2. Lesson 2

3. A Little History… The science of electricity has its roots in observation, people knew in 600 BC that a rubbed piece of amber will attract a bit of straw This strange effect remained a mystery for over 2000 years.

4. History Study of magnetism goes back to the observation that certain naturally occurring stones attract iron The two sciences were separate until 1820 when Hans Christian Oersted saw the connection between them…an electric current in a wire will affect a compass needle

5. Benjamin Franklin In 1752, Franklin proved that lightning and the spark from amber were one and the same thing. This story is a familiar one, in which Franklin fastened an iron spike to a silken kite, which he flew during a thunderstorm, while holding the end of the kite string by an iron key. When lightening flashed, a tiny spark jumped from the key to his wrist. The experiment proved Franklin's theory, but was extremely dangerous - he could easily have been killed.

6. History In 1786, Luigi Galvani, an Italian professor of medicine, found that when the leg of a dead frog was touched by a metal knife, the leg twitched violently. Galvani thought that the muscles of the frog must contain electricity.

7. History By 1792, another Italian scientist, Alessandro Volta, disagreed: he realized that the main factors in Galvani's discovery were the two different metals - the steel knife and the tin plate - upon which the frog was lying. Volta showed that when moisture comes between two different metals, electricity is created. This led him to invent the first electric battery, the voltaic pile, which he made from thin sheets of copper and zinc separated by moist pasteboard.

8. Research on the Atom Through the 19 th century further discoveries about the elements and the atom continued….See your chemistry notes! Then….

9. Millikan’s Oil Drop Experiment 1909 Purpose: to measure the charge on an electron Principle: a drop is suspended if the electric and gravitational forces are balanced (downward force of weight of the drop = the upward force of the electric field on the drop). Nobel Prize 1923

10. 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 Franklin Benjamin Franklin Charge is a property of matter.

11. Conductor material that allows charges to move about easily Insulator material through which charges will not easily move Basic Law of Electrostatics Like charges repel; unlike charges attract

12. Conduction and Induction Induction – no touchConduction - touch

13. Induction vs Conduction

14. 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. induction does not When charging by induction, the rod does not touch touch the electroscope. The electroscope gets opposite charge the opposite charge of the rod.

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

18. A typical lightning bolt has about 10.0 C of charge. How many excess electrons are in a typical lightning bolt? 1 C = charge on 6.25 x 10 18 electrons 10 C = 6.25 x 10 19

19. 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.

20. 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

21. The electron and proton of a hydrogen atom are separated, on average, by a distance of about 5.3x10 -11 m. Find the magnitude of the electric force each particle exerts on the other. d = 5.3x10 -11 m k = 9.00 x 10 9 N m 2 /C 2 q e = -1.6x10 -19 C q p = 1.6x10 -19 C F  k q1q1 q2q2 d2d2 F e = -8.2x10 -8 N Attractive Force

22. Electric Fields An electric field exists in a region of 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).

23. The direction of the electric field at any point is defined to be the same direction as the direction of force on a positive test charge placed in the region at that point. Field lines point away from positive and toward negative charges.

24. Positive charge Lines of force are drawn perpendicular to and away from a positive object. +

25. Negative Charge Lines of force are drawn perpendicular to and into a negative object. -

26. Positive and Negative + - -

28. 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.

29. Sharing of Charge Charges move until all parts of a conductor are at the same potential. Two same size spheres: Before:After: _ _ _ _ _ _ _ _ _ _ AB _ _ _ _ _ _ _ _ _ _ Note: The net charge in the “system” does not change.

30. _ _ _ _ _ Different Size, Same Charge Before (Equal charges): After (Equal potential): _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Low VHigh V Low qHigh q

31. Notes The greater the surface area, the greater the spread between charges. The less the repulsive force, the less the potential. When touching, charges move to the sphere with the lower potential

32. Grounding Touching an object to Earth to eliminate excess charge. Never remove the third prong!

34. Electric Fields Near Conductors All charges are on the surface of a solid conductor Excess charges will move to the outer surface of a hollow conductor. Application: –Car acts as a hollow sphere, protecting occupants.

36. Electric Fields Near Conductors Electric Fields are largest near sharp points. Electric Fields depend on the shape of the body and its potential. _ _ _ _ _ _ _ _ _ Stronger electric field, but same potential _ _ _ _ _ _ _ _ _ __ _ _ __ _ _ _ _ _ _

37. Lightning & Lightning Rods

38. Steeples aren’t lightning rods! But they need to be!

39. Storing Charges - Capacitor Leyden Jar (1746) was used to store charge. For a given shape and size of an object, q/v = constant. This constant is called capacitance, C, of the object.

40. Capacitor Device to store charges Made up of two conductors, separated by an insulator. The two conductors have equal and opposite charges.

41. Equation Where:C = Capacitance (in Farads = Coulomb/Volt) q = amount of charge on capacitor V = potential difference.

43. Lesson 3

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

45. 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”.

46. 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

47. Battery (cells) A battery produces electricity by transforming chemical energy into electrical energy

48. Battery Carbon Electrode Zinc Electrode Sulfuric Acid +

50. Potential Difference

52. Electric current is measured in Amperes, in honor of Andre Marie Ampere Andre Marie Ampere Andre 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 IQtI = Q/tIQtI = Q/t

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

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

56. 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 Ohm  Ohm, , 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.

57. 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

58. Resistance and Temp

59. Resistance and Thickness

60. Resistor An electronic element that provides a specified resistance. A current or voltage REGULATOR

61. Resistivity The resistivity, , 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 =   = resistivity, usually in units of   cm l l = length, measured in cm A A = cross-sectional area, measured in cm 2

62. 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.

63. 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.

64. Types of Current AC  Alternating current  charges continuously change direction forward and back at 60 Hz Example: outlets (approx 120 V) DC  Direct current  charges move in one direction Example: batteries AC-DC Debate births the Electric Chair

67. Have you ever wondered why the birds that sit on power lines don’t get electric shocks? –It’s because the electricity is always looking for a way to get to the ground, but the birds are not touching the ground or anything in contact with the ground.