1. Electricity

2. 20.1 Electric Charge & Static Electricity

3. Force
Electric forces – attractive or repulsive
What does this mean?

4. Opposites attract

5. Like charges repel

6. And remember….

7. Electric Fields Strength of a field depends on:
the charge produced by the field
the distance of field

8. Static Electricity DEFINITION:
Net accumulation of electric charges on an object.
IN OTHER WORDS:
Electrons that are moved from 1 place to another usually by rubbing, brushing or no contact.

9. Static charges work 3 ways
Friction
Contact
Induction

10. Friction
Since opposite charges attract, the electrons move from the hair to the comb.
The comb is now negatively charged by FRICTION.

11. For the visual learners . . .

12. Contact
Van deGraaff generator has a – charge at top. Touching top would make the object – charged.
The object is now negatively charged by CONTACT.

13. Induction
- charges in hand cause the + charges in the doorknob to move to the opposite side (opposites attract)
Charge has been transferred by INDUCTION.

14. For the visual learners….

15. Static Discharge
When a pathway that charges can move through forms suddenly.
Ie: lightening, touching a doorknob

16. Attract or Repel?
Attract

17. Attract or Repel?
Repel

18. What’s the best thing about static electricity?

20. Lecture 20.2
                       
You need a calculator

21. 20.2 Electric Current & Ohms’s Law

22. Current The flow of electrons through a wire or a conductor.
SI unit = (Amps) A

23. 2 types of current A/C – alternating current D/C – direct current
ie: by plugging into the
household wiring
D/C – direct current
ie: batteries

24. Conductor
DEFINITION: Material that allows electrons to move easily through it.
IN OTHER WORDS: Just like a train conductor moves cars from one track to another track, conductors move electrons from one place to another.

25. Which metal is the best conductor for your internet connection?

26. Copper?
Silver?

27. Insulator
DEFINITION: Material that does not allow electrons to move through it.
IN OTHER WORDS: Just as a potholder insulates you from heat, electrical insulators slow down or resist the flow of electricity.

28. Conductor or Insulator ?
Glass

29. Conductor or Insulator ?

30. Conductor or Insulator ?
Ceramic

31. Conductor or Insulator ?

32. Conductor or Insulator ?
Copper

33. Conductor or Insulator ?

34. Conductor or Insulator ?
Wood

35. Conductor or Insulator ?
Although uncommon, there are a number of insulator styles made from wood.  One type was made from the dense wood lignum vitae for the San Francisco trolley system.

36. Everyday examples of conductors and Insulators

37. To sum them up….. silver glass copper rubber gold oil aluminum asphalt
Conductors:
silver
copper
gold
aluminum
iron
steel
brass
bronze
mercury
graphite
dirty water
concrete
Insulators:
glass
rubber
oil
asphalt
fiberglass
porcelain
ceramic
quartz
(dry) cotton
(dry) paper
(dry) wood
plastic
air
pure water

38. Mini Quiz The build up of charges on an object is called?
Electrons do not move through…
Electrons move easily through materials called …
Static Electricity
Insulators
Conductors

39. Resistance
DEFINITION: the tendency for a material to oppose the flow of electrons, changing energy into thermal energy and light.
SI unit = Ohm’s (W)
See pg Fig. 8

40. What effects resistance?
Temperature
Thickness
Length

41. Think of a common household item that has a resistor
Something we
use in class?

42. Potential Difference - Voltage
DEFINTION: Difference in potential between 2 different places.
IN OTHER WORDS:
It is the amount of work that must be done to carry a charge from one point to another.

43. A source of potential difference must keep the current flowing.

44. Ohm’s Law Potential difference = current x resistance
V (volts) = I (amperes) x R (ohms)
Compare to: Water in a Hose
Electricity is:
DC in a Wire
Electrical Units
Symbol
pressure
potential (V)
Volts V
rate of flow
current (I)
Amps (or Amperes) A
friction
resistance (R)
Ohms W

45. How do you remember the formula?
…..if this helps, use it.

47. Practice problems resistance – R = 75 ohms voltage – V = 110 volts
A 75 ohm circuit is powered by a 110-Volt energy source.  What is the current flowing in this circuit?
First we identify the information that we are given in the problem:
resistance – R = 75 ohms
voltage – V = 110 volts
Need to know amps
110V = I x 75 ohms (rearrange formula)
Amps = 110 volts / 75 ohms (W)
1.5A

48. Practice problems resistance = 250 ohms current = 0.95 amps
What is the voltage of a circuit with a resistance of 250 ohms and a current of 0.95 amps?
First we identify the information that we are given in the problem:
resistance = 250 ohms
current = 0.95 amps
Need to know volts
V= 250 ohms x 0.95 amps
Volts = 250 ohms x 0.95 amps
237.5V

49. Mini Quiz ___ is a flow of electrons thru a wire or conductor. Current
A current must have a constant flow of ___
Current
Potential Difference

50. Mini Quiz Tendency for a material to oppose the flow of electrons
What 3 quantities are related to Ohm’s Law
Resistance
Voltage, current, and resistance

51. Review Quiz of 20.2 before next section
View here

52. 20.3
20.3 Electric Circuits

53. Circuit is a closed path through which electrons can flow.

54. Circuit Symbols

55. Series Circuit Christmas lights are often wired this way.
Disadvantage – when 1 light goes out the whole strand goes out.

56. Series Circuit

57. Parallel Circuit Electricity has several paths that it can travel.
Used in households. When one circuit is closed others still work.

58. Parallel Circuit

60. Series or Parallel?
Parallel

61. Series or Parallel?
Series

62. Power = current x voltage
Electrical Power
Expressed in watts (W) or kilowatts (kW)
The amount of power an appliance used can be calculated by
Power = current x voltage
Watts = amps x volts
P = I x V

63. Power is expressed here as E for “energy”

65. Mini Quiz A _____ is a closed path in which electrons flow Circuit
Christmas lights are an example of …..
Household wiring are wired by …
Circuit
Series Circuit
Parallel Circuits

66. Number your paper 1-9. View here
Video quiz
Number your paper 1-9.
View here

67. Check your answers 9. Swimming pool 1. c) electrons Open area
Climbing on a metal ladder
Fishing in a metal boat on a lake
Standing in a field wearing a metal suit
1. c) electrons
2. a) nucleus
3. b) insulators
4. c) electrical
5. b) attract
6. c) positive
7. b) neutral
8. d) negative

68. The End

69. Electroscope
An instrument for detecting the presence of static electricity.
When the leaves are charged the same way they repel each other.