Electricity

1. Electricity Principles and Technology

2. Have you ever wondered??? • How does electricity get to our wall sockets • How does it know exactly how much we need? • Exactly what happens inside a battery? • How does solar energy power our space station or simply our calculators? • Is there an environmental impact from the way we produce and use electricity? • How can we use electricity best for us and our environment?

3. Topic 1 - Electric Charges • What we call electricity is the energy of moving electric charges or electrons. • When charges move they produce energy • Moving charges can be seen when • Lightening bolts • Sparks are created from combing your hair • Electrical currents in light bulbs

4. Types of Electric charges • Neutral – Object has # positive = # negative. + + + - - - • Negative – Object has more negative than positive charges. + + - - - - • Positive – Object has more positive than negative charges. + + + + - -

5. Static vs Current Electricity • Static electricity is a charge produced by touching or rubbing objects together. The object then has an unbalanced charge that is static, not moving. • When you touch an object that has static electricity it can use you to become balanced or neutral. As a result you may feel a shock. This is called DISCHARGING • Current Electricity is when electricity is flowing in a path through conductive material. It is not building up or static in an object.

6. Producing a Charged object • Have you ever rubbed a balloon on your hair?? If so, you were producing charged object or static electricity • Combinations of materials become charged when they are rubbed pass each other. • Electrons move from one object to the other Bad hair day!

7. Movement of electrons

8. Laws of Charges • Like charges repel • Unlike charges attract • Charged objects attract uncharged objects

9. Conductors Conductor – materials that allow a charge to move freely; most metals are conductors Different materials vary in their ability to conduct electricity. They may be may be good, fair or poor(insulators) List several of each below:

10. Insulators • Insulator – any material in which the charge stays in one spot where the object is rubbed. Ex: balloon. Most nonmetals are insulators Glass or plastic insulators high up on power poles keep electricity from traveling down the pole to the ground. Insulators keep electricity from leaving power lines.

11. Superconductors • Superconductors – materials that offer little resistance to the flow of charges. Made of metal alloys and ceramics • Certain material become superconductors at extremely low temperatures -137.5oC to -273.15oC. Power lines. A significant amount of electrical energy is wasted as heat when electricity is transmitted down cables made of traditional metal conductors. Superconductors, however, can conduct electricity with zero electrical resistance and would therefore be vastly more efficient.

12. Neutralizing Unbalanced Charges • Static Cling on your clothes?? • The rebalancing of unbalanced charges results in a electric discharge – may cause the release of small spark. • Electrons transfer to balance the + and – charges in the material. Bounce sheets or static guards work by preventing the buildup of charges or by dissipating charges that are already present.

13. Grounding • Grounding is connecting an object to earth with a conducting wire. • Earth is so large it easily supplies enough electrons to neutralize charges on objects by receiving or supplying electrons. Gasoline trucks and airplanes pick up charges traveling due to rubbing with the air and dust particles. Before gassing up they must be grounded with cables to prevent sparking that could cause gasoline fumes to explode.

14. Homework • Textbook p.271 Q#1-6

15. Van de Graaff generator • In your own words explain how the VDG generator works. In your explanation use the terms: static charge, unbalanced charge, conductor, laws of charges, grounding. • HAND IN YOUR EXPLANATION.

16. Topic 2 Electricity Within a Circuit • A continuous pathway for charges to move is a circuit • How do circuits work? • What are all those components?

17. What are the basic components of a circuit? • There are 4 basic components • 1. Source – source of electric energy ex: battery • 2. Conductor – The wire through which current flows

18. What are the basic components of a circuit? • 3. Control – switch or device that can turn the circuit or devices along it on or off. • Ex: Light switch in your house

19. What are the basic components of a circuit? • 4. Load/resistors – Items along the circuit that convert electricity (moving charges) into other energy • Ex: light bulbs, motors, heaters, speakers

20. Drawing Circuits • Electricians and engineers draw circuit diagrams to help them design actual circuits • First we need to know the symbols used: There are 7 main ones: The 7th symbol - lamp

21. Drawing Circuits • Drawing requires you to follow these 5 criteria: • Use a pencil, ruler, graph or unlined paper • Place all 4 components in a rectangular or square arrangement • Make conductors (wires) straight lines with right angles • Conductors- straight lines do not cross • Draw neatly, make symbols a consistent size.

22. Electric Circuits

23. Drawing circuits • Example – see figure 4.9 on page 273 in your text. • What is missing from the below circuit

24. Practice making and drawing circuits • See page 272 in text • Hand in sketches, and questions 1,2,3,4 and the extension activity

25. Measuring Electric Current • Think of a river with flowing water. • You could describe the current as the amount of water flowing past a certain point every minute. • Electric current (I) is the amount of charge that passes a certain point in the conducting wire. • This amount is measured in Amperes (A) 1 A = 1 coulomb = energy in 6.25 x 1018

26. Measuring Electric Current • Galvanometer – measure small or weak electric current • Ammeter – measure larger or strong currents

27. Voltage • Potential difference is the same as Voltage • The difference in electric energy per unit (or amount) of charge between one point In a circuit and another point in the circuit. • This difference is called potential difference or Voltage • The standard unit is a volt (V) • Volts are measured by a Voltmeter.

28. Rivers of Electricity Electric circuits are often compared to water systems. (see diagram in text pg 278) Do question 1 page 278

29. Current and Voltage Lab • See page 276 of text book • Part A • Purpose • Hypothesis • Observations/results – table p. 276 • Questions p. 276 1,2,3,4 • Part B • Purpose • Hypothesis • Observations/results: - table p. 277 • OMIT D(with 3.7V bulb) and E(bulbs unscrewed) • Questions: p.277 1,2,3,4

30. Topic 3 Resisting the Movement of Charge • Resistance is the property of a substance that hinders the motion of electric charge and converts electric energy into other forms of energy. • Ex: Light bulb filament wires – tungsten 400x more resistance than copper wire. Light bulb with tungsten would be much brighter than a light bulb with copper wire. Tungsten

31. Resistance • The negatively charged electrons must force their way through solids overcoming resistance caused by the attraction of positively charged atomic nuclei and the repulsion of other electrons. • A good conductor has low resistance • A poor conductor has high resistance • Do you know a game where the lowest score is better? See text page 279 for diagram

32. Calculating Resistance • Units of resistance is ohms (Ω) • Ohms are measured using a Ohmeter • The following formula (Ohm’s law) is used to calculate resistance: • Current (I) must not be in milliamps if given this way it must be x 1000 to get back to Amperes • Can rearrange formula to find current or voltage Resistance (R) = Voltage (V) Current (I)

33. Calculating Resistance • Example: • What is the resistance of an electric heater, if a current of 12.5A runs through it when it is connected to a 120V wall outlet? • I = 12.5 A • V = 120V • R = V/I • R = 120V / 12.5A = 9.6 Ω • The resistance of an electric heater is 9.6 Ω if the current through it is 12.4A with a 120 V supply.

34. Practice • Do 4 practice problems on page 282 in your text. Record all your workings. • Handout BLM 4.7

35. Voltage, Current, Resistance lab • See page 284 text • Purpose: • Hypothesis: • Observations/results: table on page 285 • Questions: p.285 1,2,3,4,5,6

36. Variable Resistors • Variable resistors do not have a fixed resistance. Their resistance is affected by various factors. Ex: Wire • 1. Length of wire • Longer wires higher resistance • 3x length 3x resistance; 4x length 4x resistance (draw diagram in notes) • 2. Temperature of wire • Higher temperature higher resistance

37. Variable Resistors • 3. Diameter of the wire (x sectional area) • Larger diameter the lower the resistance (draw diagram in notes) • 2x diameter = ½ resistance • 3x diameter = 1/3 resistance • 4x diameter = ¼ resistance • Etc • Common uses are: • Controlling brightness of lights – light dimmers • Controlling the speed of motors • Controlling temperature - thermostats

38. Resistance Road block Lab • See page 280 • Purpose: • Observations/Results: copy and complete the table • Questions: 1,2,3 and extension 1,2

39. Series: Single pathway. Charge (moving electrons) travel through each component Parallel: More than one pathway. Current is divided and travels through each pathway (branch) Two Types of Circuits Homes are wired with parallel circuits to allow for all your appliances to operate independently

40. House Wiring • Parallel circuits are used • Benefit - turning on one appliance does not reduce the energy available for other appliances – the voltage across each load is the same • Problem – turning on many appliances at once increases the current and this increases the temperature of the wires and could start a fire. • Fuses or circuit breakers prevent this from happening.

41. Series and Parallel Circuits lab • See page 287 of text book • Purpose • Part A • Hypothesis • Results • Table for part A on page 27 • Draw your circuit • Conclusion: Questions 1-6 • Part B • Hypothesis • Results • Table for part B on page 27 • Draw your circuit • Conclusion: Questions 1-6

42. Review • Designing Circuits (BLM 4-10) • Handout “check and reflect” questions 1,4,5, 7,11 • Design a circuit for a room that has two lights and two fans that can operate independently but are on the same circuit? [if time]

43. What are the other forms of Energy? What appliances convert one form of energy to another? Topic 4 The Energy ConnectionHow can electricity be converted to other forms of Energy?

44. Forms of Energy • Electric - is the flow of electrons along a circuit. The movement of electrons creates an electric current which generates electricity • Kinetic - is the release of the stored energy to create motion. • Mechanical - refers to an object that is doing work by being in motion. • Chemical - is generated from chemical reactions in which the chemical bonds of a substance are broken and rearranged to form new molecules that can provide energy. • Solar - Is the energy transmitted from the Sun • Nuclear - is generated when parts of the atoms in certain materials split off in a controlled environment.

45. Stove: electric heat Hair dryer: electric  heat Electric Car: electric  mechanical  kinetic Solar Cell: solar  electric Generator: mechanical  electrical Battery: chemical  electrical Examples of Energy transfers • What others can you think of? • Read text pages 293-299 and do questions 1-2 on page 299.

48. Topic 8Electricity and the Environment • There are many ways in which we produce electricity. Some are more harmful to our environment than others. • Thermo-electric generating plants. Some use coal. Coal is made up of carbon but when we mine it is not pure. It is one of the most impure of fuels containing many different substances including sulfur and nitrogen http://www.epa.gov/acidrain/education/site_students/acid_anim.html

49. Controlling air pollution • Scrubbers Spray water Solution through Waste gases. Pollutants react With the chemicals In the water and Are removed

50. Generating Electricity 2. Hydro-electric plants (kinetic to electric) http://ga.water.usgs.gov/edu/hyhowworks.html