1. Electric charge is responsible for clothes that stick together when they are removed from a dryer.

2. Electric Charge
What produces a net electric charge?
An excess or shortage of electrons produces a net electric charge.

3. Electric Charge
Electric charge is a property that causes subatomic particles such as protons and electrons to attract or repel each other.
Protons have a positive charge.
Electrons have a negative charge.

4. Electric Charge
In an atom, a cloud of negatively charged electrons surrounds the positively charged nucleus. The atom is neutral because it has equal numbers of positive and negative charges.
If an atom gains electrons, it becomes a negatively charged ion.
If an atom loses electrons, it becomes a positively charged ion.

5. A neutral atom has equal numbers of protons and electrons.
Electric Charge
A neutral atom has equal numbers of protons and electrons.
Proton
Neutron

6. The SI unit of electric charge is the coulomb (C).
It takes about 6.24 × 1018 electrons to produce a single coulomb.
A lightning bolt is about 10 to 20 coulombs of charge, and a camera flash is about coulombs.

7. Electric Forces
What determines whether an electric force is attractive or repulsive?
Like charges repel, and opposite charges attract.

8. Electric Forces
The force of attraction or repulsion between electrically charged objects is electric force.
The electric force between two objects is directly proportional to the net charge on each object.
The electric force is inversely proportional to the square of the distance between the objects.

9. Electric Forces Opposite charges attract each other.
Doubling one charge doubles the force on both charges.
Like charges repel. Doubling the distance makes the force one fourth as great.

10. Electric Fields
What determines the strength of an electric field?
The strength of an electric field depends on the amount of charge that produces the field and on the distance from the charge.

11. The electric field around a positive charge points outward.
Electric Fields
The electric field around a positive charge points outward.
The electric field around a negative charge points inward.
Field of a positive charge
Field of a negative charge

12. Static Electricity and Charging
What are three ways in which charge is transferred?
Charge can be transferred by friction, by contact, and by induction.

13. Static Electricity and Charging
Static electricity is the study of the behavior of electric charges.
According to the law of conservation of charge, the total charge in an isolated system is constant. When there is a charge transfer, the total charge is the same before and after the transfer occurs.

14. Static Electricity and Charging
Charging by Friction
Rubbing a balloon on your hair causes charging by friction.
Electrons move from your hair to the balloon because atoms in rubber have a greater attraction for electrons than atoms in hair.
The balloon picks up a net negative charge.
Your hair loses electrons and becomes positively charged.

15. Static Electricity and Charging
Charging by Contact
A Van de Graaff generator builds a charge on a metal sphere. Touching the sphere transfers charge by contact.
The sphere is still charged, but its net charge is reduced.

16. Static Electricity and Charging
Charging by Induction
Walking on a carpet builds a negative charge on your body. The negative charge in your hand repels electrons in a metal doorknob.
The doorknob is still neutral, but charge has moved within it. This is induction, a transfer of charge without contact between materials.

17. Assessment Questions
Which of the following would double the electric force between two charged objects?
doubling the mass of the objects
doubling the net charge of both objects
doubling the net charge of one of the objects
cutting the distance between the objects in half

18. Assessment Questions
Which of the following would double the electric force between two charged objects?
doubling the mass of the objects
doubling the net charge of both objects
doubling the net charge of one of the objects
cutting the distance between the objects in half ANS: C

19. Assessment Questions
The attractive or repulsive effect an electric charge has on other charges in the space around it is the charge’s
electric force.
electric field.
static electricity.
static discharge.

20. Assessment Questions
The attractive or repulsive effect an electric charge has on other charges in the space around it is the charge’s
electric force.
electric field.
static electricity.
static discharge. ANS: B

21. An object becomes charged by induction when there is a
Assessment Questions
An object becomes charged by induction when there is a
transfer of electrons, as the object rubs against another object.
transfer of charge, as it contacts another charged object.
transfer of charge by motion of electrons within the object.
a sudden movement of electric charge from another object.

22. An object becomes charged by induction when there is a
Assessment Questions
An object becomes charged by induction when there is a
transfer of electrons, as the object rubs against another object.
transfer of charge, as it contacts another charged object.
transfer of charge by motion of electrons within the object.
a sudden movement of electric charge from another object. ANS: C

23. An electric current can only flow when there is a closed path in which electrons can move.

24. Electric Current
What are the two types of current?
The two types of current are direct current and alternating current.

25. The continuous flow of electric charge is an electric current.
Charge flows only in one direction in direct current (DC). A flashlight and most other battery-operated devices use direct current.
Alternating current (AC) is a flow of electric charge that regularly reverses its direction. Electric current in your home and school is mostly alternating current.

26. Electric Current
The SI unit of electric current is the ampere (A), or amp, which equals 1 coulomb per second.
Even though electrons flow in an electric current, scientists define current as the direction in which positive charges would flow.

27. Conductors and Insulators
What are some examples of conductors and insulators?
Metals such as copper and silver are good electrical conductors. Wood, plastic, rubber, and air are good electrical insulators.

28. Conductors and Insulators
An electrical conductor is a material through which charge can flow easily.
An electrical insulator is a material through which charge cannot flow easily.
A metal wire is usually coated with plastic or rubber.
The metal wire is an electrical conductor.
The rubber and plastic are electrical insulators.
The coating around a wire helps to control the current and keep it where it is needed.

29. Resistance
What factors affect electrical resistance?
A material’s thickness, length, and temperature affect its resistance.

30. Resistance is opposition to the flow of charges in a material.
As electrons move through a conducting wire, they collide with electrons and ions. These collisions convert some kinetic energy into thermal energy, and the current is reduced.
The SI unit of resistance is the ohm.

31. Resistance
Using a thick straw to drink a milkshake is easier than using a thin straw. Similarly, electrons flow more easily through a thick wire than they flow through a thin wire of the same material.
metal ions
electron

32. Resistance
Resistance is greater in a longer wire because the charges travel farther. As temperature increases, a metal’s resistance increases because electrons collide more often.
A superconductor is a material that has almost zero resistance when it is cooled to low temperatures.

33. Voltage
What causes an electric current?
In order for charge to flow in a conducting wire, the wire must be connected in a complete loop that includes a source of electrical energy.

34. Voltage Potential Difference
Water falls spontaneously from a higher to a lower height. Likewise, electric charges flow from a higher to a lower potential energy.
Potential difference is the difference in electrical potential energy between two places in an electric field.
Potential difference is measured in joules per coulomb, or volts. Because it is measured in volts, potential difference is also called voltage.

35. Voltage
Voltage Sources
A source of voltage does work to increase the potential energy of electric charges. Three common voltage sources are batteries, solar cells, and generators.
A battery is a device that converts chemical energy to electrical energy.

36. Ohm’s Law
How are voltage, current, and resistance related?
Increasing the voltage increases the current. Keeping the same voltage and increasing the resistance decreases the current.

37. Ohm’s Law
According to Ohm’s law, the voltage (V) in a circuit equals the product of the current (I) and the resistance (R).
When the current is in amperes, and the resistance is in ohms, the voltage is in volts.

38. Ohm’s Law
What is the voltage if the resistance is 3 ohms and the current is 3 amps?
V = I × R = 3 amps × 3 ohms = 9 volts

39. Assessment Questions
Which of the following materials is a good conductor of electric current?
wood
glass
air
iron

40. Assessment Questions
Which of the following materials is a good conductor of electric current?
wood
glass
air
iron ANS: D

41. Assessment Questions
If a piece of wire has a certain resistance, which wire made of the same material will have a lower resistance?
a hotter wire
a thicker wire
a longer wire
a thinner wire

42. Assessment Questions
If a piece of wire has a certain resistance, which wire made of the same material will have a lower resistance?
a hotter wire
a thicker wire
a longer wire
a thinner wire ANS: B

43. Assessment Questions
What does the voltage between two points in an electric field represent?
the total kinetic energy
the difference in mechanical energy
the difference in potential energy
the electrical energy

44. Assessment Questions
What does the voltage between two points in an electric field represent?
the total kinetic energy
the difference in mechanical energy
the difference in potential energy
the electrical energy ANS: C

45. Assessment Questions
A 9-volt battery drives an electric current through a circuit with 4-ohm resistance. What is the electric current running through the circuit?
0.44 A
2.25 A
5 A
36 A

46. Assessment Questions
A 9-volt battery drives an electric current through a circuit with 4-ohm resistance. What is the electric current running through the circuit?
0.44 A
2.25 A
5 A
36 A ANS: B

47. Assessment Questions
The two types of electric current are direct current and indirect current. True False

48. Assessment Questions
The two types of electric current are direct current and indirect current. True False
ANS: F, alternating

49. Circuit Diagrams
What is included in a circuit diagram?
Circuit diagrams use symbols to represent parts of a circuit, including a source of electrical energy and devices that are run by the electrical energy.

50. An electric circuit is a complete path through which charge can flow.
Circuit Diagrams
An electric circuit is a complete path through which charge can flow.
A circuit diagram shows one or more complete paths in which charge can flow.
Arrows show the direction of current, from positive to negative. The direction of current is defined as the direction in which positive charges would flow, but electrons flow in the opposite direction.

51. Series Circuits
How do series and parallel circuits differ?
If one element stops functioning in a series circuit, none of the elements can operate.
If one element stops functioning in a parallel circuit, the rest of the elements still can operate.

52. Series Circuits
In a series circuit, charge has only one path through which it can flow.
If one bulb burns out in a series circuit, it becomes an open circuit.
The bulbs in a circuit are a source of resistance. Adding bulbs to a series circuit increases the resistance. The current decreases, and each bulb shines less brightly.

53. Series Circuits
A series circuit has one path that each charge can follow.

54. Parallel Circuits
A parallel circuit is an electric circuit with two or more paths through which charges can flow.
If one bulb in a parallel circuit burns out, charge still flows along the other path, and the other bulb stays lit.
In a home, electric circuits are wired in parallel so they can operate independently.

55. Parallel Circuits
A parallel circuit has more than one path each charge can follow.

56. Power and Energy Calculations
How do you calculate electric power and electrical energy use?
Electric power can be calculated by multiplying voltage by current.

57. Power and Energy Calculations
The rate at which electrical energy is converted to another form of energy is electric power. Recall that power is the rate of doing work.
The unit of electric power is the joule per second, or watt (W). Power often is measured in thousands of watts, or kilowatts (kW).
P (Power) =I (amps)X V(volts)

58. Power and Energy Calculations
Calculating Electric Power
An electric oven is connected to a 240-volt line, and it uses 34 amps of current. What is the power used by the oven?

59. Power and Energy Calculations
Plan and Solve
Replace each variable with its known value.

60. Power and Energy Calculations
1. A clothes dryer uses about 27 amps of current from a 240-volt line. How much power does it use? Answer:

61. Power and Energy Calculations
1. A clothes dryer uses about 27 amps of current from a 240-volt line. How much power does it use? Answer: P = I × V = (240 V)(27 A) = 6500 W

62. Power and Energy Calculations
2. A camcorder has a power rating of 2.3 watts. If the output voltage from its battery is 7.2 volts, what current does it use? Answer:

63. Power and Energy Calculations
2. A camcorder has a power rating of 2.3 watts. If the output voltage from its battery is 7.2 volts, what current does it use? Answer: I = P/V = (2.3 W)/(7.2 V) = 0.32 A

64. Power and Energy Calculations
3. A power tool uses about 12 amps of current and has a power rating of 1440 watts. What voltage does the tool require? Answer:

65. Power and Energy Calculations
3. A power tool uses about 12 amps of current and has a power rating of 1440 watts. What voltage does the tool require? Answer: V = P/I = (1440 W)/(12 A) =120 V

66. Power and Energy Calculations
An appliance's power rating lets you know how much power it uses under normal conditions. An electric stove uses about 6000 watts, and a microwave oven uses about 1000 watts.
Find the electrical energy used by an appliance by multiplying power by time.

67. Power and Energy Calculations
The power rating of a typical clothes dryer is 5400 watts, or 5.4 kilowatts. If you use the clothes dryer for 2 hours, the energy use is 5.4 kilowatts multiplied by 2 hours, or 10.8 kilowatt-hours.
A kilowatt-hour equals 3,600,000 joules.

68. Electrical Safety
What devices make electricity safe to use?
Correct wiring, fuses, circuit breakers, insulation, and grounded plugs help make electrical energy safe to use.

69. Electrical Safety
Home Safety
A fuse prevents current overload in a circuit. A wire in the center of the fuse melts if too much current passes through it.
A circuit breaker is a switch that opens when current in a circuit is too high. The circuit breaker must be reset before the circuit can be used again.

70. Electrical Safety
Fuses have an internal wire that burns out if a current is too great.

71. Electrical Safety
Insulation also prevents short circuits.
A three-prong plug can prevent shocks caused by short circuits. If a short circuit develops, the current takes an easier path to ground through the grounding wire.
The transfer of excess charge through a conductor to Earth is called grounding.

72. Even a small current in your body can cause a painful shock or injury.
Electrical Safety
Even a small current in your body can cause a painful shock or injury.
Ground-fault circuit interrupter (GFCI)

73. Assessment Questions
A number of light bulbs are connected to an energy source in a series circuit. What will happen to the other bulbs if one of the bulbs burns out?
Nothing will happen.
They will be brighter.
They will be dimmer.
They will turn off.

74. Assessment Questions
A number of light bulbs are connected to an energy source in a series circuit. What will happen to the other bulbs if one of the bulbs burns out?
Nothing will happen.
They will be brighter.
They will be dimmer.
They will turn off. ANS: D

75. Assessment Questions
A pair of 15-watt computer speakers are connected to a 12-volt power supply. What is the electric current running through the speakers?
0.8 A
1.25 A
12.5 A
180 A

76. Assessment Questions
A pair of 15-watt computer speakers are connected to a 12-volt power supply. What is the electric current running through the speakers?
0.8 A
1.25 A
12.5 A
180 A ANS: B

77. Assessment Questions
A ground-fault circuit interrupter is a switch that opens to prevent overheating when the current in a circuit is too high. True False

78. Assessment Questions
A ground-fault circuit interrupter is a switch that opens to prevent overheating when the current in a circuit is too high. True False
ANS: F, circuit breaker