1. Do Now #33…  Explain the right hand rule and what is meant by it.

2. Objective…  I will be able to describe how electricity is made in a magnetic field.

3. Electricity by definition is electric current that is used as a power source! This electric current is generated in a power plant, and then sent out over a power grid to your homes, and ultimately to your power outlets.

4. The movement of charges such as electrons is called current, and this electrical current is what powers household appliances. Electric Current = Charge Passing Through A Given Area ------------------------------- Time

5. An easier way to think of electric current is to picture cars going through a Turnpike or Parkway Toll. The cars could represent electrons or charge, and the toll booth could represent the cross sectional area of the wire at a certain point. If you counted the number of cars or electrons, that passed through the toll booth or a certain cross sectional area of the wire, and divided that number by the time it took for those cars or charges to pass, you would get the current!

6. Electric current generation - whether from fossil fuels, nuclear, renewable fuels, or other sources is usually based on the:

7. In September of 1831, Michael Faraday made the discovery of Electromagnetic Induction. Faraday attached two wires to a disc and rotated the disc between the opposing poles of a horseshoe magnet creating an electric current.

8. An electric current is not generated unless the magnetic field is moving relative to the copper wire, or the copper wire is moving relative to the magnetic field. If you place a magnet and a conductor (copper wire), in a room together there will be no electric current generated. This is because motion, from our equation for electricity, is missing!

9. So simple electric generators found in power plants contain, magnets and copper wire that when put into motion relative to one another create the electric current that is sent out to homes. The major problem in electricity generation Is where does the Motion come from that keeps the copper wire and magnets moving relative to one another. In this case, wind power applies a force to the blades that turns them. The spinning blades, spin an armature that turns the copper wire relative to the magnetic field. As long as the blades spin, electricity will be generated!

10. - AC of 60 Hz produced by generator - Resistance losses are smallest at high voltages and low currents

11. At home, electric current that was generated by generators in the power plant is used to power electric appliances. The electric current, running through the copper wire causes the armature to spin which is how most motors generate motion.

12. Where does the motion needed to keep the copper wire moving relative to the magnetic field come from? Wind generated Kilronan Wind Farm In Ireland -attains between 50 – 70% efficiency - one windmill’s average energy output ranges from 11.4 W/m^2 – 57 W/m^2 depending on how windy -wind farms tend to generate between 50 and 600 Kw - California currently produces ¾ of all the wind generated electricity in the world. -North Dakota with 20 times the wind potential of California has not erected a single wind turbine

13. Wind power classes 3 (300-400 W/m2) to 7 (800-2000 W/m2) are suitable for wind power development

14. -Wind variability must be overcome by system design - Basic energy Storage - Differences in pressure gradients around wind turbines affect birds -Noise from the turbines affects people and animals -Eyesore, the appearance of mile after mile of wind machines with transmission lines is of concern to the public

15. Water generated - Hydroelectric Shasta Dam In California -Conversion from potential energy of water to electric energy is at 80 – 90% efficiency -Hydroelectric projects in the United States have rated capacities from 950 – 6480 MW -The use of Water Power is much greater in some other countries. Norway obtains 99% of its electricity from water power. Nepal, Brazil, and New Zealand are close seconds.

17. - Hydroelectricity has dropped from producing 30 % to 10% of US electricity - Large fluctuations in output are mainly due to variable rainfall totals

18. -About 50% of the United States potential for hydroelectric energy has been tapped. However, further advances are unlikely. -The Wild and Scenic River Act and the Endangered Species Act have inhibited development of some sites -Silt collection in hydroelectric Dam storage volumes over time causes maintenance issues, as well as environmental concerns -The loss of free flowing streams and land due to flooding behind the dam disturbs the life of species: eg – Salmon - Possibility of dam failure

19. Fossil Fuels – Oil Refinery Pasadena - Texas Standard Large Power Plants Provide 1 Giga-watt of electric power and releases 2 Giga-watts of thermal power as waste heat. An efficiency averaging around 30%. -9000 tons of coal a day -40,000 barrels a day or one tanker a week of oil -generates about 5.3 x 10^9 kwh/year -powers a city of a million people

21. Oil Drilling Platform Cook Inlet, Alaska -total world production in 1996 of petroleum is 62,239e3 barrels / day -an average well in the US produces only 11 barrels / day -In Saudi Arabia an average well produces 9600 barrels /day

24. Nuclear Power Diablo Canyon - California -Plant electrical output 1220 MW -Plant efficiency 34% -There are 109 power reactors in the United States -Produce 22% of nation’s electricity - In France 79% of electricity comes from nuclear reactors

26. -In normal operations a nuclear reactor produces some environmental emissions. E.g.: escape of radioactive fission products through cracks and diffusion, radioactive H3 in small amounts in discharged water -Core meltdown are possible, but unlikely due to negative feedback and shutdown systems -Even after shutdown there is 7% of normal power generation still in the reactor fuel rods. This may be sufficient enough to melt core and destroy the reactor, if cooling water is not supplied -A study entitled “Severe Accident Risks: An Assessment for Five US Nuclear Power Plants” conducted by NRC in 1990, shows that for all the 109 reactors now operating in the United States over a 30 year lifetime there is about a 1% chance of a large release due to internal events.

27. -Solar Power – uses the sun energy to either boil water or directly converts solar energy to electrical energy -Ocean Thermal Energy Conversion – uses temperature differences between different depths of ocean water to drive a heat engine. Working fluid is ammonia which is gas at room temperature. -Biomass Energy: Municipal Solid Waste – burning wastes to drive heat engines -Geothermal Energy – based on naturally occurring heat in the Earth in the Earth due to radioactive decay -Tidal Energy – uses the gravitational pull of the moon on our oceans to drive turbines

28. Proportion of World’s energy consumption - 1997 Proportion of the world’s Electricity generation - 1997

31. Do Now #34…  Explain what the formulat V=IR stands for. If you don’t know be creative.

32. Objective…  I will be able to decribe the equation V=IR and explain what each component means and what happens when each variable it changed.  I will also build a simple electrial magnet based upon the right hand rule and V=IR equation.

33. Do Now #35…  How much resistance in ohms does a battery have that produces 12 Volts at 120 amperes (amps)?

34. Objective….  I will be able to calculate the different

35. What is electricity? The collection or flow of electrons in the form of an electric charge

36. What is static electricity? When two objects rub against each other electrons transfer and build up on an object causing it to have a different charge from its surroundings. Like the shoes rubbing against the carpet. Electrons are transferred from the carpet to the shoes.

37. As electrons collect on an object, it becomes negatively charged. As electrons leave an object it attains a positive charges. Charges interact with each other: Often when you remove clothes from the clothes dryer, they seem to stick together. This is because some of the clothes have gained electrons by rubbing against other clothes. The clothes losing electrons become positive. The negative clothes are attracted to the positive clothes. Have you ever rubbed a balloon on your hair and stuck it on a wall? How do you think this works?

39. The van de Graaf generator (large silver ball) deposits electrons on the ball. When a person places their hand on the ball and the machine is turned on, electrons are transferred to and collected on the person touching the silver ball. Why do you think this machine affects the hair of the children in the picture?

40. What causes you to be shocked when you rub your feet across carpet? An electrical discharge is the passing of an electric current through the air from a negatively charged object to a positively charge object. This is what causes lightning !

41. Check out these static electricity video clips Static electricity at a gas station Van de Graaf Generator’s effect on human hairVan de Graaf Generator’s effect on human hair Static on Baby’s hairStatic on Baby’s hair Kid gets static going down a slide “Cat abuse” by static electricity“Cat abuse” by static electricity What is a conductor and insulator? A conductor is a material which allows an electric current to pass. Metals are good conductors of electricity. An insulator is a material which does not allow an electric current to pass. Nonmetals are good conductors of electricity. Plastic, glass, wood, and rubber are good insulators

42. How are static charges detected?

43. What is the difference between static electricity and current electricity ? Static electricity is stationary or collects on the surface of an object, whereas current electricity is flowing very rapidly through a conductor. The flow of electricity in current electricity has electrical pressure or voltage. Electric charges flow from an area of high voltage to an area of low voltage. Water pressure and voltage behave in similar ways.

45. The pressure of the water flowing through the pipes on the last slide compare to the voltage (electric potential) flowing through the wires of the circuit. The unit used to measure voltage is volts (V). The flow of charges in a circuit is called current. Current (I) is measured in Amperes (A).

46. What are batteries ? Batteries are composed of a chemical substance which can generate voltage which can be used in a circuit. There are two kinds of batteries: dry cell and wet cell batteries. Below is an example of a dry cell. The zinc container of the dry cell contains a moist chemical paste surrounding a carbon rod suspended in the middle.

47. Wet cell batteries are most commonly associated with automobile batteries. A wet cell contains two connected plates made of different metals or metal compounds in a conducting solution. Most car batteries have a series of six cells, each containing lead and lead oxide in a sulfuric acid solution.

48. What is electrical resistance ? Resistance (R)is the opposition to the flow of an electric current, causing the electrical energy to be converted to thermal energy or light. The metal which makes up a light bulb filament or stovetop eye has a high electrical resistance. This causes light and heat to be given off.

49. ohm (Ω). The unit for measuring resistance is the ohm (Ω).

50. Electrical Calculations – What is Ohm’s Law? I = 3 V 2 Ω I = 1.5 amps

51. What are electric circuits ? Circuits typically contain a voltage source, a wire conductor, and one or more devices which use the electrical energy. What is a series circuit? A series circuit is one which provides a single pathway for the current to flow. If the circuit breaks, all devices using the circuit will fail.

52. What is a parallel circuit? A parallel circuit has multiple pathways for the current to flow. If the circuit is broken the current may pass through other pathways and other devices will continue to work.

53. What is the difference between an open circuit and a closed circuit ? A closed circuit is one in which the pathway of the electrical current is complete and unbroken. An open circuit is one in which the pathway of the electrical current is broken. A switch is a device in the circuit in which the circuit can be closed (turned on) or open (turned off).

54. How is household wiring arranged? Most household wiring is logically designed with a combination of parallel circuits. Electrical energy enters the home usually at a breaker box or fuse box and distributes the electricity through multiple circuits. A breaker box or fuse box is a safety feature which will open

55. How is Electrical Power calculated? Electrical Power is the product of the current (I) and the voltage (v) The unit for electrical power is the same as that for mechanical power in the previous module – the watt (W) Example Problem: How much power is used in a circuit which is 110 volts and has a current of 1.36 amps? P = I V Power = (1.36 amps) (110 V) = 150 W

56. How is electrical energy determined? Electrical energy is a measure of the amount of power used and the time of use. Electrical energy is the product of the power and the time. Example problem: E = P X time P = I V P = (2A) (120 V) = 240 W E = (240 W) (4 h) = 960Wh = 0.96 kWh

57. What is magnetism ? Magnetism is the properties and interactions of magnets The earliest magnets were found naturally in the mineral magnetite which is abundant the rock-type lodestone. These magnets were used by the ancient peoples as compasses to guide sailing vessels. Magnets produce magnetic forces and have magnetic field lines

58. Magnets have two ends or poles, called north and south poles. At the poles of a magnet, the magnetic field lines are closer together. Unlike poles of magnets attract each other and like poles of magnets repel.

59. The earth is like a giant magnet! The nickel iron core of the earth gives the earth a magnetic field much like a bar magnet.

60. What are magnetic domains? Magnetic substances like iron, cobalt, and nickel are composed of small areas where the groups of atoms are aligned like the poles of a magnet. These regions are called domains. All of the domains of a magnetic substance tend to align themselves in the same direction when placed in a magnetic field. These domains are typically composed of billions of atoms.

61. Electricity and Magnetism – how are they related? When an electric current passes through a wire a magnetic field is formed.

62. What is an electromagnet ? When an electric current is passed through a coil of wire wrapped around a metal core, a very strong magnetic field is produced. This is called an electromagnet.

63. What is a galvanometer ? A galvanometer is an electromagnet that interacts with a permanent magnet. The stronger the electric current passing through the electromagnet, the more is interacts with the permanent magnet. The greater the current passing through the wires, the stronger the galvanometer interacts with the permanent magnet. Galvanometers are used as gauges in cars and many other applications.

64. What are electric motors? An electric motor is a device which changes electrical energy into mechanical energy.

65. Go to the next slide  How does an electric motor work?

66. Simple as that!!

67. We have seen how electricity can produce a magnetic field, but a magnetic field can also produce electricity! How? What is electromagnetic induction? Moving a loop of wire through a magnetic field produces an electric current. This is electromagnetic induction. A generator is used to convert mechanical energy into electrical energy by electromagnetic induction. Carefully study the next diagrams:

69. Direct current versus alternating current – AC vs DC : What’s the difference? Direct current is electrical current which comes from a battery which supplies a constant flow of electricity in one direction. Alternating current is electrical current which comes from a generator. As the electromagnet is rotated in the permanent magnet the direction of the current alternates once for every revolution. Go to this website and click the button for DC then for AC to visually see the difference between the two.this website You can see that the DC source is a battery – current flows in one direction. The AC source is the generator and the current alternates once for each revolution.

70. Electric Current and Resistance Physics Mrs. Coyle

71. Part I  Basic electric circuit and its diagram.  What causes the flow of electrons in a circuit.  Drift velocity.  Voltaic cell.

72. Electric Circuit

73. Diagram of Electric Circuit

74. Remember: Electric Potential Energy- Two Unlike Charges Higher Potential Energy Lower Potential Energy + - To cause movement of a charge, there must be a potential difference.

75. While the switch is open:  Free electrons (conducting electrons) are always moving in random motion.  The random speeds are at an order of 10 6 m/s.  There is no net movement of charge across a cross section of a wire.

76. http://hyperphysics.phy- astr.gsu.edu/HBASE/electric/imgele/micohm.gif What occurs in a wire when the circuit switch is closed?

77.  An electric field is established instantaneously (at almost the speed of light, 3x10 8 m/s).  Free electrons, while still randomly moving, immediately begin drifting due to the electric field, resulting in a net flow of charge.  Average drift velocity is about 0.01cm/s.

78. Closing the switch establishes a potential difference (voltage) and an electric field in the circuit.  Electrons flow in a net direction away from the (-) terminal. High Potential Low Potential

79. Question:  If the drift velocity is about 0.01cm/s, why do the lights turn on instantaneously when the circuit switch is closed?

80. Conventional Current  By tradition, direction in which “positive charges” would flow.  Direction is opposite of electron flow.

81. Question: What is required in order to have an electric current flow in a circuit? Answer: 1. A voltage source. 2. The circuit must be closed.

82. Battery (Chemical Cell):  A device that converts chemical energy to electricity.  A battery provides a potential energy difference (voltage source).

83. Voltaic Cell  Alessandro Volta (1800’s)  Battery

85. Cu and Zinc Electrodes. Why?

86. Question: Why is the bird on the wire safe?

87. Question: Why do electricians work with one hand behind their back?

88. Question: Why is the ground prong longer than the other two in a plug?

89. Example: Third rail of subway http://static.howstuffworks.com/gif/sub way-track.gif

90. Part II  Electric Current  Ammeter  Resistance  Resistor

91. Electric Current:  The flow of electric charges.

92. Electric Current, I I = q t  Rate  Unit: Coulomb / sec = Ampere (A)  Andre Ampere (1775-1836)

93. http://media-2.web.britannica.com/eb-media/36/236-004-D4AA985F.gif Conventional current has the direction that the (+) charges would have in the circuit.

94.  Direct Current  DC  Provided by batteries  Alternating Current  AC  Provided by power companies

95. Ammeter  Measures electric current.  Must be placed in series.

96. Example:  What charge flows through a cross sectional area of a wire in 10min, if the ammeter measures a current of 5mA?  Answer: 3C

97. Resistance  Resistance of an object to the flow of electrical current.  R= V / I  Resistance equals the ratio of voltage to current.  Unit: Ohm (Ω)

98. Ohm’s Law (Georg Ohm, 1787-1854) V = IR  The voltage, V, across a resistor is proportional to the current, I, that flows through it.  In general, resistance does not depend on the voltage.

99. Ohmic Resistor  A device that obeys Ohm’s Law, who’s resistance does not depend on the voltage.

100. Resistor  An object that has a given resistance.

101. A Battery Provides Energy Electric Circuit  The battery “pumps” positive charges from low (-) to high (+) potential.

102. Resistors use up Energy Electric Circuit  A resistor uses up energy.  When the current goes through the resistor it goes to a lower potential.

103. Question: Electric Circuit  Which point has a lower potential, A or B?

104. Example:  Calculate the current through a 3 Ω resistor when a voltage of 12V is applied across it.  Answer: 4 A

105. Example:  A 6 Ω resistor has a power source of 20V across it. What will happen to the resistance if the voltage doubles?

106. Part III  Factors that affect resistance.  Potentiometer  Voltmeter

107. Resistance  Depends on type of material, size and shape, temperature. R=ρ L A L: length of the wire A: cross-sectional area ρ: resistivity (inherent to material)

108. Example:  What happens to the resistance when the length is doubled and the area is quadrupled?  Answer: It changes by 1/2

109. Temperature Dependence of Resistance  For metals: as temperature increases the resistance increases.At very low temperatures resistance can become zero: superconductivity.  For semiconductors: the opposite occurs.

110. Potentiometer  A variable resistance.  Used for dimmers, fan speed controls, etc.

111. Potentiometer Symbol

112. Voltmeter  Measures the voltage between two points in an electric circuit.  Must be connected in parallel.

113. A voltmeter is connected in parallel.

114. Ammeter  Measures electric current.  Must be placed in series.

115. Ohm's law magic triangle

116. Ohms law, defines the relationship between voltage, current and resistance. These basic electrical units apply to direct current, or alternating current. Ohm’s Law is the foundation of electronics and electricity. This formula is used extensively by electricians. Without a thorough understanding of “Ohm’s Law” an electrician can not design or troubleshoot even the simplest of electronic or electrical circuits. Ohm established in the late 1820’s that if a voltage was applied to a resistance then “current would flow and then power would be consumed”.

117. Voltage measured in volts, symbolized by the letters "E" or "V". Current measured in amps, symbolized by the letter "I". Resistance measured in ohms, symbolized by the letter "R".

119. If you know E and I, and wish to determine R, just eliminate R from the picture and see what's left:

120. If you know E and R, and wish to determine I, eliminate I and see what's left:

121. if you know I and R, and wish to determine E, eliminate E and see what's left:

122. Let's see how these equations might work to help us analyze simple circuits: If we know the values of any two of the three quantities (voltage, current, and resistance) in this circuit, we can use Ohm's Law to determine the third.

123. calculate the amount of current (I) calculate the amount of current (I) in a circuit, given values of voltage (E) and resistance (R):

124. calculate the amount of resistance (R) in a circuit, given values of voltage (E) and current (I):

125. calculate the amount of voltage supplied by a battery, given values of current (I) and resistance (R):

126. Ohm’s Law power consumption through a resistance Some practical every day examples of this basic rule are: base board heaters, electric frying pans, toasters and electric light bulbs. The heater consumes power producing heat for warmth, the frying pan consumes power producing heat for general cooking, the toaster consumes power producing heat for cooking toast, and the electric light bulb consumes power producing heat and more important light. A further example is an electric hot water system. All are examples of Ohm’s Law.

132. The force or pressure behind electricity

137. milliamp or just mA

138. As a milliampere (milliamp or just mA) is 1/1000th of an ampere, we can convert mA to Amps by just dividing by 1000. Another way is to take the current in mA and move the decimal to the left three places to accomplish the division by 1000. Here's the scoop: 275 mA / 1000 = 0.275 Amps Note that the decimal in 275 is to the right of the 5, and it's written as 275.0 (with a 0 added to show where the decimal is). Moving the decimal to the left three places gets up to.275 Amps, but we usually hang a 0 in front of the decimal. To convert Amps to milliAmps, just multiply by 1000 or move the decimal to the right three places. Just the opposite of what we did here to convert the other way.