1. Chapter 17: Introduction to Electricity
Material on Final Exam

2. Section 17.1: Electric charge and Static Electricity
Electrical Charge
Atoms are made of three parts
Protons
Neutrons
Electrons
Focus on electrons

3. Section 17.1: Electric charge and Static Electricity
Charges Exert Forces
Three charge options
+, -, Ø
Charges exert forces
Law of Electrical charges states that like charges repel and opposite charges attract

5. Section 17.1: Electric charge and Static Electricity
What is happening in A? B? C?

6. Section 17.1: Electric charge and Static Electricity
PROCESS BOX
In the space below, explain the law of electrical charges in your own words. You need at least 2 lines.
Stamp
Spot!

7. Section 17.1: Electric charge and Static Electricity
Electrical Force and Electrical Fields
Electrical forces are forces of attraction or repulsion on a charged particle that is due to an electric field
Two factors
Charge size
Charge distance

8. Section 17.1: Electric charge and Static Electricity

9. Section 17.1: Electric charge and Static Electricity
An electrical field is the space around a charged object in which another charged object experiences an electrical force

10. Section 17.1: Electric charge and Static Electricity
Charge it!
How to get a charge?
Change # or position of electrons!
3 ways
Friction
Conduction
Induction

11. Section 17.1: Electric charge and Static Electricity
Friction
Electrons are “wiped” from one source to another
Creates charge

12. Section 17.1: Electric charge and Static Electricity
Conduction
A charged substance comes in direct contact with another substance
Creates charge by transfer

13. Section 17.1: Electric charge and Static Electricity
Induction
A charged substance comes indirectly charges another object
Creates charge

15. Section 17.1: Electric charge and Static Electricity
Conservation of charge
No charges are created or destroyed through these processes

16. Section 17.1: Electric charge and Static Electricity
PROCESS BOX
In the space below, explain how we can charge an item if we cannot create or destroy charge. You need at least 2 lines.
Stamp
Spot!

17. Section 17.1: Electric charge and Static Electricity
Detecting Charge
An electroscope is a device that detects charge
As charge is applied, moves charge to metal pieces and separates them

18. Section 17.1: Electric charge and Static Electricity
Conductors
An electrical conductor is a material in which charges can move freely
Electrons are free-moving
Copper, Aluminum, Magnesium

19. Section 17.1: Electric charge and Static Electricity
Insulator
An electrical insulator is a material in which charges cannot move freely
Electrons are “locked in” and cannot move
Plastic, rubber, glass, wood, air

20. Section 17.1: Electric charge and Static Electricity
PROCESS BOX
In the space below, explain why it is important to have both conductors and insulators in everyday life. You need at least 2 lines.
Stamp
Spot!

21. Section 17.1: Electric charge and Static Electricity
Static electricity is an electric charged produced by friction or induction
Called static no change
Item builds up charge and keeps it

22. Section 17.1: Electric charge and Static Electricity
Electric Discharge
Charges eventually leave
Electric Discharge is the release of electricity stored in a source
Can be slowly
Laundry
Can be quick
Door knob, car door
Lightning

23. Lightning

24. Section 17.2: Electric current and Electrical Energy
Energy of electrical charges

25. Section 17.2: Electric current and Electrical Energy
Electric current is the rate at which charges pass through a given point
If we INCREASE current, we INCREASE the number of charges per second
Units: Amperes Amps (A)
Calculations: I

26. Section 17.2: Electric current and Electrical Energy
Making Charges move
Very fast relay race of charges
Electrons move in field to destination

27. Section 17.2: Electric current and Electrical Energy
Current types
Alternating Current (AC)
Direct Current (DC)

28. Section 17.2: Electric current and Electrical Energy
Alternating Current AC
Charges move back and forth
Ex: outlets
Direct Current DC
All charges flow in same direction
EX: batteries

29. Section 17.2: Electric current and Electrical Energy
Voltage
Voltage is the potential difference between two points
The greater the voltage, the greater the current
Units: Volts (V)
Calculations: V

30. Section 17.2: Electric current and Electrical Energy
Resistance
Resistance is the opposition presented to the current by a material or device
“Electrical friction”
The greater the resistance, the less the current
Units: Ohms (Ω)
Calculations: R

31. Section 17.2: Electric current and Electrical Energy
Resistance Factors
There are 4 items that can affect the resistance of the wire
Material
Thickness
Length
Temperature
Check the last sheet of your packet for details!

32. Section 17.2: Electric current and Electrical Energy
Generating Electrical Energy
A cell is a device that produces an electric current by converting chemical or radiant energy into electrical energy
Parts of a cell
Electrolytes—chemical that allows charges to flow
Electrode—part of the cell where charges enter and exit

33. Cell Setup

34. Section 17.3 & 17.4: Electric Circuits and Calculations
Ohm’s Law
Georg Ohm ( ) first determined the relationship between current, voltage and resistance. According to Ohm’s Law, the voltage in a circuit equals the product of the current and the resistance.

35. Section 17.3 & 17.4: Electric Circuits and Calculations
Formula
Voltage – SI unit Volts
Current – SI unit Amps
Resistance – SI unit Ohm
V = IR V I R

36. Section 17.3 & 17.4: Electric Circuits and Calculations
Math Practice
What is the voltage if the current is 4 amps and the resistance is 10 ohms?
You try!
Find the voltage if the current is 0.2 A and the resistance is 2 ohms. I I R R
V = IR
V = 4 x 10
V = 40 Volts
V = IR
V = 0.2 x 2
V = .4 Volts

37. Section 17.3 & 17.4: Electric Circuits and Calculations
Math Practice
The resistance of an object is 4 ohms. If the current in the object is 9 A, what voltage must be used.
You try!
An object has the resistance of 20 ohms. Calculate the voltage needed to produce a current of 0.5 A. R R I I
V = IR
V = 0.5 x 20
V = 10 Volts
V = IR
V = 4 x 9
V = 36 Volts

38. Section 17.3 & 17.4: Electric Circuits and Calculations
Electric Power
Electric Power is the rate at which electrical energy is converted into other forms of energy
Where the “wattage” of our lights come from!

39. Section 17.3 & 17.4: Electric Circuits and Calculations
Formula
Power – SI unit Watts
Voltage– SI unit Volts
Current – SI unit Amps
P = VI P V I

40. Section 17.3 & 17.4: Electric Circuits and Calculations
Math Practice
A computer monitor draws 1.2A at a voltage of 120V. What is the power rating of the monitor?
You try!
What voltage would a light bulb have if the current is 0.5A and the power is 60W?

41. Section 17.3 & 17.4: Electric Circuits and Calculations
Electric Energy
The amount of electrical energy depends on the power of the electrical devices and the length of time that those devices are on

42. Section 17.3 & 17.4: Electric Circuits and Calculations
Formula
Energy – SI unit Joules
Power– SI unit Watts
Time – SI unit seconds
E = P x t E P t

43. Section 17.3 & 17.4: Electric Circuits and Calculations
Math Practice
How much energy is used if a 50W appliance is run for 5 seconds?
You try!
How much energy will be needed for a 200W appliance to run for 10 seconds?

44. Section 17.3 & 17.4: Electric Circuits and Calculations
Math Practice
What is the power of an appliance that uses 200,000 J of energy to run for 1000 seconds?
You try!
An appliance uses 5000J of energy to run for 4 seconds. What is the power?

45. Section 17.3 & 17.4: Electric Circuits and Calculations
Math Practice
How long will a 75W appliance run if it needs 150,000J?
You try!
A 5000J appliance uses 250 W. How long will it run for?

46. 20.3—Electric Circuits Electrical cost
Power companies usually charge by the kilowatt hour
Steps to find cost
Find energy: multiply appliance wattage by time (in hours)
Convert to kilowatt hours (either ÷ by 1000 or move decimal 3 times to the left)
Multiply by the cost from the electrical company
Round to two decimal places

47. 20.3—Electric Circuits
A 3000 watt air conditioner was used for 24 hours. What is the cost to run it that long if the electric company charges $0.05 per kilowatt-hour?

48. 20.3—Electric Circuits
Mr. Edison uses a 100W light bulb for an average of 150 hours per month. PECO charges them $0.15/kWh, what is the cost?

49. 20.3—Electric Circuits
I used a 900W coffee pot for 10 minutes to make coffee. If the cost is $0.07/kWh, what would the cost be to run the coffee pot?

50. Section 17.3 & 17.4: Electric Circuits and Calculations
An Electric circuit is a complete path around which charges can flow
There are 3 basic parts
Energy source
Wires (where charge flows)
Load (change electrical energy into other forms)

51. Section 17.3 & 17.4: Electric Circuits and Calculations
Series Circuit
Series Circuit
Series circuit has only one pathway for an electrical charge to flow.
If one element stops functioning in series circuit, none of the elements can operate.
Example – the wiring in a burglar alarm
1 Pathway

52. Section 17.3 & 17.4: Electric Circuits and Calculations
Parallel Circuit
Parallel Circuit
Parallel circuit is a electrical circuit with two or more paths through which charges can flow.
If one element stops functioning, the others can still operate.
Found in most homes and businesses
More than 1 path

53. Section 17.3 & 17.4: Electric Circuits and Calculations
PROCESS BOX
How are series and parallel circuits similar? How are they different? You need at least 2 lines.

54. Section 17.3 & 17.4: Electric Circuits and Calculations
Household Circuit Safety
Circuit breaker is a switch that opens when a current in a circuit is too high.
A strip of metal in the breaker warms up, bends, and opens the switch, which puts a gap in the current thus stopping the flow of charges
Fuse a thin piece of metal that melts or breaks when the current is too high.
Known as “blowing a fuse”
Grounding is the transfer of excess charge into the Earth
GFCI = Ground fault circuit interrupter

55. Section 17.3 & 17.4: Electric Circuits and Calculations