SCIENCE 9: PHYSICS UNIT I. STATIC ELECTRICITY B D A E SKILLS 1. Define static electricity and explain how static charges are built up

Transcription

1 NAME: SCIENCE 9: PHYSICS UNIT I. STATIC ELECTRICITY B D A E SKILLS 1. Define static electricity and explain how static charges are built up II. VOLTAGE B D A E III. CURRENT B D A E 2. Describe the rules of static electricity 3. Differentiate between Induction and conduction 4. Explain some applications and dangers of static electricity 5. Define voltage and identify the symbol 6. Producing voltage batteries and other sources 7. Define current electricity and identify its symbols BLOCK: 8. Distinguish between static and current electricity, and between electron flow and conventional current 9. Identify the necessary features of a complete circuit IV. RESISTANCE AND OHM S LAW B D A E 10. Define resistance and identify its symbols 11. Perform calculations using Ohm s law V. SERIES AND PARALLEL CIRCUITS B D A E 12. Identify the characteristics of a series and parallel circuit 13. Draw series and parallel circuit diagrams using appropriate symbols 14. Demonstrate the correct way of connecting voltmeters and ammeters % Physics Exam Result Beginning Developing Accomplished Exemplary Demonstrates a basic Demonstrates a solid understanding of concepts. understanding of concepts. Does not demonstrate a basic understanding of concepts. Demonstrates a complete and deep understanding of concepts. LEVEL Beginning Developing Accomplished Exemplary LETTER GRADE I/F C-/C C+/B-/B/B+ A-/A/A+ PERCENTAGE My estimate based on quizzes and assignments: % % of Unit Mark Assigned by my teacher: 70 My Physics Exam mark 30 1

2 To Do List This is a list of the activities in this unit. You can check off the activities as you complete them. ACTIVITY FINISH BY DATE Watch the Bill Nye video on static electricity and complete the worksheet while you are watching Using the text and the internet, complete the notes on static electricity Complete the Static Electricity Worksheet With a partner, complete the Static Electricity Lab and the accompanying questions Complete quiz on Static Electricity Use the text, our website and the internet to complete II. Voltage Notes. Make your Foldables Study Summary package as per BC Science 9 p Use the topics suggested in your package, or use your own. Fill it in as you go on. Complete quiz on Voltage Use the text, our website, and the internet to complete III. Current Notes. Complete the two worksheets: Circuit Diagrams & What s wrong with these circuits? Fill in your foldable Compete the Squishy Circuits lab and the accompanying questions Complete quiz on Current Use your text, our website, and the internet to complete IV. Resistance and Ohm s Law Notes. Complete the Ohm s Law activity tion. Complete the worksheet: Ohm s Law. The final answers are given after each ques Fill in your foldable Complete quiz on Resistance and Ohm s Law Use your text, our website, and the internet to complete V. Series and Parallel Circuits. Part (1) Series Circuits Notes Complete the worksheet: Series Circuits Fill in your foldable Use your text, our website, and the internet to complete the notes on V. Series and Parallel Circuits. Part (2) Parallel Circuits Complete the worksheet: Parallel Circuits Complete the worksheet: Parallel and Series circuits Complete the online simulation: resistors in series and parallel circuits Compete the Squishy Circuits lab and the accompanying questions Complete the series and parallel circuits comparison table Fill in your foldable Complete quiz on Series and Parallel Study for Last Unit Exam: Finish foldable Some review is included in your Physics package. Much more available on-line! 2

3 INTRO: BILL NYE VIDEO STATIC ELECTRICITY Complete while the video is playing! 1. Charged particles that build up and don t flow: electricity. 2. Static electricity is from a word that means. 3. Electrons build up a big charge and then the charge lets go. The electrons start flowing. Isn t that wild; it s. 4. A static charge occurs when electrons on something. 5. What do opposite electric charged do when they are brought close to each other? 6. Why do the hairs of Bill Ney s Rocking Wig of Science stand out as they do? 7. Clothes taken out of the dryer often stick together. This is called: 8. Static on radios and tvs is picked up by antennae and is caused by static on and in the atmosphere. 9. When electrons jump off of things, scientists say that they 10. Bills Generator has a ground wire that runs from the machine right to the main cold 11. The pipes run underneath the floor to the lab, all the way down into the 12. You may have seen the third prong on some electrical plugs; it s the. It lets extra electrons get to or from the quickly and quietly. 13. Lightning can strike backwards from the to a. 14. In Bill Nye s story time, he mentions that long ago pine tree sap hardened into a gold coloured substance we call 15. What is the Greek word for amber? 16. The top of the Space Needle in Seattle, Washington, is about 184 m off the ground, very close to the clouds. As a result, there is a on it. If an electrical storm comes along, the electrons can find their way to the through one of these things. 17. The safest place to be in a thunderstorm is in your 18. Static electricity isn t always static. That is it doesn t always 3

4 Using the BC Science 9 text (starting p.248) and/or the internet, complete the following set of notes I. STATIC ELECTRICITY NOTES There are two types of electricity: and Static electricity is: e- can be transferred from one object to another via static electricity can t be forced through a wire or circuit (that s called electricity) most objects are neutral meaning the # of = the # of diagram; Atomic Structure Friction & Electron Transfer What is friction? Solids become charged by gaining or losing When two objects are rubbed together, one can lose to the other. For example: Rubber has a much greater attraction for electrons than animal fur. as a result, the atoms of rubber pull from the atoms of animal fur this leaves both objects with an imbalance of charge: o The rubber balloon has an of electrons so it has a charge o the animal fur has a of electrons which leaves it charged. different materials have different for electrons. What is the triboelectric series? (look it up!) Example: Acetate (plastic) + paper towel e paper plastic On separate paper, do the Reading Check Questions on p

5 INSULATORS & CONDUCTORS (text starting on p. 252) Insulator: Conductor: Examples: Examples: LAWS OF STATIC CHARGE What is a force? Rules for Static Charge CHARGING BY INDUCTION OR CONDUCTION Important! Remember that objects become: negatively charged by and positively charged by protons never leave the Induced Charge: Conduction: Compare induction vs. conduction 5

6 USES AND DANGERS OF STATIC ELECTRICITY Van de Graaf Generator Draw a diagram and describe how it works: Lightning Describe the process that produces lightning: What is an electrical discharge? Safety Tips for Electrical Storms QUIZ QUESTIONS: Things I think might be on the next quiz: 6

7 STATIC ELECTRICITY WORKSHEET Acetate Atoms conductors coulomb Electric Electrons grounding insulators Vocabulary Negative Neutral Neutrons nucleus Positive protons static charge Van de Graaff generator Use the terms in the vocabulary box to fill in the blanks. You may use terms more than once. You will not need to use every term. 1. Static electricity is also known as. This refers to the build-up of electric charge in one place. 2. All matter is made of tiny particles called. 3. The positively charged is the center of the atom. It consists of positively charged subatomic particles called and subatomic particles with no charge called. 4. The negatively charged subatomic particles called occupy the area around the nucleus. 5. An object is uncharged or when the number of positive charges equals the number of negative charges. 6. If an atom loses an electron, it has more protons than electrons. This atom will have an overall charge. 7. If an atom gains an electron, it has more electrons than protons. This atom will have an overall charge. 8. Glass and acetate are examples of because they do not allow electrons to move easily through them. Metals like copper and aluminum are good because they allow electrons to move freely through them. 9. The is a unit of electric charge. 10. Scientists use a(n) to create static charge. 11. Lightning rods on top of buildings allow static charges from lightning to flow into the Earth s surface. This is known as. 7

8 Use the following diagram to answer the questions that follow. Tendency to to Lose electrons Tendency electrons + - gain Glass human hair wool cat s fur silk cotton paper balloon vinyl plastic rubber When 2 objects are rubbed together: The material closer to the left of the series will have have a greater tendency to lose electrons and become positive the material closer to the right of the series will a greater tendency to gain electrons and become negative 12. As you take your clothes out of the dryer, your wool socks are clinging to your silk shirt. What is the charge on the wool sock and on the silk shirt? Charge on the socks: Charge on the shirt: 13. You use a plastic comb to comb your hair. What is the charge on your hair and on the comb? Charge on the hair: Charge on the comb: 14. You use a paper towel to rub off some dirt on a glass window. What is the charge on the glass and on the paper towel? Charge on the glass: Charge on the paper towel: 15. You rub a balloon along your cat s back, causing the cat s fur to stand up. What is the charge on the balloon and on the cat s fur? Charge on the balloon: Charge on the cat s fur: 16. Using the list of words below, complete the following sentences. Each word may be used more than once. opposite, positive, positively, neutral, negative, negatively A. charges are unlike charges. B. Two like charges are either both or both. C. If two charges are brought together, they will be attracted to one another. D. If a charged object is brought near a positively charged object, they will repel. E. If a charged balloon is brought near a positively charged object, the balloon is attracted to the positively charged object. 8

9 Use the following diagram to answer questions Use (-) to represent negative charges and (+) to represent positive charges The diagram above represents a neutral solid object. What is the relationship between the number of positive and negative charges in a neutral object? 18. When the above neutral object is rubbed with a material, it becomes positively charged. (a) Draw a new diagram that represents the object with a positive charge. (b) How do the number of positive charges compare to the original diagram? (c) How do the number of negative charges compare to the original diagram? 19. When the neutral object is rubbed with a different material, it becomes negatively charged. (a) Draw a new diagram that represents the object with a positive charge. (b) How do the number of positive charges compare to the original diagram? (c) How do the number of negative charges compare to the original diagram? 20. Use the words increased (I) or decreased (D) to complete each of the following statements. (a) To increase the electric force between two charged objects, the distance separating the charges should be (b) To increase the electric force between two charged objects, the amount of charge on one or both objects should be (c) To decrease the electric force between two charged objects, the distance separating the charges should be (d) To decrease the electric force between two charged objects, the amount of charge on one or both objects should be 21. The diagrams below show two charged balloons hanging on thin threads. One balloon in each diagram is identified as either positive (+) or negative (-). The arrows indicate whether the two balloons are attracted or repelled. On the diagrams, label the charges on the unidentified balloons. (a) (b) (c) 9

10 Static Electricity Lab You will see stations set up around the perimeter of the classroom. Stations may be completed IN ANY ORDER. Here are directions and questions at each station. Spread yourselves out! Use the table provided below to record your answers and observations. STATION 1 1. Sticky Wall STATION 2 1. Dancing Cereal STATION 3 1. Opposites Attract STATION 4 1. Salt and Pepper STATION 5 1. Snake Charmer STATION 6 1. Rolling Can STATION 7 1. Magic Wand 10

11 II. VOLTAGE NOTES Borrow a BC Science 9 text to complete the notes Electric Potential Energy and Voltage Energy = the ability to Electric energy that is stored is energy Electric energy that is moving is energy. Electrons separated from the positive nucleus want to return to their original location If the electrons are held separated, then these electrons have energy. The amount of energy the separated electrons possess is dependent upon (1) (2) Electrochemical cells convert energy into energy. chemical energy separates the from the charges Battery Connecting together forms. It is now accepted language to refer to all electrochemical cells as batteries, regardless of the number of cells involved. The ends of batteries, where we make a connection, are called. Extra e- accumulate on one terminal making it charged e- left from the other terminal, leaving that terminal charged when the battery is connected to an electrical device, can flow through the. The energy is transformed into other forms of energy (eg. Sound, heat, light ) Batteries change E into E 11

12 Electric Potential Difference/Voltage Potential difference, or voltage as it is more commonly called, is proportional to the that the charges have been separated. The actual potential energy is the product of both the and the amount of (Energy =Voltage Charge). The unit of electric charge is the whose symbol is: One coulomb = e- (gained or lost) The amount of electric potential energy per coulomb of charge is called the or. The unit of voltage = whose symbol is: measures the amount of potential difference between two locations Voltage is sometimes thought of as a force motivating electrons to " " in a circuit specific measure of potential energy that is always relative between. When we speak of a certain amount of voltage being present in a circuit, we are referring to the measurement of how much potential energy exists to move electrons from one particular point in that circuit to another particular point. Without reference to two particular points, the term "voltage" has no meaning. Producing Voltage Batteries come in 2 basic types: 1. : batteries in flashlights, watches, etc. 2. : car batteries Two terminals on a battery are called Usually made of 2 different or a metal + Electrodes are in an Electrolyte: The electrolyte in a dry cell is a. The electrolyte in a wet cell is a 12

13 Electrochemical Cell: Amount of voltage produced depends on the types of, and the used. Batteries change chemical E E by charge Other forms of energy can also be used to separate charge and provide electrical E Connecting a Voltmeters Measures how much energy the e- lost while falling through the load (voltage drop), or gained while raised through the battery. Voltmeters are connected around the load or the battery Measuring the voltage drop across the light bulb Measuring the voltage of the battery Reading a Voltmeters Watch the online video on how to read a voltmeter (available at msveenstra.weebly.com under physics materials) PRACTISE Voltage = 7.2 V Voltage = Voltage = Voltage = 13

14 STUDY SKILL: Foldables Get a BC Science 9 textbook and open to page 269. You are going to produce a similar foldable for yourself. You need to choose your topics. Here are some suggested headings: 1. Producing Static Charge and Induction versus Conduction 2. Relationships between Charged Objects (Rules) 3. Uses and Dangers of Static Electricity 4. Voltage 5. Current 6. Resistance 7. Ohm s Law 8. Series Circuits 9. Parallel Circuits Your foldable should contain useful key ideas, diagrams and tables. Make this your go-to study guide! What is on the next Quiz?!! Before continuing, look back at what you have learned about current electricity so far, and check out the required skills for this section. Now decide what questions YOU think will be on the next quiz. Write down 10 questions, with answers. Find two buddies to share with. Did they have ideas you didn t think of? Did you? Between the three of you, have you pretty much got the questions for the next quiz? Now all you need to do is practice! 14

15 III. ELECTRIC CURRENT NOTES Borrow a text (or use the on-line version) to complete the notes Current electricity is defined as the amount of passing a point in a conductor every unit for measuring current is the whose symbol is: and is defined as: device used to measure current is the Electric circuit is any pathway that allows electrons to leave a source and eventually return to that source Electric circuit must contain at least one source of In electric circuit electrons flow through devices called in the circuit that convert electricity to Loads are things like: What is Conventional Current? And how is it different from electron flow? SIMPLE CIRCUITS The path of electrons E in the battery gives e- on the terminal of the battery energy. e- are attracted to the terminal the is the pathway they e- can travel through e- leave the terminal and are pushed by the E of the (voltage) E is converted into energy in the light bulb (load) complete the circuit by travelling the rest of the way back to the terminal of the battery How is current electricity and static electricity different? IMPORTANT NOTE: Upon returning to the source, all of the Electric potential energy in the charge must be converted to other forms of energy 15

16 Basic Circuit Components and Diagrams Give a description (in your own words) for the four basic components: 1. Source: 2. Conductor: 3. Electric Load: 4. Switch: Describe how a flashlight works: Basic Circuit Diagrams All circuit diagrams should be drawn using a ruler. All turns in the circuit should be drawn at 90 angles. Not all circuit diagrams will be identical The size & spacing of the components is not important, but the components should be in the same order as the initial illustration. The battery in a circuit may be symbolized as either a battery or a cell. Modern convention is to use the cell symbol to represent both cells and batteries Connecting Ammeters in a Circuit An ammeter counts the number of coulombs passing a particular point every second In order to connect an ammeter to a circuit, you must break the circuit and insert the meter. Ammeters becomes part of the pathway 16

17 CIRCUIT DIAGRAM WORKSHEET: Drawing labelled circuit diagrams. Draw the circuit diagrams described below. Be sure to use the proper circuit symbols, and label your drawings. Description 1. Draw a circuit diagram consisting of a 9.0 V battery, an ammeter, and a 25 resistor. Include a voltmeter that is measuring the potential difference across the resistor. 1. Diagram Show the direction in which the electrons flow Show the direction in which the electrons flow. 3. Draw a circuit diagram consisting of a battery made up of four 1.5 V cells, one closed switch, one lamp, one resistors, and a voltmeter measuring the potential difference across the light. 3. Show the direction of the conventional current flow. 17

18 What's Wrong With These Circuits? 1. Explain why the light bulbs won't light in the circuit pictured on the right. 2. Explain why the light bulb isn't lighting up in the circuit pictured on the right. 3. Explain why the light bulb isn't lighting up in the circuit pictured on the right. Super Teacher Worksheets - m 18

19 SQUISHY CIRCUITS LAB ACTIVITY Supplies provided for each group of students: 4-AA Battery pack with leads Conductive dough Insulating dough Buzzers Motor LEDs Safety In general, Squishy Circuits is a very safe activity. However, some safety notes should be addressed: LEDs should not be hooked directly to the battery packs. They will burn out and may pop. LEDs require a resistor to limit the amount of power flowing through them. With Squishy Circuits, the conductive dough acts as the wire and a resistor, so they re safe to use with the dough. Let s investigate a simple circuit using Squishy Circuits! 1. Take two pieces of conductive dough (coloured) and put each battery terminal into one of the pieces. 2. Find an LED and separate the terminals apart. Notice: one is longer than the other. 3. Create a circuit by placing each terminal of the LED in the conductive dough pieces. The longer LED terminal should go in the dough with the RED battery lead. 19

20 4. Try making a short circuit by pushing the two dough pieces together 5. Pull the dough apart again and insert a piece of insulating dough between them. 6. Get creative! Try your buzzers and motor! FOLLOW-UP QUESTIONS: 1. In step 3, what happens to the LED light? Why do you think that happened? 2. In step 4, what happens to the LED light? Why do you think that happened? What is a short circuit? 3. What happened when, in step 5, you inserted a piece of insulating dough between the two conducting pieces? Why do you think that happened? 4. What is electricity? 5. What is a conductor? 6. What is an insulator? 7. How can you tell that energy is moving (transferred) from the battery pack and through the dough? 8. When is there energy present in the circuit? a. How could you prove this? 9. What components (parts) are needed to make a circuit work? 10. What configurations of insulating and conductive dough work to construct a functioning circuit? 20

21 IV. RESISTANCE AND OHM S LAW NOTES Using the BC Science 9 text and/or the internet, complete the following set of notes Resistance is: e- tend to move through conductors with some degree of, or opposition to motion. the amount of current in a circuit depends on the amount of voltage available to motivate the electrons, and also the amount of resistance in the circuit to oppose electron flow. Just like, resistance is a quantity relative between two. For this reason, the quantities of voltage and resistance are often stated as being "between" or "across" two points in a circuit. Ohm s Law shows how,, and, relate mathematically Quantity Symbol Unit Unit Abbrev. Meter used for measurement Current Voltage Resistance Formula for OHM S LAW: V = IR In this algebraic expression, voltage (V) is equal to current (I) multiplied by resistance (R). Using algebra techniques, we can manipulate this equation into two variations, solving for I and for R, respectively: Formula for calculating: I = R = V = 21

22 Example: What is the amount of current in the circuit above? Solution: I = V = 12 V = 4A R 3Ω Practice: What is the amount of resistance (R) offered by the lamp in the diagram above? Solution: R = V = 36 V = 9 Ω I 4 A Practice: What is the amount of voltage (V) offered by the source in the diagram above? Solution: V = IR V = (1.5 A) ( 10 Ω + 5 Ω) = 22.5 V 22

23 OHM S LAW ACTIVITY Materials: Light, battery, ammeter and voltmeter Instructions Labelled circuit diagrams 1. Set up a circuit with one battery and one light bulb. Correctly connect the ammeter and the voltmeter. Measure the voltage and current of the bulb (record the data in the table) be sure to pay attention to the light's intensity. 1. Set up a circuit with two batteries and one light bulb. Correctly connect the ammeter and the voltmeter. Measure the voltage and current of the bulb (record the data in the table) be sure to pay attention to the light's intensity. Intensity of light Measured voltage Measured current Calculated resistance 23

24 OHM LAW WORKSHEET Answer the following questions onto separate paper. Show ALL your work. Final answers are given in square brackets following the question. 1. What is the resistance of a toaster if a current of 12.5 A flows through it when it is connected to 120 V? [9.6 Ω] 2. A light bulb has a resistance of 90 Ω. What current flows through the bulb when it is connected to 120 V? [1.3 A] 3. A current of 0.50 A flows through a light bulb that has a resistance of 18 Ω. What is the voltage across this light bulb? [9.0 V] 4. A flashlight bulb has a resistance of 4.0 Ω. What current passes through the bulb if it is connected to 3.0 V? [0.75 A] 5. What voltage is necessary to produce a current of 0.60 A in a load that has a resistance of 25 Ω? [15 V] 6. The current through a load in a circuit is 2.5 A. If the potential difference across the load is 75 V, what is the resistance of the load? [30 Ω] 7. (a) An 80 V potential difference is measured across a light bulb that has a resistance of 16 Ω. What is the current through this light bulb? [5.0 A] (b) If the light bulb was replaced by a bulb with twice the resistance, what would be the new current through the bulb? [2.5 A] 8. A 25 ma current flows through a 300 Ω lamp. What is the voltage across the lamp? [7.5 V] 9. What is the current flowing through a 5 ohm resistance when it is cone ted to a source of 10 volts? [2 A] 10. What is the size of the resistance that allows a current of 2.5 amperes to flow through when it is connected to a source of 100 volts? [40 Ω] 11. What is the voltage that will push eight amperes of current through a resistance of twenty ohms? [160 V] 12. What is the current flow, in amperes, when a five ohm resistance is connected to a source of one hundred volts? [20 A] 13. Calculate the resistance that allows a current of 134 milliamperes to flow when it is connected to a source of 220 volts. [1642 Ω] 14. What is the voltage that will push a current of.068 amperes through a resistance of 47 kilo-ohms? [3196 V] 15. If a 1.2 ohm resistance is connected to a source of 25 volts, what will the current flow be? [20.8 A] 16. A 220 ohm resistance is connected to a voltage source. The measured current flow is 2.3 milliamperes. What is the voltage? [.506 V] 17. A 12 volt car battery is connected to a resistance of 0.8 ohms. What is the current flow? [15 A] 18. A truck battery of 12 volts is used to start a truck engine. The current drawn was 400 amperes. What was the resistance of the starting motor? [0.03 Ω] 19. A certain lamp is connected to a source of 115 volts. The current was measured to be 0.7 amperes. What was the resistance of the lamp? [164 Ω] 20. A lightbulb requires a current of 0.50 A to operate at full brightness, and its filament has 240 Ω of resistance. How much voltage needs to be applied to this light bulb? [120 V] 24

25 V. SERIES and PARALLEL CIRCUITS NOTES Using the BC Science 9 text and/or the internet, complete the following set of notes PART 1. SERIES CIRCUITS NOTES Only one for the e- to flow. Any e- in a series circuit must travel through of that pathway Current measured anywhere in the series circuit will be because there are no alternative routes for the e- to travel The sum of the lost on the loads equals the total voltage supplied by the battery When e- leave the terminal of the battery they have a given amount of When these e- return to the, they must have all their electrical energy Each uses a portion of the supplied by the source Adding means that each e- must now pass through that and therefore the total of the circuit ADDITIONAL NOTES: 25

26 SERIES CIRCUIT BASIC RULES Read the online document about series circuit and their basic rules: 1. The current flows through each part of a series circuit. Make a drawing illustrating this rule: 2. The total resistance of a series circuit is equal to of individual resistances RT = 3. Voltage applied to a series circuit is equal to the of the individual voltage drops. Example: Calculate the voltage drop across each resistor: The battery is supplying 9 volts to the circuit of three resistors. The resistors have values of 50 Ω, 300 Ω and 100 Ω According to the previous rules we figure out the total resistance: RT = Next we calculate the amperage in the circuit: I = V/RT = We can calculate what the voltage drops across each resistor is using Ohm's Law: V1 = IxR V2 = V3 = VT = 4. The voltage drop across a resistor in a series circuit is directly proportional to the the resistor. 5. If the circuit is broken at any point. Example: 26

27 WORKSHEET: SERIES CIRCUITS Circle the best term in the parentheses to correctly complete each statement. 1. A series circuit has (more than one, only one) path for current to travel. 2. In a series circuit, the current at one location in the circuit is (equal to, different from) the current at another location in the circuit. 3. If two different resistors are connected in series, the voltage across one resistor will be (equal to, different from) the voltage across the second resistor. 4. By adding a resistor in series with an original resistor, the total resistance of the circuit (increases, decreases). 5. The sum of the voltages across each of the resistors in a series circuit is (equal to, different from) the voltage supplied by the battery. Find the unknown voltage at V, and current at A, in each of the following circuits. 6. Voltage = Current = 7. Voltage = Current = 8. (a) What is the total resistance in the circuit? (b) What is the amount of current flowing through Resistor 2? (c) Using Ohm s Law, determine the voltage drop across Resistor (a) What is the total voltage in the circuit? (b) What is the amount of current flowing through Resistor 2? (c) Use Ohm s law to determine the resistance of Resistor 3. 27

28 V. SERIES and PARALLEL CIRCUITS NOTES PART 2. PARALLEL CIRCUITS NOTES Using the BC Science 9 text and/or the internet, complete the following set of notes A parallel circuit is one that has or more paths for the electricity to flow, the loads are to each other. It's like a river that has been divided up into smaller streams, however, all the streams come back to the point to form the river once again. If the loads in the circuit were light bulbs and one blew out, there is still flowing to the others because they are still in a direct path from the negative to positive terminals of the battery. The parallel circuit has very different characteristics than a series circuit. The total resistance of a Parallel Circuit is NOT equal to the sum of the resistors (like in a series circuit). The total resistance in a parallel circuit is always less than any of the branch resistances. Adding more parallel resistances to the paths causes the total resistance in the circuit to decrease. As you add more and more branches to the circuit the total current will increase because Ohm's Law states that the lower the resistance, the higher the current. PARALLEL CIRCUIT BASIC RULES Read the online document about parallel circuit and their basic rules: 1. A parallel circuit has two or more for to flow through. 2. is the same across each component of the parallel circuit. Make a drawing illustrating this rule: 3. The sum of the through each path is equal to the total current that flows from the. IT = 4. You can find total resistance in a Parallel circuit with the following formula: 1/RT = 5. If one of the parallel paths is broken, current will to flow in all the other paths. 28

29 WORKSHEET: PARALLEL CIRCUITS Circle the best term in the parentheses to correctly complete each statement. 1. A parallel circuit has (only one, more than one) path for current to travel. 2. Two different resistors are connected in parallel. The current through one of the resistors will be (equal to, different from) the current through the other resistor. 3. If two different resistors are connected in parallel, the voltage across one resistor will be (equal to, different from) the voltage across the second resistor. 4. By adding a resistor in parallel with an original resistor, the total resistance of the circuit (increases, decreases). 5. The total current entering the junction of a parallel circuit must be (equal to, different from) the sum of the currents through each branch of the parallel circuit. Find the unknown voltage at V, and current at A, in each of the following circuits. 6. Voltage = Current = 7. Voltage = Current = 29

30 WORKSHEET: SERIES AND PARALLEL CIRCUITS Draw a diagram of each of the following circuits in the spaces provided. Description Diagram 8. A series circuit consisting of: 12 V electrical source open switch two light bulbs 10 resistor 9. A parallel circuit consisting of: 9.0 V electrical source open switch three 5.0 resistors 10. A circuit consisting of: three 1.5 V cells connected in parallel open switch two light bulbs connected in series two 15 resistors connected in parallel 11. Describe what will happen in the circuit shown above if (a) the switch is closed (b) the switch is closed and the first bulb is removed (c) the switch is closed and the fifth bulb is removed 30

31 12. Calculate the missing quantities for the circuit below. 13. Calculate the missing quantities for the circuit below. 14. Series Circuit Parallel Circuit The bulbs are (brighter, dimmer) (more, less) voltage across each bulb (more,less) current passes through each bulb The bulbs are (brighter, dimmer) (more, less) voltage across each bulb (more,less) current passes through each bulb 31

32 COMPARING SERIES AND PARALLEL CIRCUITS SERIES PARALLEL NUMBER OF PATHWAYs FOR THE ELECTRONS SIMPLE CIRCUIT DIAGRAM (one source, three bulbs) BATTERY LIFE CURRENT THROUGH CIRCUIT VOLTAGE THROUGH CIRCUIT EFFECT OF BREAKS IN THE CIRCUIT JUNCTION POINTS/NODES FAVORITE ANALOGY 32

33 ONLINE SIMULATION: RESISTORS IN SERIES AND PARALLEL CIRCUITS (Using CCK simulation) I. Series Circuit Construct the circuit figure 1 using The Circuit Construction Kit (CCK) simulation at the PHeT site. Make the resistors have different value and record the value of each resistor. Use the ammeter moving it to take readings in the different places seen in figure 2. Then use the voltmeter to take voltage readings. Calculate R using Ohm s Law (V=IR) for the total resistance in last column. Figure 1 V Figure 2 A A 1 A A V V V Resistor Voltage (V) Current (A) Resistance ( ) Total VT reading AT reading RT=VT/IT a. What is the relationship between the total resistance and the individual resistances? b. What is the relationship between the total current and the individual currents? c. What is the relationship between the total voltage and the individual voltages? b. Write a small paragraph explaining what you think is happening in series circuits to cause the above relationships to occur. 33

34 II. Parallel Circuits Wire the circuit in figure 1 with the same value resistors that you used in Part 1. Take readings in different places shown in figure 2 by moving the meters. Calculating total resistance using Ohm s Law (V=IR) for the last column. VT A R V A A2 Figure 1 Figure 2 R R V A A3 A V Resistor Voltage (V) Current (A) Resistance ( ) Total VT reading AT reading RT=VT/IT a. What is the relationship between the total resistance and the individual resistances? b. Look up the mathematical relationship for finding total resistance in a parallel circuit. Show that your data fits the equation. c. What is the relationship between the total current and the individual currents? d. What is the relationship between the total voltage and the individual voltages? e. Summarize the similarities and differences between the series and parallel circuits. Include your reasoning about what you think is happening. 34

35 SQUISHY CIRCUITS LAB ACTIVITY #2 Last time, we went through the basics of how to make simple electrical circuits with play dough and light-emitting diodes, now it's time to experiment with series and parallel circuits. Remember that diodes only conduct electricity in one direction, so if yours aren't lighting up, take them out and flip them around. CLOSED AND OPEN CIRCUITS For a current to flow, each element in an electric circuit must be electrically connected to the next to form an unbroken 'loop' from one of the battery's terminals all the way back to the other. When all the elements are properly connected, the circuit is 'closed' and a current can flow. Set up a simple closed circuit consisting of a battery pack, one LED and two blobs of conducting dough Did it light up? Why or why not? Set up a simple open circuit consisting of a battery pack, one LED and three blobs of conducting dough Did it light up? Why or why not? Use a 1 cent coin to acting as a switch to 'close' the circuit you just made. Did the LED light up? Try using other objects to 'close' this circuit. Only objects that conduct electricity will work, so this simple circuit doubles as a very basic "conductivity tester". Draw what you made: Draw a simple circuit diagram: 35

36 CONDUCTORS AND INSULATORS Try this: Try this: Draw a picture of simple closed circuit consisting of a battery pack, one LED and two blobs of insulating dough Ordinary play dough conducts electricity quite well but it is not a perfect conductor. Perfect conductors, known as 'superconductors' have zero electrical resistance. Play dough, on the other hand, does have some electrical resistance. In this picture, the electric current is taking the shortest path through the LED In this picture, the current is taking the long route to the LED and is passing all the way through the two long play dough 'wires'. Is there a difference in how the LED looks this time? Did it light up? Why or why not? How did the light from the LED s in the first two circuit compare? SERIES CIRCUITS Using your conductive dough, make a circuit that works like the schematic diagram to the right. Draw a picture of your dough circuit in the empty space. Add an LED to make the circuit diagramed here. Draw your dough circuit. What do you notice about the lights? What happens if you remove one of the lights? Why? 36

37 Add another LED to make the circuit diagramed here. Draw your dough circuit. What do you notice about the lights now? PARALLEL CIRCUITS What do you notice about the LEDs? What happens if you remove one LED? Why does this happen? Using your conductive dough, make a circuit that works like the schematic diagram to the right. Draw a picture of your dough circuit in the empty space. What do you notice about the LEDs? What happens if you remove one LED? Why does this happen? Try adding five LEDs in parallel. Draw a schematic: Draw your dough circuit: CHALLENGE: (1) Create a configuration that act as a switch to turn a buzzer off and on. (2) Create a circuit that has three lights than can be turned off and on independently and has a buzzer that can also be turned on or off independently of the lights 37

38 ELECTRICITY REVIEW 1. Complete this concept map about the characteristics of electricity. 38

39 2. List the similarities and differences between series and parallel circuits Series Parallel 39