Name: _____________________ Unit 9:1 Electricity and Why it Moves Period: _____________________ Electricity Electricity is moving electrons; Protons can’t move. Electrons can move, but protons are held together in the nucleus by the strong nuclear force, the strongest force in nature. – – + + – – Objects can be positive, negative, or neutral. The unit of charge is the coulomb (C). Charge Negative Electrons + – + – – +– + Positive Protons – A neutral object has an equal amount of protons and electrons. Electricity comes from electrons moving between atoms. + – – –+ –+ – – – + + – – + + + A positive object has lost electrons, so it has more protons than electrons. Any two charges feel a force between them. Electric force depends on the types of charges, the distance between the charges, and the amounts of the two charges. Electric Force Attracting Force – + + Positive hydrogen atoms in water are attracted to the negatively charged balloon, causing the water stream to bend slightly toward the balloon. Separating Charges Less force Repelling Force Opposites attract Just like gravity, electric force increases as distance decreases. Closer charges: more force. + Likes repel + + More force + + ++ ++ Naturally, objects are neutral. Work must be done to separate charges. Separating charges cause a charge difference and the electric force tries to move the charges back to neutral. If there is a difference of charge electricity can move between objects. A big enough difference can cause electricity to arc (jump a gap). Bigger differences of charge allow bigger arcs. No difference in charge—electricity can not move. arcing rubber rod – – – neutral – – – – – – – – – – – Afterwards the rod is charged and it can exert an electric force. To ground something you can often touch it to a pipe. Metal pipes are good electrical conductors and usually connected to ground somewhere in the building. + Electric force increases if either of the charges increases. More charge: more force. More force Two charged balloons repel each other, so they must be the same charge (negative). fur or hair Ground + Less force When two insulators rub, charges move between them, causing a separation of charge (static electricity) and an electric force. cstephenmurray.com A negative object has gained electrons, so it has more electrons than protons. – A Van de Graaff generator produces a charge difference. A big charge difference can push thru big gaps, like lightening arcing all the way to the ground. Batteries – + Batteries cause electrons to move by separating charges in chemicals. When connected by wires the charge can flow, eventually neutralizing the battery. . Ground (the earth) can take or give an infinite number of electrons. Ground is electrically neutral. Both positive and negative charges will neutralize when grounded. – + + – + + e’s – – – – – A positive object will take electrons from ground. Symbol for ground Legal copying of this worksheet requires written permission. – –+ –+ – – – + + – – e’s – – – – – A negative object will give electrons to ground. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9:1 Period: _____________________ 1. Positive 2. Negative 3. Neutral A. A push or pull caused by charges. 1. Ground A. The symbol for ground. B. The units for charge. 2. Arcing B. Moving electrons. 3. Charge Difference C. When a spark jumps between two objects. 4. Van de Graff D. Can accept or give an infinite amount of electrons. Will neutralize charge. C. When an object has more protons than electrons. 4. Coulombs D. When an object has an equal number of electrons and protons. 5. Electric force E. What keeps protons bound in the nucleus of an atom. 5. Electricity E. A machine that separates charge. 6. Strong Nuclear Force F. 6. F. When an object has more electrons than protons. Attract or Repel? ___ Two positive charges. What Charge: Positive (+), Negative (–), or Neutral (0)? + + ___ A positive and negative charge. ____ – –+ –+ – – – + + – – ___ – + + – + + + – ___ Two balloons on a string pushing apart. Causes an electric force and charges to move. ___ 2 protons and 4 electrons – ___ A 3 C charge and a –4C charge. – – ____ + – + – +– + ___ 18 protons and 16 electrons ___ A piece of rubber after rubbing it with fur. What are the charges of the second objects? – + Does the Electric Force increase or decrease? _____ If the distance between the charges increases? A balloon is rubbed against hair. Afterwards it sticks to a wall. A) Is the balloon attracted or repelled by the wall? B) Are the balloon and wall oppositely charged or like charged? You walk across a carpet. When you try to touch a door knob a spark jumps between you and the door knob. Why? _____ If one of the charges is bigger (increases)? _____ If both of the charges decrease (gets smaller)? _____ If the charges get closer? Two objects are charged, but do not arc. Give two ways to make them arc. A negatively charged rubber rod is brought close to the metal top of an electroscope. A) Will the electrons in the metal stay near the rod or move away from the rod? Rubber rod – – – – –– – – – Metal B) Why? C) On the diagram, draw where the electrons will go. leaves D) What will the metal leaves at the bottom do? cstephenmurray.com Electroscope An object has a charge of 4.5 C. A) Is the object positive or negative? B) Did it gain or lose electrons? C) If you touch it to ground, will it lose electrons to ground or gain electrons from ground? D) What will its charge be after it is grounded? Using the object at the right answer the following questions. A) Did it gain or lose electrons? B) When grounded, will it gain or lose electrons from ground? C) Draw a wire grounding it. D) What will its charge be after grounding? Legal copying of this worksheet requires written permission. – 8C Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9: Period: _____________________ cstephenmurray.com Legal copying of this worksheet requires written permission. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9:2 Circuits and Symbols Period: _____________________ Electricity works a lot like water. Often imagining how water would work in an circuit will tell you how electricity will work as well. Electricity flows through circuits: paths of conductors (usually wires). Any break in the circuit will cause the circuit to stop, just like a break in a pipe lets water leak out. A break in a circuit is anywhere an insulator is in the way of electricity’s flow. Paper, plastic, or even an air gap can keep electrons from flowing. + + A closed circuit has no break: electricity can flow. An open circuit has a break somewhere: electricity cannot flow. Circuit diagrams Circuit diagrams are a short-cut method of drawing circuits. They don’t need to be perfect, but they can be drawn wrong. battery Electrical Symbols Electrical Device Function Water Equivalents path for electricity to flow pipes pushes electricity through circuit pump light bulb lights up; resists electricity water wheel switch turns electricity on and off valve resistor resists flow of electricity. restriction in a pipe Symbol capacitor wire These components look similar, but are very different and have different functions. + battery light bulb resistor battery – switch The diagram on the right is a faster way of drawing the circuit on the left. (Notice the direction of the battery, which is important.) A short-circuit (also called a “short”) is a wire that by-passes a device in a circuit. Short-circuit of battery This light Electricity always chooses turns off: it is “shorted” the path of least resistance. Both lights Shortout of the Since wires have virtually no stay off. circuit. circuit resistance, electricity will go thru a wire instead of a device. This is known When a device is short-circuited the Short-circuiting a battery drains the battery as a short-circuit. current by-passes it. It is easier for the and can be dangerous. Wires could overheat, current to go thru the wire than the resistor. melting the insulation, and even cause a fire. Short Circuits Conventional Current When studying electricity, early scientists guessed that protons (+ charges) were flowing. We know now that it is the electrons that move, but it is most common to use conventional current, which follows the movement of positive charges. cstephenmurray.com What’s really happening. – – – – 6V Conventional current. + + + + 6V – – – – Legal copying of this worksheet requires written permission. + + + + Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9:2 Period: _____________________ 2. Closed circuit B. A short-hand way of drawing electrical circuits. 3. Circuit C. A circuit with a break in it; no electricity diagram will flow. 4. Voltage D. Pushes electricity through a circuit. 5. Current E. Electricity can flow through this. 6. Resistance F. The flow of electricity through a circuit. + Label the diagram: C. + D. – A. Resistor a. 2. Pipes B. Battery 3. Water wheel C. Switch 4. Resists flow D. Wire 5. Pump E. Light bulb + b. – c. d. e. A. Used to create radiant energy. 2. Battery B. Pushes electricity through the circuit. 3. Resistor C. Can turn the electricity on and off. – + – B. Valve + – 1. 1. Wires 4. Light bulb D. Allows electricity to flow. 5. Switch E. Slows down the flow of electricity. Which of the following are correct? A. Match the electrical component with the water component and diagram symbol A. Slows down the flow of electricity. 1. Open circuit A. ___________ Do all of the light bulbs light up? 1 2 C. ____________ B. ____________ Why or why not? D. ____________ 3 E. ____________ In the Lab 1) Build the following circuit, being sure to connect all components (parts) with wires. Make sure it works. Using only a battery, two wires, and a light bulb (no holder), make the light bulb light. Which of the following diagrams will light up the light bulb? + 2) Reverse the direction of the battery. Does the light still work? 3) Remove the switch. Touch the two wires between the light bulb and battery together to be sure the light still turns on. 4) Use these two wires as probes to test which of the following are conductors (C) or insulators (I). Paper _________ Plastic ________ Water_________ A Penny_______ Cloth _________ Salt Water _____ Paperclip ______ Wood ________ Sugar Water ___ Glass _________ A Dime _______ Rubber________ cstephenmurray.com A. B. – – + C. D. + + – – What two parts of a light bulb must be touched to make the light bulb light up? When the light bulb lights up, is this a closed or open circuit? What does this mean about the inside of the light bulb? When the light bulb lights up, what types of energy are used and created? Legal copying of this worksheet requires written permission. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9: Period: _____________________ cstephenmurray.com Legal copying of this worksheet requires written permission. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9:3 Current, Voltage, and Resistance Period: _____________________ Current flows through closed circuits. Current is the amount charges that flow each second . In a wire current never changes. Current can only change if there is a junction: a split or a join. Current – – – – – – – – – Devices that use more energy, use more current. More current means more electrons flowing, which is more electricity flowing (like more water flowing). A lot of current. A light bulb is brighter when it has more current going thru it. More current Electrical current is measured in Amps, which is coulombs/sec (just like gallons per sec). – – – Very little current. Voltage pushes electricity. More voltage = more current. Voltage Less current A device that uses more energy uses more current. A louder radio pulls (uses) more amps. Resistance slows down electricity. More resistance = less current. Resistance Water falls due to gravitational potential energy (Ep). Likewise, current moves because of electrical potential energy given to electrons by voltage. There must be a change (difference) of voltage for current to move. Dams hold back water. Resistors hold back electrons. Both reduce current. – – – – – – – High potential energy Adding Energy (Work) High voltage Using Energy Voltage pumps electricity, doing work to give potential electric energy (Ep) to the electrons. Batteries give voltage. The resistors use all of the electrical potential energy. This is why the voltage always equals 0 volts just before it reenters the battery. Current flows 1.5V No voltage (0 V) Zero potential energy Batteries can add together, 3 V (increasing voltage) or subtract (canceling each other out) if they are put in the circuit wrong. 1.5V Light is off 1.5 V No current 1.5V 0V 6V + Ohm’s Law Current (in amps [A]) V I= R 6V + 6V + Resistors use up voltage. With the same voltage (2 batteries), more resistance (2 bulbs) = less current (dimmer bulbs). 6V 6V Ohm’s Law can tell us the current, voltage, or resistance if the other two of them are known. Voltage (in volts [V]) Current is dependent on voltage and resistance. Resistance (in ohms [Ω]) Current can never change voltage or current, but both voltage and resistance can change current. Current equals the voltage divided by the resistance. cstephenmurray.com With the same resistance (1 bulb), more voltage (2 batteries) causes more current (brighter). 6V Just as a waterwheel slows down the falling water, resistors use the electrical potential energy to do work (something useful). Anything that uses electricity has resistance: light bulbs, speakers, etc. Regardless of the amount of resistance, all the voltage is always used up in any circuit. Increasing voltage increases current. Increasing resistance decreases current. Decreasing voltage decreases current. Decreasing resistance increases current. 6V 0 volts total – – – – Ex. How much current does a 12 V battery push through a 3 Ω resistor? V = 12 v R=3Ω I=? Legal copying of this worksheet requires written permission. I= V R = 12 v = 4A 3Ω Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9:3 Period: _____________________ 1. Voltage A. Units for voltage. 2. Current B. Slows electricity down in a circuit. 3. Resistance C. Units for current. 4. Amps D. Pushes electrons thru a circuit. 5. Ohms (Ω) E. Units for Resistance. F. 6. Volts Voltage (V), Current (I), or Resistance (R)? Amount of electricity flowing in a circuit. Which has more current flowing thru it? A loud radio or a quiet radio? A dim light bulb or a bright light bulb? A fast toy car or a slow toy car? A cold wire or a hot wire? A) ____ Flowing electrons. B) ____ Pushes electricity in circuits. C) ____ Like a water pump. D) ____ Measured in Ohms. E) ____ Measured in Amps. F) ____ A battery gives this. G) ____ Measured in volts. Which will have more resistance: an insulator or a conductor? Which resistor is the better conductor: 150Ω or 600Ω? Which resistor is the better insulator: 24Ω or 6Ω? Voltage (V), Current (I), or Resistance (R)? A _____ If you increase resistance what decreases? B. ____ If you increases voltage what increases? C. ____ If the current decreased what increased? D. _____ If current increased what increased? E. _____ If current increased what decreased? F. _____ If resistance is decreased, what increases? G. _____ More batteries will increase these two quantities. How much current does a 9V battery push thru a 3Ω resistor? Variables Equation Solve A 4 Ω resistor has 3A running thru it. Find the battery’s voltage. Equation Solve Variables 6V 6V Total voltage (VT) = 6V Total voltage (VT) = 6V An 18V battery produces 2A in the circuit. How much resistance is in the circuit? Variables Equation Solve Which of these two water towers would give the most voltage to a water circuit? Add (A) or reduce (R) voltage? When the switch is closed will the light turn on? Why or why not? Resistors? A Which light bulbs will light? (All are in closed circuits.) If it does light, draw an arrow to show the direction of current. 3V H) ___ Slows down current in a circuit. I) ___ Does work in an electric circuit. J) ___ Gives electric energy. K) ___ 12 ohms L) ___ 36 volts. M) ___ 5 amps. 3V 6V 3V 9V 0V 9V 9V With the same resistance, which battery will cause more current to flow: a 12V or a 24V battery? B H G Wires? C D F E Batteries? High, Medium, or Low voltage? Point A______ Point E______ Point D______ Point H _____ Point F ______ Point B______ Point C ______ Point G _____ A bird lands on a 20,000 volt wire. Both feet are touching. A) What voltage is the bird’s left foot? B) What voltage is the bird’s right foot? Voltage give what kind of energy to electricity? C) What is the difference of voltage between the bird’s feet? How much potential energy does water have after it falls to the ground? D) So, why can a bird land on an electrical wire and not get electrocuted? How much voltage does a circuit have just before going back thru the batteries? cstephenmurray.com Legal copying of this worksheet requires written permission. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9: Period: _____________________ cstephenmurray.com Legal copying of this worksheet requires written permission. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9:4 Types of Circuits Period: _____________________ Wires and Voltage Since wires are conductors, they have no resistance, so they have no voltage difference. Current joins Junction Series circuits have all only one path for the electricity to flow. There are no junctions. Current can split apart or join together. IT IT Total current in and out of a junction is equal. Parallel circuits have multiple paths for the electricity to flow. Junction (current splits) IT The branches (paths) of a parallel circuit are independent: if one light is unscrewed, the other will stay on. The total current equals the sum of the two branch currents. Objects in parallel have the same voltage because they share wires (same wire: same voltage). 3V 3V 2A 6V 2Ω 2A 0V 9V Vtotal = 3 V Rtotal = 8 Ω Resistors and batteries in series add together. Vtotal = 6 V Rtotal = 1 Ω Batteries in parallel share the same voltage (they just last longer). Resistors in parallel reduce total resistance because there are more paths for the current to flow. Example 1: Find the total current in this series circuit. Example 2: Find the total current in this circuit. 12 volts Step 2. Rtotal = 1 + 2 + 3 = 6 Ω (in series) R1 = 1 Ω Step 1: 12 V Vtotal = 24 volts 12 V R2 = 2 Ω Step 3: V = IR V Itotal = total Rtotal R3 = 3 Ω Itotal = cstephenmurray.com 3Ω 0V 1.5 V 0V 6V 6V 6V 1.5 V 6V 1.5 V 4V 2A Junction (current joins) When adding together batteries or resistors, it depends whether they are in series or in parallel. 8V 2A I2 I1 IT = I1 + I2 Objects in series have the same current because there is only one path. 4Ω Junction Current splits Your house is wired in parallel, so that each light and appliance can be turned on and off independently. The current is the same everywhere in a series circuit. 4A 2A Series versus Parallel If any part of a series circuit is broken, the circuit fails. The lights are dependent on one another: if either light is unscrewed both lights will turn off. IT 4A 2A wires don’t change voltage at all. 4Ω 6A 12V 12V 12V The voltage change 12V over any wire is zero. 0V 0V 0V OR The voltage is the Batteries add voltage, same everywhere resistors subtract voltage, and in the same wire. Multiple Devices Just like in a river, current can only change if there is a junction: a split or a join. Junctions 0V 24 = 4 amps 6 Step 1: Vtotal = 12 volts Step 2 : I branch 2 = 6V 6Ω 3Ω 12v = 4a 3Ω 6V 0 volts 0 volts Step 2 : I branch1 = Legal copying of this worksheet requires written permission. 12v = 2a 6Ω Step 3 : I total = I 1 + I 2 = 2 + 4 = 6a Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9:4 Period: _____________________ 1. Series A. The voltage across any wire. 1. R1 A. Voltage between A and B. 2. Short Circuit B. A circuit with multiple paths for current to flow. 2. VT B. The total voltage in the circuit. 3. Parallel C. Where current splits or joins. 3. IT C. The resistance of resistor 1. D. An independent path for electricity in a parallel circuit. 4. V2 D. The current in branch 2 of the circuit. 4. Branch 5. I2 E. Total current in the circuit. E. When a wire by-passes a part of a circuit. 6. RT F. A circuit with only one path for the 7. VAB electricity. 5. Junction 6. Zero F. The voltage of battery 2. G. The total resistance of the circuit. Are these devices in Series or Parallel? Series or Parallel Circuit? A. ______ ___ Only one path for the electricity to flow. B. ______ C. ______ D. ______ ___ Paths are dependent on each other (one affects the other). 2V ___ How your house is wired. 9V 2V 6Ω ___ Paths are independent of each other. 5Ω 4Ω 6Ω 9V ___ If one light turns off, the others stay on. VT = _____ ___ If you turn off one light, all the lights turn off. RT = _____ VT = _____ RT = _____ ___ Has more than one path for the electricity to flow. B A ___ Two devices have the same current. C ___ Two devices have the same voltage. Understanding current. Fill in the missing information on the following graphics. 6V 4Ω D 4Ω 6V 4A 3A IT = 18 A 6A ITotal = _____ I2 = _____ I = _____ 1A F G VT = ______ VFG = ______ VED = ______ VAB = ______ VFB = _______ VAC = _______ VEA = ______ VCE = ______ VDC = _______ A) What is the total voltage above? B) What is the voltage from B to F? C) What is the resistance from B to F? D) Find the current flowing from B to F (label it on the diagram). I = _____ 1A E 3A E) How much current flows from C to G (label it)? ITotal = _____ Which resistor will have more current running thru it? F) So, using D and E above, what is the total current going thru point E (this is the total current [IT])? 3V 20 Ω 5Ω G) Using VT and IT, find the total resistance of the circuit [RT]. 3V Why? Which light bulb will be brighter? cstephenmurray.com Legal copying of this worksheet requires written permission. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9: Period: _____________________ cstephenmurray.com Legal copying of this worksheet requires written permission. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9:5 Power and Voltage Drops Period: _____________________ Electrical power tells us how fast electricity is being used in a circuit or resistor. A more powerful device uses the same amount of electricity, just faster. Electrical Power Electrical Power: P = VI Power (in watts) Ex. A 12 V battery pushes 3 A thru a light bulb. How much power does the light bulb use? Voltage (in volts) Current (in amps) V = 12 v I=3A P = ____ Electrical Power equals the voltage times the current. A brighter bulb uses more power. Since P= VI, a bulb could be brighter because it uses more voltage with the same current OR because it uses more current with the same voltage. P = VI = P = 12(3) = 36 w 24 V 16V 4Ω 8V 4Ω 4A V1 = I1R1 = 4(4) = 16 V R1 uses 16 V, leaving 8 V. V2 = I2R2 = 4(2) = 8 V 8V 4A 2Ω 2Ω PT = VTIT PT = 24(4) PT = 96 w R2 uses 8 V, leaving 0 V. 0V Rtotal = 6 Ω Finding the total current and power in a parallel circuit is much easier if you think of it as two independent series circuits. Simplifying Parallel Circuits Semi-complicated For objects in parallel, the one smallest resistor uses the most current and the most power. Branch 2 Simplified Branch 1 P2 = V2I2 P2 = 8(4) P2 = 32 w 2Ω 8V Both light bulbs have the same current, but the one with more resistance is brighter because it uses more voltage and uses more power. Notice V = 8 V between the resistors. Also, the total voltage used by the resistors must equal the total voltage given by the batteries: 24 volts. V 24 IT = T = = 4A RT 6 P1 = V1I1 P1 = 16(4) P1 = 64 w 4Ω 16 V 4A 24 V 8V 8V For objects in series the biggest resistor uses the most voltage and the most power. 2. Use V = IR for each resistor. 1. Find the total current (IT). Vtotal =24V 40 W Batteries add voltage, resistors subtract voltage, and wire don’t change voltage at all. To find the voltage used by a particular resistor, you have to know the current running thru it. Voltage Drops 8V 100 W 12V 2A 6V + 4A 6V 4A 6Ω 3Ω P2 = V2I2 = 12(4) = 48 w P1 = V1I1 = 12(2) = 24 w R2 = 3 Ω Both light bulbs have the same voltage, but the one with less resistance is brighter because it has more current and uses more power (this is how your house works). V 12 I 2 = 2 = = 4A R2 3 IT = 2 + 4 = 6A + – – – – – 3. One electron enters the battery 1. Battery pushes out one electron – 2. Electrons repel each other throughout the wire – 25A – – Legal copying of this worksheet requires written permission. – – – – The electrons that move to make electricity do not come from the battery: they are already in the wires of the circuit. Metals are good conductors because their electrons can move. 1 electron in – Fuse Electricity causes heat. Fuse melt (or break) when too much current passes through them, protecting expensive electronic equipment. Like fuses, circuit breakers protect against too much current, also, but can be reset, instead of replaced. 1 electron out – – Electrons Too much current causes the thin strip of metal to melt. – V 12 I1 = 1 = = 2A R1 6 Fuses cstephenmurray.com Vtotal = 12V – R1 = 6 Ω – Vtotal = 12V Remember that devices in parallel have the same voltage, but they have different current. – = 2Α 3Ω – 6V 6Ω – – – – 3Ω 6V – 6Ω 6V – 6V Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9:5 Period: _____________________ A. An independent path in a parallel circuit. Which is brighter: a 60 W or a 100 W bulb? Which one uses more power? B. A device that breaks to protect against 2. Circuit breaker excessive current. Must be replaced. A 4 Ω and a 10 Ω light bulb are in series. Which one is brighter? C. Where branches joint or split. 3. Wire 1. Fuse 4. Branch D. Protects against high current, but can be reset. Why? 5. Power E. Where most of the electrons in a circuit come from. A 4 Ω and a 10 Ω light bulb are in parallel. Which is brighter? 6. Junction F. Why? The product of voltage and current. The electricity in your house is 120 volts. How many amps does a 60 watt light bulb use? Label the voltages at the letters. B A V at A = 1Ω 1V V at B = 1Ω 1V V at C = 1V V at D = 1Ω C D R1 = 1 Ω 9V R2 = 2 Ω How much power is used by a 120 V circuit using 6 amps? A 240 volt circuit (like your dryer) has 20 amps flowing through it. How much power is it using? VT= ________________ R T= ________________ IT = ________________ 35 amps of current goes through a 40 amp fuse. What happens? V over R1 = _____________ 3V R3 = 3 Ω V over R2 = _____________ 25 amps of current goes through a 15 amp fuse. What happens? V over R3 = _____________ Series or parallel? Which resistor uses the most power? P2Ω = ___________________ P3Ω = ___________________ B1 PT = ___________________ Why? 6V Split the following parallel circuit into two independent series circuits. B2 I1 I2 R1 = R2 = 6Ω 3Ω 6V IT 3V I1 = ________________ I2 = ________________ RT = _______________ Series or parallel? 6Ω VBranches = ___________ IT = ________________ 3V 3Ω VT = _______________ P6Ω = ______________ P3Ω = ______________ Which resistor will use more power? PT = _______________ VT = ________________ 12v 12v VBranches = ____________ R1 = R2 = 12 Ω 8Ω R3 = 8Ω I1 I2 I3 I2 = _________________ Find the current in each circuit. Find the total current. Find the total resistance. cstephenmurray.com I1 = _________________ IT Which resistor uses the most power? Legal copying of this worksheet requires written permission. I3 = _________________ IT = ________________ RT = ________________ PT = ________________ Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9: Period: _____________________ cstephenmurray.com Legal copying of this worksheet requires written permission. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9:6 Meters Period: _____________________ As the name suggests, a multimeter can act like a multitude of meters. It can be a voltmeter, ammeter, or ohmmeter, but you have to know how to use them in a circuit. Multimeters A multimeter allows you to diagnose troubleshoot) circuits or broken equipment quickly. Many people throw out items that can be easily fixed. 16V By moving the dial you select which meter it is. V A Ω Circuit Symbols for Meters Use the probes to test the circuit. V Voltmeter A Ammeter 2Ω 4Ω -- 4Ω Ω 4Ω 6Ω 2Ω 4Ω Measure resistance outside a circuit: with no battery at all or your measurements will be wrong. Must have a break An ohmmeter can measure individual resistors or multiple resistors. If a wire or resistor is broken (bad) the ohmmeter will read infinite resistance or error. Test each part of a circuit to find which part is broken. A voltmeter measures voltage (volts). A voltmeter must be in parallel like an ohmmeter, but with the circuit on. Must be a voltmeter because it is in a circuit. Circuit symbol Ohmmeter An ohmmeter measures resistance (ohms). Measure resistors outside of the circuit. Ohmmeters Voltmeters Ω 4Ω V 8v 12V A car battery only provides 12V, but a lot of amps. 0V 12V V 4V 2Ω AA, AAA, and D cell batteries read 1.5 V when new. After time the voltage drops some. Batteries also read lower when on. drained closed switch A voltmeter needs the circuit on. A voltmeter can read the voltage given by a battery or used by a resistor. Ammeters An ammeter measures current (amps). An ammeter must be in series with the circuit on. CAUTION! An ammeter is a very delicate device. Incorrect usage can badly damage the ammeter. Incorrect A voltmeter can measure a battery in the circuit or out of the circuit, while a resistor has no voltage outside of a circuit. Correct 1Α 3V 1Ω 6Ω 3V 1A 3Α 4Α cstephenmurray.com 3Ω 1.5 V A A A1 1.5 V To correctly hook up an ammeter, break the circuit where you want to read the current and place the ammeter into the break. Legal copying of this worksheet requires written permission. A2 A3 In this diagram there is only one ammeter. It has been moved to different parts of the circuit. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9:6 Period: _____________________ A. Used to measure current. 1. Voltmeter Ohmmeter, Voltmeter, or Ammeter B. Used to measure voltage. ____ Must be in series. ____ The circuit cannot connected. 3. Probes C. The parts of the meter that touches the metal of the circuit device. 4. Ammeter D. A device that can measure voltage, current, or resistance. ____ Used to tell the amount of current in the circuit. 5. Ohmmeter E. Used to measure a resistor. 2. Multimeter ____ Must be in parallel with the device being measured. ____ The circuit must be on. ____ Delicate. Can be damaged if hooked up wrong. How do you hook up an ohmmeter? ____ Can measure if a battery is worn out. ____ Can measure a resistor only in a circuit. ____ Can measure a resistor out of the circuit. How do you hook up a voltmeter? What is the resistance for a good wire? How do you hook up an ammeter? 1 M1: M2: M3: M4: M5: 3 1Ω 9Ω 6V 2Ω Draw meters that will measure the following: Identify the meters as voltmeters or ammeters. 2 3V What is the resistance for a broken wire? 4 5 ______ ______ ______ ______ ______ Figure out what each meter reads. R1 = 4 Ω M1: Total voltage M2: Total current M3: Voltage over R2 9V R2 = 2 Ω 9V R3 = 6 Ω Figure out what each meter reads. In Lab: Measure the three resistors you are given: R1 = _________ R1 = _________; R2 = _________ VFA = ________ 1.5 V Put the above resistors in series. RT = _________. How does RT compare with the individual resistors? VBE = ________ VCD = ________ 1.5 V Put the above resistors in parallel. RT = _________. How does RT compare with the individual resistors? VED = ________ R2 = _________; Build the following circuit: A VAB = ________ 1.5V VDE = ________ VEF = ________ 1.5V cstephenmurray.com C F R2 = ____ 0 G R1 = E C R2 = D F I1 = __________ Using VT and IT, calculate RT. I2 = __________ IT = __________ R3 = ____ E B WITH THE MULTIMETER OFF: set up your circuit to read the current in the first branch (at B or E). Have the teacher check your setup before you turn it on. B R1 = ____ 0 VBC = ________ VCD = ________ VEA = ________ R3 = _________. A Check it with your ohmmeter. D Legal copying of this worksheet requires written permission. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9: Period: _____________________ cstephenmurray.com Legal copying of this worksheet requires written permission. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9:7 Magnets Period: _____________________ A magnet is anything that can attract or repel another magnet. Magnet Basics Donut magnets Horseshoe magnet Bar magnets repel attract Aluminum 1) All magnets have two poles: a north and a south. 2) You can’t separate a N pole from a S pole (you just make smaller magnets). Opposite attract 3) Magnets exert magnetic forces of attraction and repulsion. N e- N Temporary magnets become magnets only when near a permanent magnet. The spinning electrons line up together when a magnet is near, but will eventually fall back after the magnet leaves. Only ferrous materials can become temporary magnets. Often bumping them (like dropping) can cause the electrons to fall back quickly. S An electromagnet is a magnet made by moving electricity. Electromagnets Ways to strengthen an electromagnet: Electromagnets are particularly useful because they allow us to create forces that we can turn on and off at will. 2) More coils (the easiest way to add electricity). 1) More electricity (more current thru more batteries, etc). A toaster holds the toast down with an electromagnet. When the electricity turns off, the electromagnet releases the toast. 3) Add a ferrous core, especially iron, which becomes a temporary magnet. An electromagnet does not have to have a core: any loops of electricity will make an electromagnet. Generators and Motors Moving electricity creates magnetic fields. Moving magnets make electricity. Because electricity and magnetism are linked we can make motors and generators. Generators generate electricity. Something turns the generator (does work) causing magnets to move, which creates electricity. Dams, cars, and power plants all produce electricity in this way. Motors use electricity. Electricity causes magnetic forces thru electromagnets. The electromagnets cause the object to turn (do work). Work in (air): electricity out. cstephenmurray.com 4) Magnets only attract ferrous metals: Iron, Cobalt, and Nickel (steel is an alloy of mostly Iron and Nickel). Permanent magnets do not lose their magnetism. Many of the electrons in a permanent magnet are spinning the same way and the all of the little electromagnets add up. Lodestone and Magnetite are the only two natural permanent magnetic materials. How do Magnets Work? Moving or spinning electrons in atoms cause magnetism. If electrons are paired and spinning in opposite directions, the magnets cancel each other out. When a substance is magnetic many of the electrons are spinning in the same direction. Likes repel el Ste Electricity in: work out (moving air). Legal copying of this worksheet requires written permission. Motor or Generator? It could be either one, depending on how it is used. Any motor can create electricity and any generator will turn if electricity is applied. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9:7 Period: _____________________ Permanent magnet A. Turns when electricity is turned on. 2. Temporary magnet 3. Motor C. Becomes a magnet when electricity moves in wire coils. 4. Generator D. Uses work to make electricity. 5. Core 6. Electromagnet E. Does not lose its magnetism: lodestone and magnetite are only natural types. F. Center of the electromagnet coils. N S ___ ___ ___ If the three magnets are attracting each other, label N and S on the second magnet. N S ___ ___ If the two magnets are repelling each other, label N and S on the second magnet. ___ Attract or repel? Attract or repel? The diagram show magnetic levitation (Maglev). The top bar magnet is suspended (floating) above the bottom magnet while in a graduated cylinder to keep it from falling to the side. 1) Two keep the upper magnet levitated, are they attracting or repelling each other? 2) Label N and S on the upper magnet. ___ ___ N B. Becomes a magnet near a magnet, then loses its magnetism when moved away. S 1. True or false (and why): “A magnet will pick up any piece of metal.” 1) Label the north and south poles of the nail magnet. 2) Will the nail stay a magnet when removed from the bar magnet? 3) Is the nail a temporary or permanent magnet? What makes a magnet on the atomic level? As a magnet gets closer to another magnet, does the magnetic force increase or decrease? Draw a simple electromagnet: Motor, Generator, or Both? _____ Creates electricity. _____ Has loops of wire in it. _____ Creates motion. _____ Is turned by a force. _____ Can make electricity. _____ Work _____Used in a hydroelectric dam. _____Used in open or close windows in a car. _____Turns when electricity is applied to it. Electricity Name three ways you could increase the strength of an electromagnet: Which electromagnet is stronger? A or B? A. 9V B. 9V C. 9V D. 3V B or C? C or D? A or C? _____ Electricity Work A or D? Which is the strongest of the four? cstephenmurray.com Legal copying of this worksheet requires written permission. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9: Period: _____________________ cstephenmurray.com Legal copying of this worksheet requires written permission. Copyright © 2007, C. Stephen Murray Name: _____________________ Period: _____________________ Unit 9:8 Electricity and Magnetism Review 1. Voltage A. 8 amps 1. Current A. A path for electricity to flow. 2. Resistance B. 8 volts 2. Voltage B. A material that allows electricity to flow. 3. Power C. 8 coulombs 3. Resistance 4. Charge D. 8 watts 4. Insulator 5. Current E. 8 ohms 5. Conductor E. What pushes electricity in a circuit. 6. Circuit F. What moves: electrons or protons? Why? D. Slows down electricity The flow of electrons thru wires. A _______________ allows electricity or heat to pass through it. An object has a charge of –8 C. A) Is the object positive or negative? B) Did it gain or lose electrons? C) If you touch it to ground, will it lose electrons to ground or gain electrons from ground? D) What will its charge be after it is grounded? What are the charges of the second objects? Electricity flows through paths called ___________. A _________ circuit has no breaks in it, while an ___________ circuit has a break and stops the flow of electricity. An ________________ will not allow electricity to pass. Electricity is made up of flowing ______________. Like electric charges attract/repel. Opposite charges attract/ repel. – + Draw a circuit of two batteries, a light bulb, a resistor, and a switch, all in series. Repel Attract C. A material that resists electricity. What is electricity? Will electrons flow between the two objects? B. A. 5C 0C -3C -3C -2C -6C Why does electricity move? You have two light bulbs and a battery in a circuit. If you add another battery, do the light bulbs get brighter or dimmer? Why? What is arcing? You have two light bulbs and a battery in a circuit. If you add another light bulb, do the light bulbs get brighter or dimmer? Why? When and why does arcing occur? If a 12 v battery is connected to a 24 Ω resistor, how much current is flowing? How much voltage is needed to produce 2 amps through a 4 ohm light bulb? Increases (I) Or Decreases (D) Increasing resistance _______ current Decreasing resistance ______ current Increasing voltage ______ current Decreasing voltage ______ current How can you tell if two light bulbs are in parallel? How can you tell if two light bulbs are in series? If a light bulb in your house (120 V) draws 0.5 amps, how much power does it use? cstephenmurray.com Is your house wired in series or in parallel? Why? Legal copying of this worksheet requires written permission. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9:8 Period: _____________________ What is the change of voltage across a wire? What happens when you short circuit one light bulb in a two light bulb circuit? Why can a bird sit on a wire and not be electrocuted? What happens if you short circuit a battery? Fill in the missing information on the following graphics. Where do most of the electrons come from that run thru a circuit? 2Ω 5A 6V 3A 4Ω 3V B VT = R1 = 10 Ω 3V VT = _____ RT = _____ IT = _____ R2 = 5Ω 6V R3 = 3 Ω Series or parallel? ___________________ RT = ___________________ IT = ___________________ IR3 = ___________________ VR2 = ___________________ PT = ___________________ N ___ ___ ___ ___ The three magnets are repelling each other. Fill in the missing information. A S ___ ___ ___ ___ The two magnets are attracting each other. Fill in the missing information. Series or parallel? I1= C D I2= I3= 6V R1 = 2Ω 6V 6V G H R3 = 1Ω R2 = 3Ω F E VT = _________________ I2 = __________________ VDF = _________________ I3 = _________________ VHG = ________________ IT = __________________ Vat F = ________________ RT = _________________ I1 = ___________________ PT = _________________ Someone asks you how what a circuit is and how it works. Tell them. What will a magnet attract? What are fuses and circuit breakers? What will a magnet repel? How are they different? What does moving electricity cause? What do moving magnets cause? What is a motor? What is an electromagnet? How does it work? How do you strengthen an electromagnet? What is a generator? How does it work? cstephenmurray.com Legal copying of this worksheet requires written permission. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9: Period: _____________________ cstephenmurray.com Legal copying of this worksheet requires written permission. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9: Period: _____________________ cstephenmurray.com Legal copying of this worksheet requires written permission. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9:S1 Lab: How Bright is the Light? Period: _____________________ Purpose: To investigate how voltage and resistance affect the brightness of a light bulb in a circuit. Background: Students should know that a battery is a source of voltage. More batteries = more voltage A light bulb causes resistance in a circuit. More light bulbs = more resistance The brightness of the light bulb increases as the current through the light bulb increases. Materials and Preparation: Have 2 batteries, 2 light bulbs, wires/alligator clamps or a spring board per set-up. Electrical tape and Christmas lights offer an easy and inexpensive alternative to regular light bulbs. Effect of changing voltage on light bulb brightness: Circuit # light bulbs # batteries 1 1 1 2 1 2 3 1 3 relative brightness Effect of changing resistance on light bulb brightness: Circuit # light bulbs # batteries 1 1 2 2 2 2 3 3 2 relative brightness Student OutcomeWrite a scientific statement to explain the effect of voltage and resistance on the brightness of a bulb. cstephenmurray.com Legal copying of this worksheet requires written permission. Copyright © 2007, C. Stephen Murray Name: _____________________ Unit 9: Period: _____________________ Curriculum Notes: 1. MOST IMPORTANT DEMO. I have tried numerous ways for students to understand how voltage, resistance, and current relate. I have had them take measurements for themselves. The problem is that they take the measurement at different moments in time. They do not accept that the current is the same everywhere in a series circuit. So, make the following circuit: Any resistor that allows enough current. Variable power supply 2. Variable resistor By putting multiple multimeters in the circuit you can PROVE that the current is the same everywhere because they will all read same amount!!! You can change the voltage and the resistance, but all multimeters will always read the same current. It is also a good demo of how voltage and resistance affect current. V Concept Key—Series circuits. Spend more time on series circuits before moving onto parallel circuits. For years my students have struggled with calculating voltage drops around a series circuit. This last year I used the above demo and spent more time with just series circuits and they got it. And the just to parallel circuits was easy. I had almost 100% comprehension with both circuit types and even with compound circuits. cstephenmurray.com Legal copying of this worksheet requires written permission. Copyright © 2007, C. Stephen Murray
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