1. ELECTRICITY!!

2. Electricity –From the word “Elektron” –Greek for “amber” –Electricity is simply the flow of electrons.

3. “Laws of Attraction” Opposite Charges Attract Like Charges Repel + - ++

4. Question: If you remove the 2 batteries from a working flashlight and reinstall them backward so that they make good contact inside, will the flashlight still work? Question on batteries

5. Observations About Flashlights (and electrical circuits) They turn on and off with a switch More batteries usually means brighter The orientation of multiple batteries matters Flashlights dim as batteries age Observations about flashlights

6. battery, switch, light bulb, wire. For a functioning battery we need:

7. An electrical current (electrons) runs through all the parts of the circuit (close circuit). No current flows when switch is open (open circuit). Electrons carry energy from batteries to the bulb. Short circuit: A path (short cut) in which the light bulb is cut out. In a flashlight we are creating an: Electrical circuit

8. A Battery Battery “pumps” charge from + end to – end –Chemical potential energy is consumed –Electrostatic potential energy is produced Current undergoes a rise in voltage –Alkaline cell: 1.5 volt rise –Lead-acid cell: 2.0 volt rise –Lithium cell: 3.0 volt rise Chain of cells produces larger voltage rise Battery

9. A Light Bulb Structure –Contains a protected tungsten filament –Filament conducts electricity, but poorly Filament barely lets charge flow through it –Electrostatic potential energy (voltage) is consumed –Thermal energy is produced Current undergoes a drop in voltage –Two-cell alkaline flashlight: 3.0 volt drop A Light Bulb

10. Electric CurrentWater Analogy hVhV water flowI Current: number of electrons passing through per second Water analogy: number of water molecules passing through per second Electric CurrentWater Analogy

11. I Electric current --> water

12. What determines the current through the circuit (Load)? Ohm’s Law V = I·Ror I = V/R So, 10V across a 100ohm load = 0.1 Amp Where 1 Amp = 1 coulomb/sec = 6.25 x 10 18 e/sec 1Amp=62,500,000,000,000,000,000 electrons/sec I V R What determines the current through the circuit (Load)?

13. Examples 2.A bulb in a lamp that is connected to a household outlet has a resistance of 100 ohms. What current flows through it? 3.Your skin has a resistance of about 10 6 to 10 4 ohms (dry) and 10 3 ohms (wet). What current runs through you when you stick your finger in an outlet (conduction to ground)? 1.A battery can produce 1.5 V. When connected to a light bulb a current of 2 A (Ampere) runs through the bulb. What is the resistance of the bulb? examples

14. The severity of an electric shock depends on the magnitude of the current, how long it acts and through what part of the body it passes. Can feel ~ 1 mA; pain at a few mA; severe contractions above 10 mA; heart muscle irregularities above 70 mA. Resistance of dry skin ~ 10 4 to 10 6 W; wet skin 10 3 W or less. A person in good contact with ground who touches a 120 V line with wet hands can suffer a current Electric shock

15. Positive Charge Current points in the direction of positive flow Flow is really negative charges (electrons) It’s hard to distinguish between: –negative charge flowing to the right –positive charge flowing to the left We pretend that current is flow of + charges It’s really – charges flowing the other way A word about the sign convention…. Positive Charge

16. Electrical Resistance So, we hook up a wire between the terminals on a battery The question is, how much current flows? We have lots of free electrons able to move in the metal composing the wire So, how much charge moves past any point in the wire per second?

17. Electrical Resistance The amount of current that flows is determined by how much resistance there is to the flow of the charges What makes this resistance? Collisions of the electrons with each other and with the “stationary” atoms of the metal Atoms are actually vibrating in the lattice

18. Electrical Resistance Resistance depends on the structure of the material and the temperature The higher the temperature, the more the atoms vibrate and the more electrons make collisions with the atoms How much current flows was discovered by George Ohm, and we honor him by naming the unit of resistance an ohm

19. Ohm’s Law Ohm’s discovery was that current is proportional to voltage and inversely proportional to resistance

20. Ohm’s Law Three forms are convenient

21. Electric Shock We all know not to stick our finger into a light bulb socket or to drop an electrical appliance into our bath tub What causes the damage to our bodies? It is the amount of current that flows through the body that can cause problems Human skin has resistance ranging from 100 ohms to 500,000 ohms (wet to dry)

22. Electric Shock We can use Ohm’s Law to calculate current based on the size of the applied voltage You can feel 0.001 ampere (1 milliampere) 0.005 amperes hurts 0.010 amperes causes muscle spasms 0.015 amperes loss of muscle control 0.070 amperes disrupts heart rythyms (fatal)

23. Electric Shock There must be a potential difference between one part of your body and another You must become a conductor of electricity OK for birds to sit on a 5000 V transmission line as long as no part of the bird touches something else Squirrels get across the transformers

24. Power Power is energy per unit of time Power is measured in joules/second or watts Batteries are power sources Loads are power consumers

25. Battery Power power produced by the battery Current: units of charge pumped per second Voltage rise: energy given per unit of charge P = V rise ·I current · voltage rise = power produced I V rise

26. Load Power Current is units of charge passed per second Voltage drop: energy taken per unit of charge current · voltage drop = power received P = V drop ·I I V drop

28. Electrostatics the study of electrical charges at rest Electrodynamics the study of electrical charges in motion opposite Two opposite types of charge exist, named positivenegativeBenjamin Franklin positive and negative by Benjamin Franklin.Benjamin FranklinBenjamin Franklin Charge is a property of matter. charges

29. Charged particles exist in atoms. Electrons are responsible for negative charge; protons for positive charge; neutrons have no charge. ONLY ELECTRONS MOVE!!!! Small amounts of ordinary matter contain incredible amounts of subatomic particles!

30. When charged particles near one another, They give rise to two different forces. A force is a push or a pull on an object. Basic Law of Electrostatics Like charges repel; unlike charges attract Link link Electrostatic force

31. An electric field extends outward through space from every charged particle. When a charged particle moves into the electric field of another, it is either pushed or pulled. Field lines point away from positive and toward negative charges. field

32. Static Electricity: The buildup of electric charges on an object. A Neutral object gains an electric charge when it gains or loses electrons. Three Methods of Charging an Object 1.Friction - Rubbing two objects together 2.Conduction-touching two objects together. 3.Induction-rearrangement of charges on the object. static

33. Charging objects by friction. Example: Charging a balloon by rubbing it on your hair and then sticking it to a neutral wall.

34. Conduction-Touching of Objects Certain Materials permit electrical charges to flow freely through them. Conductors: Metals, Earth Semi-Conductors: Silicon, Germanium Non-Conductors: rubber, glass, wood, plastic

35. INDUCTION charging without touching of objects

36. rodelectroscope charging a rod and electroscope positivelynegatively positively and negatively conduction induction by conduction and induction conduction When charging by conduction, touches the rod touches the electroscope. same charge The electroscope gets the same charge as the rod. inductiondoes not When charging by induction, the rod does not touch touch the electroscope. The electroscope gets opposite charge the opposite charge of the rod. electroscope

37. Go herehere, here, and here Go here, here, here, and herehere to view simulations of charging an electroscope. Read more here. here links

38. COULOMB’S LAW The force between two charged objects is directly proportional to the product of their charges and inversely proportional to their separation distance squared. link1link1, link2, link3, link4, link4link2link3link4

39. In equation form: F = F is the force of attraction, measured in NEWTONS, between charges q 1 and q 2 k k is the Universal Electrostatic Constant, equal to 9.00 x 10 9 N m 2 /coul 2 q1q1 q2q2 q 1 and q 2 are the attracting charges, measured in Coulombs d2d2 d is the distance between the charges, and is measured in METERS

40. The SI unit of charge is the Coulomb, named in honor of Charles Augustin CoulombCharles Augustin Coulomb. Charles Augustin Coulomb 1 C = charge on 6.25 x 10 18 electrons (or protons) 1 e - = 1.60 x 10 -19 Coul = elementary charge Electric force is a vector and must be treated as such.

41. Electric Fields An electric field exists in a region if space if a charge placed in that region experiences an electric force. The magnitude of an electric field at any given point is defined to be the ratio of the force on a charge at that point to the amount of charge. E = F/Q Electric field strength has units of Newtons/Coulomb (N/C).

42. Click here to view a simulation here showing the magnitude and direction of the electric force on a test charge when placed near other charges. Click here to view a simulation of a here charged particle moving through a region occupied by other charges.

43. Voltage Sources If we want to move charge from one place to another, we must apply a force to make it move Another way of thinking about this is to say that we must give the charges some potential energy

44. Voltage Sources We can give an object gravitational potential energy by lifting it into the air We have to do work on the object to lift it into the air Doing work uses energy Conservation of Energy

45. Voltage Sources

46. We need an pump that pumps charges! The simplest charge pump is a battery It uses chemical reactions to separate charges and thus create electrical potential energy More convenient to talk about PE/charge or electric potential measured in volts So, a battery is a kind of electric pump

47. Voltage Sources Another kind of source is a generator A generator converts mechanical energy into electrical energy In any case, what we need is a device to separate charges!!!

48. Electric Current The movement of charge is called a current Metals have some electrons that are not needed to bond the atoms together in the solid They are pretty free to just roam about the material and are not associated with any individual metal atom

49. Electric Current Compare to the flow of water in a hose

50. Electric Current We measure the flow of water in gallons/minute We measure the flow of charges in coulombs/sec 1 coulomb/sec = 1 ampere Remember this is 6.25 x 10 18 electrons moving past a point in a wire per second

51. Electric Current In a wire, the electrons actually move quite slowly, less than 0.01 meters/sec However, their electric field moves at the speed of light!!! So, we can send signals down a wire very quickly, because the information moves at the speed of the changing electric field which is at the speed of light

52. Electric Current +- Electron flow

53. Electric Current In the 1700’s people figured out that charges could move They had two choices –Positive charge moves –Negative charge moves They guessed WRONG!!!!! We know electrons move

54. Electric Current Hook up a battery and electrons flow from minus terminal to plus terminal Ancients defined current as positive charge flow Direction of “current” is from plus to minus

55. Electric Potential Difference the change in electric potential energy per unit charge V = W/QV = W/Q The SI unit of electric potential VOLT difference is the VOLT, named in Alessandro Volta Alessandro Volta honor of Alessandro Volta.Alessandro Volta One VOLT is the electric potential difference between two points when one Joule of work is done in moving one Coulomb of charge between the points.

56. the flow of charged particles charged particles; can be positive or negative, but usually negative (electrons) through a conducting metal current

57. electric cell - a device that converts one form of energy to electrical energy Chemical cells convert chemical energy into electrical energy. Chemical cells can be “wet” or “dry”.

58. Solar cells Solar cells convert light energy into electrical energy. generator A generator converts mechanical energy into electrical energy. battery battery - two or more cells connected in series or in parallel

59. Electric current is measured in Amperes, in honor of Andre Marie Ampere Andre Marie AmpereAndre Marie Ampere Andre Marie Ampere. One Ampere is the flow of one Coulomb of charge per second. 1 Amp = 1 Coulomb per second = 1 C/s 1 Amp = 1 Coulomb per second = 1 C/s IQt I = Q/t

60. Ammeter a device that measures current Voltmeter a device that measures electric potential difference

61. power = work/time = (work/charge). (charge/time) = electric potential difference. current P (Watts) = V (Volts). I (Amps)

62. Analogies of simple circuits are these links: Water circuit analogy link link Air flow link link Various link link Teaching with Analogies link1, link2 link1link2link1link2

63. Resistance determines the amount of current flow = the ratio of potential difference to current = the ratio of potential difference to current R= V I The SI unit of resistance is the OhmW Ohm, W, named Georg Simon Ohm Georg Simon Ohm in honor of Georg Simon Ohm.Georg Simon Ohm One Ohm One Ohm of resistance is the resistance one Volt such that one Volt of potential difference one Amp is needed to obtain a current of one Amp.

64. The resistance of a circuit element depends on: the length of the conductor 1. the length of the conductor as length increases, resistance increases proportionally the cross-sectional area of the conductor 2. the cross-sectional area of the conductor as area increases, resistance decreases proportionally the resistivity of the conductor 3. the resistivity of the conductor as resistivity increases, resistance increases proportionally

65. Resistivity The resistivity, r, of a conductor is equal to the resistance of a wire 1 cm long and having a cross-sectional area of 1 cm 2. R R = resistance, measured in Ohms = r r = resistivity, usually in units of W. cm l l = length, measured in cm A A = cross-sectional area, measured in cm 2

66. Ohm’s Law The ratio of potential difference to current is constant. If R = V/I is a constant value for a given resistor, then that resistor is said to obey Ohm’s Law. Click here and here to link to pages describing resistor here color codes.

67. Click here and here to run here simulations of Ohm’s Law. Many circuit elements do not obey Ohm’s Law. Resistors that get hot, like light bulbs and heating elements, do not keep a constant resistance. Resistance generally increases as objects become hotter.

68. Resistor Circuits Series 1. total resistance is the sum of the separate resistors separate resistors R T = R 1 + R 2 + R 3 +... 2. current is the same through each resistor I T = I 1 = I 2 = I 3 =... 3. total potential difference is the sum of each V T = V 1 + V 2 + V 3 +... In other words, in a series circuit, resistance and voltage add, but current stays the same. Resistor circuits

69. R1R1R1R1 R2R2R2R2 R3R3R3R3 E = 12 V RT =RT =RT =RT = VT =VT =VT =VT = IT =IT =IT =IT = R1R1R1R1 R2R2R2R2 R3R3R3R3 V,V PT =PT =PT =PT = R,WI,A P,W 8.0 5.0 2.0

70. R1R1R1R1 R2R2R2R2 R3R3R3R3 E = 12 V R T = 15 Ω V T = 12 V I T = 0.80 A R1R1R1R1 R2R2R2R2 R3R3R3R3 V,V P T = 9.6 W R,WI,A P,W 8.0 5.0 2.0 0.80 6.4 1.6 4.0 5.1 1.3 3.2

71. Parallel 1. reciprocal of the total resistance is the 1. reciprocal of the total resistance is the sum of the reciprocals of the separate sum of the reciprocals of the separate resistors resistors 1/R T = 1/R 1 + 1/R 2 +1/R 3 +... 2. total current is the sum of the current through each resistor through each resistor I T = I 1 + I 2 + I 3 +... 3. potential difference is the same across each resistor each resistor V T = V 1 = V 2 = V 3 =... In other words, in a parallel circuit, resistance adds as reciprocals, voltage stays the same, and current splits. In other words, in a parallel circuit, resistance adds as reciprocals, voltage stays the same, and current splits.

72. E = 12 V RT =RT =RT =RT = VT =VT =VT =VT = IT =IT =IT =IT = R1R1R1R1 R2R2R2R2 R3R3R3R3 R,W V,VI,A PT =PT =PT =PT = R3R3R3R3 R1R1R1R1 R2R2R2R2 P,W 12 8.0 12

73. E = 12 V R T = 3.42 Ω V T = 12 V I T = 3.50 A R1R1R1R1 R2R2R2R2 R3R3R3R3 R,W V,VI,A P T = 42 W R3R3R3R3 R1R1R1R1 R2R2R2R2 P,W 12 8.0 12 1.0 1.5 1.0 12 18

74. Go to link1, link2, link3, link4, link5, and link6 to view link1link2link3link4link5link6link1link2link3link4link5link6 pages and simulations examining Kirchhoff’s Loop and Junction Rules. Kirchhoff’s Rules Loop Rule: The sum of the potential differences around any closed circuit loop is zero. Junction Rule: The sum of the currents into any circuit junction is zero.

75. The site linked herehere allows you here to build and test your own series, parallel, and/or combination circuits. For a complete interactive tutorial on electricity and magnetism, go here. here

76. POWER THE RATE OF DOING WORK OR CONVERTING ENERGY. Power = Work / Time Power = Energy / Time UNIT- WATT = JOULE PER SECOND

77. POWER Watt Demonstration: Lift a 1-N mass a distance of 1 meter, and you have done 1 Joule of Work. Do this once each second, and your power output is 1 Watt.

78. POWER Light bulbs are rated by the power used.

79. POWER Power = Current × Voltage What are the units for Current, Voltage, and Power? Ampere = coulomb / second Volt = joule / coulomb

80. POWER What is a Volt X Ampere ? Volt X Ampere = joule/coulomb X coulomb/second Volt X Ampere = joule/second = watt

81. POWER A PAIR OF LEMON BATTERIES GENERATED ABOUT 0.5 MILLIWATTS AN XMAS BULB REQUIRES ABOUT 0.5 TO 1 WATT

82. POWER ACTIVITY HAND HELD GENERATOR

84. Electromagnetism 21-1 Magnetism from Electricity Electromagnetism – relationship between magnetism and electricity Oersted – (1820) Danish physicist who first discovered that an electric current produces a magnetic field. Example of Oersted’s Discovery

85. Solenoid – long coil of wire with a current passing through wrapped into many loops creating a magnetic field. Acts like a magnet when a current is passing through. Strongest at the ends – like a magnet. Increase the strength of the magnetic field: 1)increasing the amount of coils and/or 2) increasing the amount of current. OR by adding magnetic material between the wires. An electro-magnet – solenoid with magnetic material (iron nail) inside the coils. Greatly increases the strength. Strong temporary magnets

86. Just as an electric current exerts a force on a magnet. A magnetic field exerts a force on an electric current (charged particles) Practical devices: Electric motors – converts electrical energy into mechanical energy. Contains a coil of wire connected to a cylinder (armature). Armature free to spin between the poles of a magnet.

87. Galvanometers – instruments used to detect small currents (coil of wire connected to an electric circuit and a needle) Examples: ammeters and voltmeters

88. 21-2 Electricity from Magnetism Faraday – 1831 Englishman – and Henry an American – first to prove that electricity can be produced from magnetism. Electromagnetic Induction - Faraday noticed that changing the magnetic field produced an electrical current – induced current. Faraday’s experiment Another experiment illustrating electromagnetic induction

89. An electric current will be produced (induced) in a circuit exposed to a changing magnetic field. The direction of the current depends on the direction of the moving magnet.

90. Generators – converts mechanical energy into electrical energy – opposite of a motor (electrical energy into mechanical energy) Consist of loops of wire connected to a rotating rod. AC generator DC generator

91. In large generators turbines provide the mechanical energy to turn the axles. Either moving wind, water or steam turn the turbines. Wind power, hydroelectric power, nuclear power or electricity from burning of fossil fuels - coal and oil.

92. Transformers – devices that increase or decrease the voltage of alternating current. In US 60 hertz Consists of 2 coils wrapped around an iron core. AC current passes through first coil, inducing a current in second wire. Step-up transformers – when primary coil has less loops than second coil. Voltage in second coil greater than first coil – step-up transformer (increases voltage) Step-down transformers – more loops in first coil, less in second – voltage in secondary coil less. Power can be conserved if voltage is stepped up before transmission and stepped down before being used by consumer

94. DC and AC Hook up a battery and we have direct current, i.e. current flows ALWAYS in one direction Modern generators in power plants reverse the polarity of the output terminals 60 times per second This is called alternating current It is what comes out of the wall plug

95. DC and AC