Electricity
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Electricity

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Electricity Electricity Presentation Transcript

  • Electricity Introductory Physics Canadian AcademyImage from: http://www.penguintutor.com/electronics/electrical-safety
  • Electricity Unit Questions: “How can we power a community?” Enduring Understandings: • Electricity can be harnessed for the benefit of humans Areas of interaction: Human Ingenuity The development of electrical technologies revolutionised culture Environments Can we maximise efficiency in order to maximise sustainability?Criterion Assessment TasksB: Knowledge & Formaive: Current Elecricity FlipbookUnderstanding
  • Electrostatics – Whaddya Know? Think, share, scribble it on a whiteboard.
  • Draw an Atom! What are the names, sizes, charges and positions of the components? What is the relevance of this to electricity?
  • Discover electrostatics demonstrations Try these demonstrations with your group and keep notes on the sheets provided. Can you explain your observations? Use the resources on the GoogleSite if you need to. • Electrification • Charged tapes • Balloon tricks • Opposite sides of an acrylic sheet • Triboelectric series • Electroscopes Image: balloon static from http://www.education.com/science-fair/article/physics_pickup/ Image: simple electroscope from http://www.school-for-champions.com/science/static_detection.htm Image: balloon & water from http://www.thenakedscientists.com/HTML/content/kitchenscience/exp/bending-water-static-attraction/
  • Can you explain what’s happening?Try this visualisation from PhET Labs.http://phet.colorado.edu/en/simulation/balloonsFind out more about the triboelectric series.Do electrons move from the balloon to thejumper or the other way round – why? What is happening in the electroscope? What happens when the leaves get ‘stuck’ apart? How could you get them to go back to their original positions? Why does this work? Image: simple electroscope from http://www.school-for-champions.com/science/static_detection.htm
  • Properties of Charge Add electrons to each of these systems:Charge is conserved: + + + +Charge cannot be created or destroyed. + + +It can only be transferred (by charge carriers*). + + + neutralCharge is quantized: + + + +Charge is found in a smallest “package size” + + +called the elementary charge, e (charge on one + + +proton or electron) measured in Coulombs (C). strong negative charge*electrons + + + + + + + + + + weak positive charge
  • Properties of Charge Add electrons to each of these systems:Charge is conserved: + -+ - +- +Charge cannot be created or destroyed. - + - + - +-It can only be transferred (by charge carriers*). + - + - -+ neutralCharge is quantized: - + - + -+ -+ -Charge is found in a smallest “package size” - - - - +- - + + -called the elementary charge, e (charge on one + - -- -- - + + -proton or electron) measured in Coulombs (C). strong negative charge*electrons + - + +- + Remember: electrons can be added or removed, but -+- + + - protons stay where they are. + +- - + weak positive charge
  • Methods of generating a static charge Only electrons move! Friction Transfer of electrons from one material to a different one through friction. Electrons are ‘peeled’ off one by the other. The triboelectric (or electrostatic) series tells us which materials have a greater tendency to hold on to their electrons and which have a greater tendency to lose their electrons. http://phet.colorado.edu/en/simulation/balloons electron losers electron holders + -
  • Triboelectric series electron losers electron holders + - What happens when…? 1. Aluminium is rubbed against human hair? 2. Fur is rubbed against styrofoam? 3. Teflon is rubbed against styrofoam? 4. Dry hands are rubbed against polyethylene? Where do leather, nylon, polyester and hard rubber fit on the series? Find out more http://regentsprep.org/Regents/physics/phys03/atribo/default.htm
  • Triboelectric series electron losers electron holders + - What happens when…? 1. Aluminium is rubbed against human hair? 2. Fur is rubbed against styrofoam? 3. Teflon is rubbed against styrofoam? 4. Dry hands are rubbed against polyethylene? Where do leather, nylon, polyester and hard rubber fit on the series? Find out more http://regentsprep.org/Regents/physics/phys03/atribo/default.htm
  • Methods of generating a static charge Only electrons move! +- - - - - - - -+ +- - + strong negative charge neutral Conductiona charged material Transfer of electrons from to another material through contact.
  • Methods of generating a static charge Only electrons move! +- - - - - - - -+ +- - + electrons move until they are balanced in both objects Conduction Transfer of electrons from a charged material to another material through contact. Conductors are materials which allow Insulators are materials which do not electrons to flow freely through them. allow electrons to flow freely. examples: examples:
  • Methods of generating a static charge Only electrons move! +- - - - - + +--- -- + negative charge negative charge Conduction Transfer of electrons from a charged material to another material through contact. What would happen if a strong positive charge made contact with a neutral object?
  • Methods of generating a static charge neutral - + -+ +- - - - - - - -+ strong negative charge +- +- insulator Inductionbetween two materials Does not use contact but does require one to be grounded.
  • Methods of generating a static charge + + -- separation of +- - - - - - - -+ charge: electrons strong negative charge + + -- are repelled insulator Induction Does not use contact between two materials but does require one to be grounded.
  • Methods of generating a static charge + + electrons are +- - - - - - - -+ conducted into the strong negative charge + + ground insulator The ground is then disconnected Induction Does not use contact between two materials but does require one to be grounded. The Earth is so big it is always considered neutral
  • Methods of generating a static charge + + object is left +- - - - - - - -+ positively charged strong negative charge + + insulator Induction Does not use contact between two materials but does require one to be grounded.
  • Methods of generating a static charge Only electrons move! Charge is conserved! Friction Transfer of electrons from one material to a The triboelectric (or electrostatic) series tells us different one through friction. Electrons which materials have a greater tendency to hold are ‘peeled’ off one by the other. on to their electrons and which have a greater tendency to lose their electrons. Conductiona charged material Transfer of electrons from Contact is needed. Electrons flow more freely through good conductors. There is net flow until there is balance of charge between the to another material through contact. two objects. Inductionbetween two materials Does not use contact Separation of charge occurs as elecrons can move but protons cannot. By cutting the but does require one to be grounded. ground, the induced object remains charged.
  • Properties of electrostatic charge ‘Like’ charges repel. ‘Opposite’ charges attract. Only electrons have the freedom to move through a material. Observe and explain: Wool is used to charge an acrylic rod. It is brought near the neutral pithball, attracting it. It touches the pithball, after which it is repelled. Why does this happen? Which force is stronger – the electromagnetic force or gravity? Explain your reasoning. Image: pithball electroscope from http://en.wikipedia.org/wiki/Electroscope
  • Build your own simple electroscope What materials do you need? Test it and get some photos - in the resting state - when approached by a negatively charged object - when approached by a positively charged object Image: simple electroscope from http://en.wikipedia.org/wiki/Electrometer
  • How does the electroscope work? Negatively charged rod + Induced charge separation + - electrons in the rod repel electrons + - in the electroscope electrons are forced into the leaves - - negatively charged leaves repel - - - Negatively charged leaves Image: simple electroscope from http://en.wikipedia.org/wiki/Electrometer
  • How does the electroscope work? Positively charged rod - -- Induced charge separation - - protons in the rod attract electrons in the electroscope - electrons move away from the leaves - positively charged leaves repel + Positively charged leaves + + Image: simple electroscope from http://en.wikipedia.org/wiki/Electrometer
  • Can we measure charge?How could we use an electroscope tomeasure the charge of an object? Image: needle electroscope from http://www.farraguttn.com/science/milligan/APPhys/AElctLab.htm
  • Properties of ChargeCharge is conserved:Charge cannot be created or destroyed.It can only be transferred (by charge carriers*).Charge is quantized:Charge is found in a smallest “package size”called the elementary charge, e (charge on oneproton or electron) measured in Coulombs (C).*electrons Image: needle electroscope from http://www.farraguttn.com/science/milligan/APPhys/AElctLab.htm
  • Electrostatic discharges Explain what is happening in these animations. They are different! http://phet.colorado.edu/en/simulation/travoltage http://regentsprep.org/Regents/physics/phys03/atribo/ What environmental conditions favour static shocks? What can you do to reduce the chance of getting a static shock? Image: needle electroscope from http://www.farraguttn.com/science/milligan/APPhys/AElctLab.htm
  • What causes lightning? http://www.youtube.com/watch?v=H_MG__53wsM Image: ¡Rayos! 27 http://www.flickr.com/photos/11039104@N08/2926143475
  • Make some lightning!Try this in a darker part of the class. Be careful.Use the styrofoam and rabbit fur to generate a static charge.Touch the aluminium disc against the styrofoam.Touch your finger against the disc.What happens when the disc approachesthe electroscope? Why?
  • Little house on the prairie This little house is exposed and prone to being struck by lightning. Explain why – and then explain why the owners should install a lightning rod. Image: little house from http://www.supercoloring.com/pages/little-house-in-ukraine/
  • Be safe at the petrol pump!Watch this video and suggest what could have happened.What types of electrostatic transfers took place? http://www.youtube.com/watch?v=tuZxFL9cGkI
  • What do the Mythbusters say about it?http://www.youtube.com/watch?v=uw6-PhvcS3M
  • Be safe at the petrol pump! This guy is trying to bring leather pants back into fashion. He also loves hairspray and his boots with thick rubber soles. What advice would you give him when he goes to the gas station in his super-cool Lada Samara with polyester seating?
  • Are cell phones dangerous at petrol pumps?http://www.youtube.com/watch?v=QkJdaU92Ln8
  • Are cell phones dangerous at petrol pumps? Don’t risk it – follow the rules!http://www.youtube.com/watch?v=QkJdaU92Ln8
  • Is this plausible? Could you really cook an egg with one finger? http://www.youtube.com/watch?v=QT789U0Ld60
  • Is this plausible? Could you really power a house with static electricity? http://www.youtube.com/watch?v=scUosAkxlvo
  • Current Electricity Construct and explain. http://phet.colorado.edu/en/simulation/circuit- http://www.slideshare.net/gurustip/current- construction-kit-ac-virtual-lab electricity-11092690 Build circuits using this simulation and try to replicate them with the materials in the lab. Use the battery (DC) only. Download and edit the Current Electricity presentation above. Complete the questions in the presentation and submit.
  • Why does the bulb glow? This cross-section models the flow of electrons through a lamp. The large dots represent atoms in the filament. Open the animation and find out: 1. What do the red dots and the small yellow dots represent? 1. As the current increases, what happens to: a. The flow of electrons? b. The rate of collisions with the filament atoms? c. The energy carried by the flowing electrons? The resistance of the filament remains constant. If it were replaced with a bulb of greater resistance, would the bulb glow brighter, dimmer or stay the same? Explain why. Resistance at the Molecular Level: http://micro.magnet.fsu.edu/electromag /java/filamentresistance/
  • Note in this example that the large yellow dots remain constant.Resistance These are atoms in the filament which impede the flow of the electrons – they cause resistance to the current. Some materials have greater electrical resistance than others. Wires have resistance, though this is not apparent in the simulations we have used. Resistance can be increased by: • Heating the wire or resistor (atoms vibrate more and so are more likely to impede the flow of electrons) • Making the wire thinner • Making the wire longer Increasing the resistance of a bulb does not make it brighter.Resistance at the Molecular Level:http://micro.magnet.fsu.edu/electromag Remember that electrons are flowing round the whole/java/filamentresistance/ circuit. An increase in resistance slows the flow of electrons and the bulb is dimmer. Energy-efficient bulbs have lower resistance than other bulbs due to the materials they are made from.
  • Arrange this equation based on your own observations. A = Ω VRIV potential difference resistance current 40
  • Arrange this equation based on your own observations. V potential difference I= RA current V Ω resistance 41
  • Electrical Misconceptions A used battery weighs less than a new battery because it has used up all its charge. . A used battery weighs less than a new battery because it has lost its electrons. . A used battery does not weigh less than a ‘full’ battery. Image from http://www.edupics.com/image-battery-i10096.html
  • Electrical Misconceptions The electrons move quickly, but bulb A is closer to the battery, so will light up first.. A B C Clipart people from: http://www.clker.com/search/krug/1
  • Electrical Misconceptions Bulb C is closer to the negative terminal of the battery, so it will get the electrons first and will glow more brightly. Bulb B will be dimmer and A will be dimmest. A B C Clipart people from: http://www.clker.com/search/krug/1
  • Electrical Misconceptions The current that returns to the battery is almost zero because most of the current has been used by the bulbs. Clipart people from: http://www.clker.com/search/krug/1
  • Electrical Misconceptions The bulb has burned out. If I replace it with a bulb of different resistance it will be the same brightness. This is because the battery is the same. Clipart people from: http://www.clker.com/search/krug/1
  • Electrical Misconceptions If I add bulb X to my circuit, it will only affect the brightness of bulb B. A B C X Clipart people from: http://www.clker.com/search/krug/1
  • Electricity & Magnetism – what’s the link? When I bring a disconnected wire close to the compass… When I bring a connected wire close to the compass… Clipart people from: http://www.clker.com/search/krug/1
  • Electricity & Magnetism – what’s the link? If the current affects the compass, do magnets affect current? Have a go at this PhET Lab to explain the relationship between magnetism and current. How do we generate the electricity we use? PhET Lab: Faraday’s Electromagnetic Experiment http://phet.colorado.edu/en/simulation/faraday Clipart people from: http://www.clker.com/search/krug/1
  • How is electrical current generated? What happens when you rotate the handle with constant motion and speed up or slow down? Why? What happens when you move the handle back and forth? Why? What feels different when you connect and disconnect the bulb? Why? Connect up some series circuits like you have createdWhat’s happening in here? in the ‘Current Electricity’ tasks. Do the same rules appear to be true? What happens if you connect a second hand-generator to the circuit and let it go? (Don’t grab the handles of both at the same time). Hand generator from http://www.usi.edu/stem/Equipment_page.asp
  • 51
  • Renewable vs Non-renewable energy Explain the problems we face in the world regarding energy use. With a partner and a GoogleDoc or whiteboard find out about two forms of generating electricity: one based on combustion of fossil fuels and one renewable. Thinking from a One World perspective, compare the two methods. • What are the pros and cons of each? • How do they work? • To what extent is the renewable source a viable alternative to the fossil- fuel based source? What directions could Japan take to ensure a sustainable source of electricity? 52
  • What do you think? Ideas based on Concept Cartoons: http://www.conceptcartoons.comClipart people from: http://www.clker.com/search/krug/1
  • Some basic circuit symbolsYou can use these to build the circuits on the next slides. wire cell battery junction + - + - cathode anode electron flow bulb/ lamp resistor conventional current What do these two components measure? switch V A voltmeter ammeter
  • For more resources. Please consider a donation to charity via Biology4Good. Click here for more information about Biology4Good charity donations.This is a Creative Commons presentation. It may be linked and embedded but not sold or re-hosted.