses, first flowing in one direction, then flowing in the other. The electron flow reverses and therefore is able to travel over great distances without losing to much energy. Alternating current is the type of current that comes from a turbine, generator or nuclear power plant. Ways of Generating Electricity for Society Using Static Electricity Lightning Lightning is part of a natural process of exchanging electric charges between the atmosphere and Earth itself. Lightning is not artificially produced, therefore not technically created to power our homes or workplaces. However, lightning plays a very significant role in helping to sustain life on earth. Lightning is responsible for fixing the element nitrogen into the earth s soil and atmosphere. Without, Earth s vegetation would not be healthy and in abundance as it is today. Therefore, in a way, lightning helps in keeping us fed. Copyright Durham Continuing Education, 2005 Page 22 of 66

23 SNC1L Science Unit 3 Lesson 12 How does Lightning Occur? What do thunderclouds and static charge have in common? Inside a thundercloud, currents of air carry water droplets and ice particles upward. As the water droplets and ice particles travel inside the thundercloud, they rub against one another building up a static charge. The small, light positive particles rise to the top and the larger, heavier negative particles repel and move towards the bottom of the cloud. Because of the separation of opposite charges, static electricity exists and a spark or lightning flash appears between the top and bottom of the cloud. This type of lightning is called sheet lightning because it is hidden from view and is seen as a flickering of light within the cloud. Copyright Durham Continuing Education, 2005 Page 23 of 66

24 SNC1L Science Unit 3 Lesson 12 When the attraction between the negative charges at the bottom of the cloud and the positive charges on the ground become strong enough, a surge of electricity flows upward from the ground to neutralize the charge. This flow of energy is a lightning strike that spreads across the sky and is called fork lightning. Examples of Fork Lightning Using Current Electricity Fossil-Fuel Generating Stations Approximately 89% of the energy resources used in Canada are non-renewable. Nonrenewable energy sources are in the form of fossil fuels. Non-renewable energy resources are at a disadvantage because they cannot be replaced within our lifetime. It takes thousands of years to replace fossil fuels. The most common fossil fuels used in abundance by society are oil, natural gas and coal. In a generating station using any of the three forms of fossil fuel as the energy source, the fuel is burned, and the chemical energy released is used to heat water and produce steam. The steam is then used to turn turbines. As the turbines turn, they generate electricity that is transported to homes and businesses through electrical wires. Copyright Durham Continuing Education, 2005 Page 24 of 66

25 SNC1L Science Unit 3 Lesson 12 Nuclear Generating Stations Nuclear energy is used to generate electrical energy in several parts of Canada. The process is essentially the same as that used with fossil fuels. The basic difference is that, instead of using the chemical energy in the fuel to heat the water, the energy used is that released from nuclear reactions. Approximately half of Ontario s electrical energy production is supplied by nuclear generating stations. Advantages of Using Nuclear Power Nuclear power costs about the same as coal, so it's not expensive to make. Does not produce smoke or carbon dioxide, so it does not contribute to the greenhouse effect. Produces huge amounts of energy from small amounts of fuel. Produces small amounts of waste. Nuclear power is reliable. Disadvantages of Using Nuclear Power Although not much waste is produced, it is very, very dangerous. It must be sealed up and buried for many years to allow the radioactivity to die away. Nuclear power is reliable, but a lot of money has to be spent on safety - if it does go wrong, a nuclear accident can be a major disaster. People are increasingly concerned about this - in the 1990's nuclear power was the fastest-growing source of power in much of the world. Now, in 2005 it's the second slowestgrowing. Copyright Durham Continuing Education, 2005 Page 25 of 66

26 SNC1L Science Unit 3 Lesson 12 Solar Power We've used the Sun for drying clothes and food for thousands of years, but only recently have we been able to use it for generating power. The Sun is 150 million kilometers away, and amazingly powerful. Just the tiny fraction of the Sun's energy that hits the Earth (around a hundredth of a millionth of a percent) is enough to meet all our power needs many times over. In fact, every minute, enough energy arrives at the Earth to meet our demands for a whole year - if only we could harness it properly. There are three main ways that we use the sun s energy: Solar Cells - (really called "photovoltaic" or "photoelectric" cells) that convert light directly into electricity Solar Water Heating - where heat from the Sun is used to heat water in glass panels on your roof. Solar Furnaces - use a huge array of mirrors to concentrate the Sun's energy into a small space and produce very high temperatures. Hydroelectric Generating Stations Canada is fortunate to have many locations where it is possible to produce electrical energy by using the energy of falling water. Approximately 20% of Ontario s electricity was produced by hydroelectric generating stations, such as the one at Niagara Falls. The hydroelectric generating station in Niagara uses the falling water to turn the water turbine wheels at the bottom of the falls. The turbine wheels produce the electrical energy. Advantages of Hydroelectric Generating Stations Once the dam is built, the energy is virtually free. Copyright Durham Continuing Education, 2005 Page 26 of 66

27 SNC1L Science Unit 3 Lesson 12 No waste or pollution produced. Much more reliable than wind, solar or wave power. Water can be stored above the dam ready to cope with peaks in demand. Hydro-electric power stations can increase to full power very quickly, unlike other power stations. Electricity can be generated constantly. Disadvantages of Hydroelectric Generating Stations The stations are very expensive to build. However, many stations are also used for flood control or irrigation, so building costs can be shared. Building a large station will flood a very large area upstream, causing problems for animals that used to live there. Finding a suitable site can be difficult - the impact on residents and the environment may be unacceptable. Water quality and quantity downstream can be affected, which can have an impact on plant life. Constant Production of Electrical Energy One of the challenges of electrical energy is that it is difficult to actually store it once it has been produced. There is no practical way to store the huge amount of electrical energy produced at a generating station. Because electrical energy produced at a generating station cannot be stored, it must be used up at the same rate as it is generated. The rate at which energy is used is called electric power that is why generating stations are often referred to as power stations. The employees of generating stations are constantly adjusting the production of electrical energy to match the amount of energy being used by everyone all across Canada. Copyright Durham Continuing Education, 2005 Page 27 of 66

28 SNC1L Science Unit 3 Lesson 12 Key Questions #12 A) What are 2 important facts about static electricity? B) What are 2 important facts about current electricity? C) Give 2 example materials of an insulator. D) Give 2 example materials of a conductor. E) What does DC and AC stand for? F) Give an example of an electrical device in your home that would be powered by DC. G) Give an example of an electrical device in your home that would be powered by AC. H) How is lightning important to life on earth? I) List 3 ways of generating electricity for society. J) Pick one of the many ways of generating electricity for society mentioned during this lesson. Once you have decided on a type of generating station, using the internet, or your local library, answer the following questions: Could the type of energy be used where you live? Where would the generating station be located? How does the generating station produce electricity for society? These questions must be submitted for evaluation! Copyright Durham Continuing Education, 2005 Page 28 of 66

29 SNC1L Lesson 13 Electrical Circuits

30 SNC1L Science Unit 3 Lesson 13 Introduction In lesson 1, you learned about static electricity. In lesson 2, you learned about sources of electricity, how it is created and several different ways it is generated to benefit society. In lesson 3, you will learn how the electric circuit works. More specifically you will read about, electric potential, current, resistance and how they apply to series circuits. Have you ever thought why it is safer to touch some sources of electrical energy and very unsafe to touch others. For example you can hold a battery in your hand, even touch it to your tongue without being seriously hurt. However, everyone knows how dangerous it is to touch the terminals of a wall outlet. The difference between the battery and the wall outlet is in the amount of energy that each electron receives from the energy source before moving into the electric circuit. In this lesson we will discuss how to measure electricity and how to construct very simple circuits. What You Will Learn After completing this lesson you will be able to: Use scientific terminology during investigations to describe basic electrical concepts and related units of measurement (e.g., current ampere, potential difference volts, source, load, open and closed circuit, insulator, conductor) Demonstrate an understanding that electrical energy can be converted into other forms of usable energy within electrical circuits (e.g., heat, light, motion) Use a variety of symbols to represent different components in electrical circuits (e.g., ammeter, wire, switch, power source, load, voltmeter) Formulate scientific questions about circuits and create a simple plan to carry out investigation, including safety procedures Design, build and test an electrical circuit to investigate the chosen question, using appropriate safety procedures Extract and interpret information from instructions and manuals for circuits and electrical devices (e.g., explain a circuit diagram to a peer) Communicate plans and results of investigations about electrical circuits using a variety of oral, written and graphic formats Copyright Durham Continuing Education, 2005 Page 30 of 66

31 SNC1L Science Unit 3 Lesson 13 Current, Potential Difference and Resistance When electric charges move from one place to another, we say they make an electric current. Two terms used when working with electric current are potential difference or voltage and resistance or ohms. Term Definition Units of Measurement Electric Current Number of electrons moving past Amperes (A) a fixed point in a conductor in one second Voltage or Potential The force that moves electric Volts (V) Difference charges in a circuit Resistance The ability that tries to stop or slow the electric charges in a circuit Ohms (Ω) Current and Potential Difference Electric current is very similar to a flowing river. The river flows from one spot to another and the speed it moves is the speed of the current. With electricity, current is a measure of the amount of charge (or energy) transferred over a period of time. That stream of energy is a flow of electrons, or individual negative charges. Scientists use the value amperes when they measure current. One of the results of current is the heating of the conductor. more heat is created. When an electric stove heats up, it's because of the flow of current. The electrons have a mass (however small it may be), and when they move through the conductor there is friction. That friction creates heat. The more electrons bumping into the atoms of the conductor, the How do Electrons Move Through a Circuit? We need to know something about the force that causes the electrons to move in an electrical circuit. This force is called electromotive force, or EMF. Sometimes it is convenient to think of EMF as electrical pressure. In other words, it is the force that makes electrons move in a certain direction within a conductor. Copyright Durham Continuing Education, 2005 Page 31 of 66

32 SNC1L Science Unit 3 Lesson 13 But how do we create this electrical pressure to generate electron flow? There are many sources of EMF. Some of the more common ones are: batteries, generators, and photovoltaic cells. Batteries are constructed so there are too many electrons in one material and not enough in another material. The electrons want to balance the charge by moving from the end with the excess electrons (negative terminal, indicated by a sign) to the end with the shortage of electrons (positive terminal, indicated by a + sign). However, they cannot because there is no conductive path for them to travel. If these two unbalanced materials within the battery are connected together with a conductor, a copper wire for example, electrical current will flow as the electron moves from the negatively charged area to the positively charged area. When you use a battery, you are allowing electrons to flow from one end of the battery through a conductor and something like a light bulb to the other end of the battery. The battery will work until there is a balance of electrons at both ends of the battery. A word of caution: you should never connect a conductor to the two ends of a battery without making the electrons pass through something like a light bulb which slows the flow of currents. If the electrons are allowed to flow too fast the conductor will become very hot, and it and the battery may be damaged. To understand how voltage and amperage are related, it is sometimes useful to make an analogy with water. Look at the picture here of water flowing in a garden hose. Think of electricity flowing in a wire in the same way as the water flowing in the hose. The voltage causing the electrical current to flow in the wire can be considered the water pressure at the faucet, which causes the water to flow. If we were to increase the pressure at the hydrant, more water would flow in the hose. Similarly, if we increase electrical pressure or voltage, more electrons would flow in the wire. Does it also make sense that if we were to remove the Copyright Durham Continuing Education, 2005 Page 32 of 66

33 SNC1L Science Unit 3 Lesson 13 pressure from the hydrant by turning it off, the water would stop flowing? The same is true with an electrical circuit. If we remove the voltage source, or EMF, no current will flow in the wires. Key Concepts EMF is electromotive force. EMF causes the electrons to move in a particular direction. EMF is measured in units called volts. Resistance There is another important property that can be measured in electrical systems. This is resistance, which is measured in units called ohms. Resistance is a term that describes the forces that oppose the flow of electron current in a conductor. All materials naturally contain some resistance to the flow of electron current. We have not found a way to make conductors that do not have some resistance. If we use our water analogy to help picture resistance, think of a hose that is partially plugged with sand. The sand will slow the flow of water in the hose. We can say that the plugged hose has more resistance to water flow than does an unplugged hose. If we want to get more water out of the hose, we would need to turn up the water pressure at the hydrant. The same is true with electricity. Materials with low resistance let electricity flow easily. Materials with higher resistance require more voltage (EMF) to make the electricity flow. The scientific definition of one ohm is the amount of electrical resistance that exists in an electrical circuit when one amp of current is flowing with one volt being applied to the circuit. Is resistance good or bad? Resistance can be both good and bad. If we are trying to transmit electricity from one place to another through a conductor, resistance is not good in the conducting wire. Resistance causes some of the electrical energy to turn into heat so some electrical energy is lost along the way. However, it is resistance that allows us to use electricity for heat and light. The heat that is generated from electric heaters or the light that we get from light bulbs is due to resistance. In a light Copyright Durham Continuing Education, 2005 Page 33 of 66

34 SNC1L Science Unit 3 Lesson 13 bulb, the electricity flowing through the filament, or the tiny wires inside the bulb, cause them to glow white hot. An important point to mention here is that the resistance is higher in smaller wires. Therefore, if the voltage or EMF is high, too much current will follow through small wires and make them hot. In some cases hot enough to cause a fire or even explode. Therefore, it is sometimes useful to add components called resistors into an electrical circuit to slow the flow of electricity and protect of the components in the circuit. Resistance is also good because it gives us a way to shield ourselves from the harmful energy of electricity. We will talk more about this on the next page. Key Concepts Resistance is the opposition to electrical current. Resistance is measured in units called ohms. Resistance is sometimes desirable and sometimes undesirable. Support Question (These questions are NOT to be submitted for evaluation!) 21. Try this Investigation! Comparing Water Flow to the Flow of Electric Current The purpose of this activity is to compare water flow in a plumbing system to the flow of electric current in an electric circuit. In this investigation, you will need someone to help you! Materials Someone s help Two funnels of different sizes Cotton Water Two plastic containers After reading about potential difference, current and resistance attempt to answer the following investigation questions, while demonstrating your knowledge of electric current using the materials listed above. You must observe, record, and verbally communicate to your helper how a plumbing system is like electric current flowing in an electric circuit. The following diagram may help you set up the investigation. Have the helper hold the funnels under the stream of water from your kitchen sink. Copyright Durham Continuing Education, 2005 Page 34 of 66

35 SNC1L Science Unit 3 Lesson 13 Procedure 1. Explain how you would use the water flow to demonstrate a low voltage electric current. How would you demonstrate a high voltage electric current? 2. How would you change the funnel to represent an electrical wire that has a high current capacity, the ability to carry more electric current? How would you represent a low current capacity? 3. How could you use the funnel to represent an electrical line that has decreases resistance to the flow of electric current? How would you represent a line that has increased resistance to the flow of current? Copyright Durham Continuing Education, 2005 Page 35 of 66

36 SNC1L Science Unit 3 Lesson 13 Creating Electrical Circuits When we connect various components together with wires, we create an electric circuit. What we are creating is a path through which electrons can travel, creating electrical energy. The electrons must have a source of electrical energy that will create their movement and, of course, they need a path in which to travel. This path must be complete from the source through the other components and then back to the source. The voltage (or potential difference) for any electric circuit can come from many different sources. Some common examples are: batteries, power plants, fuel cells. When we plug an appliance into a wall outlet, voltage and current are available to us. That voltage is actually created in a power plant somewhere else and then delivered to your house by the power wires that are on poles or buried underground. As a matter of fact, since no current can flow unless there is a source or electrical energy or voltage source, we also refer to these sources as current sources. In other words, without the voltage source, there will be no current flowing. Batteries create voltage through a chemical process. Examine the following diagram: Battery (also referred to a cell) Picture of the inside of a battery Batteries or cells - are portable power sources. They contain a paste between two metal plates. The following cross section of a battery contains a carbon rod electrode and a conducting mixture of manganese dioxide. The metal ingredients of the middle section of the battery allows for a slow chemical reaction that results in the creation of electrical energy. Copyright Durham Continuing Education, 2005 Page 36 of 66

37 SNC1L Science Unit 3 Lesson 13 Power plants generate electricity from numerous mechanical methods. Some burn coal or gas to create steam while others use water flowing through a dam on a lake, refer back to the 2 nd lesson covered in this unit. There are also nuclear-powered generating power plants. All of these power-generating systems turn large turbines that turn the shaft on a generator. All of these sources of electricity convert something called potential energy to kinetic energy. The potential energy is stored in the fuel, whether it is coal, gas, uranium, water in a dam, etc. When we utilize these fuels to generate electricity, they become kinetic energy. We might say that potential energy is energy that is waiting to be used while kinetic energy is energy that is being used. In addition to the voltage source, we need to have wires and other components to build an electric circuit. Remember that copper wires are conductors since they can easily conduct the flow of electrons. We may also use resistors or other forms of loads to form a complete circuit. Note: If we did not include resistors in our circuit, there may be too much current flowing to and from our voltage source and we could damage the voltage source or start a fire. Examine the following examples of electrical circuits: Copyright Durham Continuing Education, 2005 Page 37 of 66

38 SNC1L Science Unit 3 Lesson 13 Circuit Diagrams Circuit diagrams are a pictorial way of showing circuits. Electricians and engineers draw circuit diagrams to help them design the actual circuits. Here is an example circuit diagram. The important thing to note on this diagram is what everything stands for. You see that there are straight lines that connect each of the symbols together. Those lines represent a wire. Symbol What the symbol represents in the circuit diagram This is the symbol for an Ammeter, an ammeter measures the amount of current. This is the symbol for a Voltmeter, the voltmeter measures the amount of potential difference across a load or source This is the symbol for a Resistor, a resistor slows the flow of electrons and changes electrical energy into another usable form This is the symbol for an open switch, if you wanted to indicate that the circuit was working or complete, the line would not be angled upwards, it would connect with the dot This is the symbol for 2 batteries or cells, in other words, a power source This is the symbol for the light bulb Rules for Drawing Circuit Diagrams When drawing circuit diagrams to represent a circuit that you have constructed you must do the following: 1. Use a ruler when indicating the connecting wires. 2. Use a pencil! 3. All corners of the diagrams must be drawn as perfect corners, making an angle of 90 - no rounded corners! 4. Use the symbols to represent the electrical devices that are a part of the circuit. Copyright Durham Continuing Education, 2005 Page 38 of 66

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