Upcoming SlideShare
×

# Electricity pale

1,226 views

Published on

0 Likes
Statistics
Notes
• Full Name
Comment goes here.

Are you sure you want to Yes No
Your message goes here
• Be the first to comment

• Be the first to like this

Views
Total views
1,226
On SlideShare
0
From Embeds
0
Number of Embeds
9
Actions
Shares
0
29
0
Likes
0
Embeds 0
No embeds

No notes for slide

### Electricity pale

1. 1. 198 199SUBJECT: TECHNOLOGYTITLE OF THE UNIT: ELECTRICITYAGE OF STUDENTS AND LEVEL: 14 YEARS/ 3º ESOSTUDENTS´ LANGUAGE LEVEL: A1/A2BRIEF DESCRIPTION OF UNIT AND NUMBER OF SESSIONS:Electricity is the main unit of 3rd ESO. The objective of the unit is that students know whatelectricity is, its effects and its environmental impact. They should learn to mount and analysesome basic circuits, both in the workshop and using some simulation program.Students have never seen electricity before in secondary school. Due to the importance ofelectricity nowadays, we think that the teacher should dedicate a whole term to this unit.AIMS:– To introduce electricity to the students.– To understand the difference between conductors and insulators.– To identify the components of an electric circuit and its symbols.– To acquire the concept of electrical current as well as the other electrical magnitudes.– To measure electrical magnitudes with the help of a tester/multimeter– To know the relationship between resistance and current.– To distinguish the different types of electrical circuits– To use electricity in a safe way– To be conscious of the environmental impact of electricity– To draw and analyse some circuits using a simulation program– To mount some circuits in the workshopASSESSMENT: IT’S BUILT INTO THE UNITCOMMENTS:Depending on the available time and resources in the workshop, the teacher will decide on thenumber of exercises and practices to be done.
2. 2. 1. INTRODUCTIONElectricity completely surrounds us. For most of us, modern life would be impossible without it.Here are just a few examples: – Throughout your house, you probably have electrical outlets where you can plug in all sorts of electrical appliances. – Most portable devices contain batteries, which produce varying amounts of electricity depending on their size. – During a thunderstorm, there are huge bolts of electricity called lightning that shoot down from the sky. –It is easy to create electricity from sunlight using a solar cell; or you can create electricity from the chemical energy in hydrogen and oxygen using a fuel cell.It is hard to imagine modern people living without electricity.Matter is made up of atoms. Atoms contain particles called: protons, electrons and neutrons. – Protons have a positive charge – Electrons have a negative charge – Neutrons have no chargeElectrons are a fundamental part of electricity. In many materials, electrons can move from oneatom to another. This movement of electrons is the origin of electricity, in fact the movement ofelectrons is an electric current.If the electrons don’t move, the material doesn’t conduct electricity and it is called an insulator.Some materials which are electrical insulators are for example: wood, plastic, glass, pottery…If the electrons can move through the material, it is an electrical conductor. For example, waterand metals such us gold, silver, copper, iron: – Copper is used for connecting wires. – Nichrome has more resistance and is used in the heating elements of electric fires.Electrical circuits can be complex. But at the simplest level, you always have the source ofelectricity (a battery, etc.), a device that uses it (a light bulb, motor, etc.), and two wires to carryelectricity between the battery and the load.However, electricity can be very dangerous, too. Accidental contact with electrical currents cancause injury, fire, extensive damage and even death. It is important to remember that workingwith and around electricity requires your full attention and respect.Most electricity comes from power stations that burn “fossil fuels” such as coal. The heat boilswater into steam, and the steam drives big turbines that generate electricity.But there are big problems with this way of generating electricity. Burning fossil fuels is very badfor the environment, as it creates pollution and affects the climate of the Earth. Fossil fuels arealso running out. We all need to cut down on the amount of electricity we use at the moment.
3. 3. 200 2012. EFFECTS OF ELECTRICITYElectricity is a strong invisible force that gives power to machinery, lights, heaters and many otherforms of equipment.Moving electrons have energy. As the electrons move from one point to another, this energy canprovide: – Heat: when the electrical current flows through a material, it heats. Toasters, hair dryers and space heaters turn electricity into heat. – Light: an electric current flowing through a material increases its temperature and produces light. In an incandescent lamp, for example, the energy of the electrons is used to create heat, and the heat in turn creates light. Fluorescent lamps, LEDs (Light Emitting Diodes), etc. turn electricity into light. – Movement: Electric motors turn electricity into motion. – Sound: Speakers turn electricity into sound waves. – Information: Computers turn electricity into information. Telephones turn electricity into communication. TVs turn electricity into moving pictures. Radios turn electricity into electromagnetic waves that can travel millions of miles.3. ELECTRIC CIRCUITSAn electric circuit is an unbroken path along which an electric current exists or is able to flow.3.1. COMPONENTS OF AN ELECTRIC CIRCUITThe basic components of a circuit are:ConductorsThese are the wires that connect thedifferent elements of the circuit whichallow the flow of electricity. The wires areusually made of copper and covered withplastic in order to isolate them.
4. 4. Power supplyThis is a device that causes energy to flow through the circuit. A battery, a generator or analternator are examples of power supplies. All of them transform a type of energy into electricalenergy.Batteries are used in small devices. They transform chemical energy into electrical energy.There are different kinds, for example:– Normal batteries, which are the mostcommonly used.– Alkaline batteries, which last longer.– Rechargeable batteries, which can berecharged several times.– Button batteries, which are smaller butpollute the most.All batteries contain toxic materials so they can not be thrown into the rubbish. There arespecial containers for collecting and recycling used batteries.Generators or alternators, which produce electrical energy in electrical power stations.Output devices: AppliancesThese elements receive electrical energy and transform it into other types of useful energy(light, heat, movement, sound, etc.). A bulb, a heater, a motor or a bell are some examples ofappliances.– Bulbs: they transform electrical energy into light.– Motors: they transform electrical energy intomovement.– Bells: they transform electrical energy into sound.– Heaters: they transform electrical energy into heat.Control elementsThese elements are used to control circuits. You canuse them to open, close and switch between differentcircuits. There are different kinds such us push buttonswitch, on-off switch, 2-way switch, etc.Circuit protection elementsIf too much electrical current passes through a wire,it heats up and a fire can start. To avoid this, mostelectrical circuits, including those in houses, use fuses(as shown in the figure on the right). A fuse is a device-normally a wire- that burns up and breaks if toomuch electricity goes through it. The element in thefuse melts, breaking the circuit and preventing othercomponents of the circuit from being damaged by theovercurrent.
5. 5. 202 203To establish an electric circuit there must be two requirements: 1. A closed path for the electrons to flow. 2. An energy supply which creates an electric potential difference across the two ends of the electrical circuit. The electric potential difference is the force that causes the current to flow.With only these two requirements we get a short circuit. The charge flows between the terminalsand a lot of energy is consumed. The circuit heats the wire to a high temperature and a fire mightbreak out.In practice, electrical circuits are designed to serve a useful function. So the circuit must have abulb, a motor, a bell or a similar device that uses electricity for a specific function.3.2. SYMBOLS OF ELECTRIC COMPONENTSSchemes are used to represent electrical circuits in which each element is identified by a symbol. G conductor cell battery generator switch push switch two way switch bulb M V A resistor motor volmeter ammeterHere you can see an example of an electrical circuit, containing some of these elements: + 9V 13A
6. 6. 4. ELECTRICAL MAGNITUDES4.1. TENSION OR VOLTAGE (V)Voltage is the force that causes a current to flow. It is a measurement of the level of the electricalenergy. Voltage is measured in volts (V).For example: – A small battery used in an alarm clock has 1.5 volts. – A button battery, as in a watch, can have 3 volts. – Electricity at home is supplied at 230 volts.For a flow of current there must be a different energy level between two points of the circuit(voltage). A generator is the device that produces the voltage needed in a particular circuit.4.2. CURRENT (I)Current is the number of electrons flowing through a circuit in a second. It’s measured in amperes (A).4.3. RESISTANCE (R)Resistance is anything which opposes the flow of current in a circuit. The resistance is measuredin ohms (_)For example: – Longer wires have greater resistance. – Resistance increases as the cross-sectional area of the wire decreases. – Electrical insulators offer a very high resistance. – Electrical conductors offer very low resistance. – As the temperature increases the resistance of a wire increases (this is used in a resistance thermometer). – Resistors can be used to control the current in a circuit. – A variable resistor is used to adjust the flow of current in a circuit.5. OHM’S LAWThe relationship between current, voltage and resistance was discovered by George Ohm. Fromexperiments, he found that: V =I RThis expression can also be written in other ways: V V R= I= I RLooking at the last equation we can see that if the voltage increases, but the resistance is constant,the current also increases.
7. 7. 204 2056. TYPES OF CIRCUITSCircuits exist in all kinds of different places. The lighting in school or at home, street lights, torchesand alarm systems all have circuits that are fairly simple.Circuits are found in calculators, computers, televisions, radios, cars, medical equipment, aircraft,the Internet, factories, telephones and many more places.We shall look at some of these connections.6.1. SERIES CIRCUITComponents that are placed one after another in the circuit are connected in series. The currentthat flows across each component has the same value.The diagram on the right shows a circuit with +two lamps connected in series. If one lampbreaks, the other lamp will not light.This circuit is another example of a series Mcircuit. Different types of components can beconnected in series. + – 10K6.2. PARALLEL CIRCUITIf we connect several electric components +as shown in the figure on the right, we say 9V 10K Mthat they are connected in parallel.The scheme on the right shows a circuit +with two lamps connected in parallel. Ifone lamp breaks, the other lamp will stilllight.
8. 8. SERIES CIRCUIT PARALLEL CIRCUITScheme of R R RTotal = R1 + R2 2 1the circuit + – V R1 R2 V 1 1 1 = + RTotal R1 R2 I Total = I1 + I 2 RTotal = R1 + R2 R =R +RResistance The effect is to add more The effect isTotalreduce the resistance to 1 2 resistance to the circuit of the circuit 1 1 1 VTotal = V1 = V2 1 = 1 + 1 RTotal = R1 + R2 RTotal = R1 + R2 RTotal R1 R2 I1 = I = I1 1 of = 1 + 2 I =I +IVoltage The voltageTotalthe supply is shared I Total I1 + I 2 The voltage Total =each component across 1 RTotal R1 R2 between the components in series in parallel, is the same 2 VTotal = V1 + V2 I Total = I1 + I 2 VTotal = V1 = V2 RTotal R + R VTotal = V11 = V22Current The current that flows across each The current1 shared1between each I Total = I = I 1 is = 1 + 2 VTotal = V1 = V2 I Total = I 1 = Iparallel component connected in series is component connected in R 2 RTotal R1 2 the same I Total = I 1 = I 2 VTotal = V1 + V2 I Total I 1 + I VTotal = V1 V22 VTotal = V1 + V2 VTotal = V1 = V2 I Total = I 1 = I 2 VTotal = V1 + V2
9. 9. 206 207EXAMPLES OF CIRCUITS: SERIES CIRCUIT R1=2 R2=4 R3=6 +V=12V RTotal = 2 + 4 + 6 = 12Ω VTotal 12V I Total = = = 1A RTotal 12Ω V1 = I TOT * R1 = 1A * 2Ω = 2V V 2 = I TOT * R2 = 1A * 4Ω = 4V V3 = I TOT * R3 = 1A * 6Ω = 6V VTOT = V1 + V 2 + V3 = 2V + 4V + 6V = 12V
10. 10. EXAMPLES OF CIRCUITS: PARALLEL CIRCUIT +V=12V R1=2 R2=4 R3=6 1 1 1 1 6 + 3 + 2 11 = + + = = R Total 2 4 6 12 12 12 RTotal = Ω 11 VTotal 12V I Total = = = 11 A RTotal 12 Ω 11 V1 =V2 =V3 = 12 V V1 12V V2 12V V3 12VI1 = = = 6A I2 = = = 3A I3 = = = 2A R1 2Ω R2 4Ω R 3 6Ω I TOT = I 1 + I 2 + I 3 = 6 A + 3 A + 2 A = 11 A
11. 11. 208 209 SERIES CIRCUIT PARALLEL CIRCUIT The total resistance is smallerResistance The total resistance is greater than than the smallest of the resistancerules every single resistance of the circuit connected in parallel. The current is the same in every The sum of currents approaching point of the circuit a junction is the same as the oneCurrent As the number of appliances leaving that junctionrules increases in the circuit, the More current goes through the resistance gets larger and the easier path (the one with less current gets smaller resistance) The total voltage is shared between Appliances in parallel receive the all the appliances of the circuit. same voltageVoltage A battery voltage is equal to Battery voltage is equal to therules the sum of the voltages at every voltage at every appliance of the appliance of the circuit circuit.6.3. MIXED CIRCUITIf a circuit has components connected both in series and in parallel, we call it a mixed circuit. + – M6.4. ASSOCIATION OF BATTERIESCells and batteries are useful sources of electricity. They transfer chemical energy to electricalenergy.A zinc-carbon cell (dry Leclaché cell): This is the common cell used in torches. The voltage acrossthe cell is 1.5V. Once the chemicals are used up you throw it away.There are also re-chargeable batteries. For example, a lead-acid battery in a car turns the startermotor and is then re-charged when the engine is running. During re-charging, the energy is storedin the battery.We shall look at some ways of connecting batteries.
12. 12. Batteries in seriesWhen we connect several batteries in series in a circuit, the total voltage increases and thecurrent gets larger. AIn circuits A and B, the C 1,5batteries give 1.5 volts. volt 1,5 Volt lamp 1,5In circuit C the batteries, voltconnected in series, give 3 B 1,5 Volt lampvolts. The lamp will be very 1,5 voltbright. 1,5 1,5 volt volt 1,5 Volt lampBatteries in parallelWhen batteries are connected in parallel, as we can see in circuit B, their voltages don’t add up.The reason for connecting batteries in parallel is that two batteries last longer than one andcan supply a higher current if needed.As we can see, in circuit B, the batteries give 1.5 volts. The lamp will have normal brightness (asin circuit A) but the batteries will last twice as long as those in circuit A.7. MEASUREMENT OF ELECTRICAL MAGNITUDES7.1. CURRENT INTENSITY – AMMETERAn ammeter is an instrument which is used to measure the flow of an electric current in a circuit. e ammeter is in series with the lamp A
13. 13. 210 211Diagrams A and B below show a circuit before and after connecting an ammeter.A B ammeter I A R1 R1 R2 V R2 V – The ammeter must be connected in series with the resistor. – Ammeters must have a LOW resistance.All the current flowing in the circuit must pass through the ammeter. As meters are not supposed toalter the behaviour of the circuit, or at least not significantly, the ammeter must have a very LOWresistance.7.2. VOLTAGE – VOLTMETERA voltmeter is an instrument used for measuring the voltage between two points in an electriccircuit. e voltimeter is in parallel with the lamp V
14. 14. Diagram C shows the same circuit after connecting a voltmeter:A C I I R1 R1 voltmeter R2 V R2 V – To measure the voltage, the circuit is not changed: the voltmeter is connected in parallel. – Voltmeters must have a HIGH resistance.This time, you do not need to break the circuit. The voltmeter is connected in parallel, so it shouldtake as little current from the circuit as possible. In other words, a voltmeter should have a very HIGHresistance.Voltage measurements are used much more often than current measurements.7.3. RESISTANCE – OHMMETERAn ohmmeter is an instrument used to measure the resistance of a particular component of anelectric circuit. I I R1 R1 ohmmeter R2 R2 V
15. 15. 212 213To measure resistance, the component must be removed from the circuit.If you want to measure the resistance of a particular component, you must take it out of the circuitand test it separately, as shown in diagram D. A multimeter or a multitester is an electronic measuring instrument that combines several functions in one unit. The most basic instruments include an ammeter, voltmeter, and ohmmeter.8. ELECTRICAL SAFETYElectricity can light lamps, can work televisions and many other things we use in our everydaylife but it is important not to get in the way of electricity because it can harm you. Electricity canbe dangerous, we need to take care and keep ourselves safe. If you come into contact with theelectricity in an appliance, power cord, or power line, you could be seriously injured or killed.Here are some safety rules to help us: – Respect the power of electricity. – Never put anything into sockets. – If you use an adaptor be careful not to overload the socket. – Never poke anything into electrical machines. – Never play with electrical cords, wires, switches, or plugs. – If a plug or switch becomes hot in use turn it off. – If an appliance works improperly or gives the slightest warning of a problem, such as shocks or sparks, disconnect it and have it serviced. – Never repair a break in an outdoor extension cord. Throw the cord away and buy a new one. – Protect cords from heat, chemicals and oil. Coil cords loosely when storing tools. If cords are broken, get new ones or shorten them. – Keep cords out of pedestrian areas where people could trip over them. – Don’t use appliances with a frayed flex or a cracked plug. Tell an adult about it.
16. 16. – Never use a hairdryer or play an electrical radio or television in the bathroom or use them near any water. – Make sure your hands are dry before you touch anything electrical. – Never throw water on an electrical fire. – Stay away from power equipment. – Stay away from broken power lines. Tell an adult. – Take extra precautions when using power tools. Your electrical wiring should be adequate for the job. Circuits should be grounded. The tools should be insulated. – If you encounter an electrical-injured victim, do not touch the person until they have been freed from the source of electricity. You can use a non-conductor, such dry rope or wood to push or pull the victim away from the power source. – Stay away from substations and transformers. – Inform your teacher of faulty equipment in the workshop ELECTRICITY KILLS MAKE SURE IT’S SAFE Umatilla Electric Cooperative © Copyright 2005 - 2007 Umatilla Electric9. ELECTRICITY AND ENVIRONMENTThe generation and use of electricity affects the environment. Engineers and scientists aredeveloping new environmentally-friendly ways of generating electricity. There are lots of ideassuch as: nuclear power, wind power, solar power, wave power, tidal power, and biomass energy.Below we can see some examples of the environmental impact of electricity, both of its generationand its use: – The variety of fuels - coal, oil or natural gas - used to generate electricity has some impact on the environment. The fossil fuels are burned to create steam. This steam is used to turn a turbine which will move the electric generator. The smoke and gas from burning fossil fuels pollutes the air. For example: sulphur dioxide and NOx emissions contribute to acid rain and carbon emissions contribute to global climate change. – The force of water —used in a hydro–electric facility— to turn the turbines and the generator disrupts the natural flow of a river with negative effects on fish and water plants. – Nuclear power plants are generating and accumulating radioactive waste. – Some of the renewable energy facilities can affect wildlife (fish and birds) and the disruption of land uses
17. 17. 214 215As electricity is very important in our daily lives, we demand more electricity everyday and we arepolluting and increasing the damage to our environment. We must avoid this by using electricityefficiently and obtaining it from the cleanest sources available.There are also some things we can do to save energy in order not only to preserve the world butalso to save money, such us: – Insulate your walls, windows and ceilings. – Set your clothes washer to the warm or cold water setting, not hot. – Make sure your dishwasher and washing machine are full when you run them and use the energy saving setting, if available. – Select the most energy-efficient models when you replace your old appliances. – Be careful not to overheat or overcool rooms. – Buy energy-efficient compact fluorescent bulbs for your most-used lights. – Whenever possible, walk, bike, car pool, or use mass transit. – Reduce the amount of waste you produce by buying minimally packaged goods, choosing reusable products over disposable ones, and recycling.10. EXERCISESThe following exercises can be done with our pupils during the lessons:1. Say which of the following materials are good conductors: rubber, copper, nylon, glass, iron andwood.2. Complete the following sentences: a. The force that is applied to a conductor to cause a current to flow is _______________ b. With an increase of length or a decrease of cross-section of a conductor the resistance ________________ c. Current must always be expressed in _________________ d. The total current of a simple circuit with a voltage supply of 12 volts and a resistance of 24 _ is _________ e. When you have three bulbs connected in series, the same______________ will flow through all of them. f. When a lamp breaks and others continue working, they are connected in ______________3. A current of 3 A, flows through a resistor of 6_ .What is the voltage across R?4. What is the resistance of a circuit that is crossed by a current of 2 A with a voltage of 40 V?5. In a circuit R=2 _. What will the current flowing through it be if the voltage is 60 V?
18. 18. 6. How are the bulbs connected in each of these circuits? a) c) + + b) d) + +7. In these drawings there are various connections between bulbs and motors and one or morebatteries. Say which circuits will work and describe what will happen in each case. M + + – – + + + – – – M
19. 19. 216 2178. What is the difference between these two circuits? Which is right? Why? + – M + – M9. Which of these are electrical appliances? Torch Book Radio Mobile phone Lamp Computer Television Plastic cup10. Can you fill the gaps with the words listed? batteries safer mains water dangerousElectrical appliances run on mains or………………………or sometimes both. The mains supplyof electricity is very ………………………Batteries are usually……………than the ……………Neverlet……………near electrical appliances.11. Match the words in the first column to the best available answer in the second column: Switch 1) Energy source for a circuit 2) Measures the potential difference across any two points Battery of a circuit Resistor 3) Ratio of potential energy to current Voltmeter 4) Potential energy per unit of charge Ammeter 5) Converts electric energy into other forms Potential 6) A device for closing and opening a circuit Difference Current 7) Measures the current flowing through a circuit Resistance 8) A flow of electric charge
20. 20. 12. Match the symbols with their names: Resistor Motor Battery M Two way switch Fuse + – Bulb13. What would happen in this circuit if: I1 Ma) The motor blowsb) Bulb 1 blows + I2c) Bulb 2 blows - B2d) You open or close switch 1e) You open or close switch 214. In each of the two circuits indicate which bulb will be lit if: a. You close all of the switches except switch A b. You close all of the switches except switch B c. You close all of the switches except switch C A A B C + C – + B –
21. 21. 218 21915. Calculate the amount of current flowing through the following circuits: 1,5 1,5 5 20 R1 R2 R1 R2 + +12V 100V – –16. Calculate the total resistance and the total current which flows through the circuit in thefollowing examples:12 volts 24 volts + R1 R2 + R1 R2 – 5 10 – 10 15 R1 20 R3 10 9 volts + R2 30 –
22. 22. 11. SIMULATION PRACTICESCrocodile program, draw and analyse the following circuits, noting whether it is a series circuit, aparallel circuit or a mixed circuit. Note also the current intensity (I) flowing through each resistorand the voltage (V) across each of them. 1k 2k +6V 1k 1k 2k +6V 1k 1k 2k 1k +9V 2k 1k 2k +9V 60 +6V 40 150
23. 23. 220 22112. WORKSHOP PRACTICESHere there are some circuits that can be mounted in the workshop. The teacher will prepare somequestions for each circuit that the students will have to answer. 6V 6V + - + - L1 L2 6V 6V L1 + - + - L1 L2 L2 L3 6V 6V + - + -
24. 24. 13. ASSESSMENTTYPE 1Name:Date:NOTE: Don’t forget to use the units when needed.1. For the circuit below, calculate the current intensity flowing through the resistor (1.5 points) 10 V 150 + V 10 - 150 + - 10 V 150 + -2. What resistance must we place in this circuit if I=2 mA (1.5 points) 12 V + V 12 - + - 12 V + - 10 103. Write what kind of circuit is the one below. Calculate the current intensity flowing through 10 10each resistor. How much voltage is there in the first resistor? (1.5 points) 10 10 10 V 20 + V 10 - 20 + - 10 V 20 + -
25. 25. 222 2234. Note what kind of circuit is the one below. Write the voltage and current intensity for eachlamp. (1.5 points)Note: You can assume that both lamps similar. 0,018 A Lamp 1 Lamp 2 + 9V V – I5. Draw the scheme of a circuit with 2 lamps and 2 motors, so that: (1.5 points) a. Both lamps turn on and off at the same time b. Motors work independently from the lamps (it doesn’t matter if the lamps are on or off) c. The complete circuit can be turned off with a switch6. Write the units of the following electrical magnitudes: (1 point) a. Voltage, V: b. Current intensity, I: c. Resistance, R:7. Look at the scheme and complete the following sentences:To have both bulbs on, you shouldThe motor works ifIs it possible to have only one bulb on? Why/Why not? (1.5 points) S1 + 9V – S2 M S3
26. 26. TYPE 2Name:Year: Date:1. Draw the symbol of the following electric components: Switch Two way switch Push button switch Fuse Battery Motor Bulb Resistor Bell or buzzer Voltmeter2. How can you join 3 batteries of 1,5 volts to have a 4,5 V battery? Draw the scheme.3. How can we join three 1,5 V batteries so that they together last 3 times more than only one?4. Write the voltage that these voltmeters indicate. Don’t forget to write the units. Voltmeter Voltage V2 V3 µV µV V1 V2 + 12 V V1 µV V3
27. 27. 224 2255. Write the current intensities that these ammeters indicate. Don’t forget to write the units. A2 0.00 Ammeter Intensity µA A1 0.00 µA A1 60mA + A3 0.00 9V A2 µA A36. How much current intensity flows through these circuits when we close the switches? 9V 9V 9V + - + - + - 277. How can you make sure that a DC motor turns clockwise and then anticlockwise?