UNIT
E
Review
SUGGESTED ANSWERS
WHAT DO YOU REMEMBER?
1.
(c)
2.
(a)
3.
(b)
4.
(d)
5.
(d)
6.
(b)
7.
(c)
8.
(b)
9.
(a)
10.
(d)
11.
(d)
12.
(d)
13.
(a)
14.
(b)
15.
(a)
16.
(c)
17.
(a)
18.
(b)
19.
True
20.
False. Nuclear power relies on uranium, a non-renewable resource, to generate electricity.
21.
False. Electrostatic dusters use the process of charging by friction to attract dust.
22.
False. A generator does require an external energy source to generate electrical energy.
23.
False. AC is a flow of electrons in two directions.
24.
True
25.
False. To make an object positively charged, you should remove electrons from it.
26.
False. When the number of positive charges exceeds the number of negative charges, the object is
considered positive.
27.
False. A discharge occurs when two oppositely charged objects are brought together.
28.
True
29.
True
30.
False. The use of coal to produce electrical energy is considered to have a large environmental impact.
31.
False. Using uranium to generate electrical energy does contribute to climate change.
32.
False. Solar cells use energy from the Sun to produce electricity directly.
33.
True
34.
False. Ammeters measure electric current and are connected in series to a circuit.
35.
True
36.
False. An electrical load converts electrical energy to do something useful.
37.
False. Dividing the potential difference by the current will give you the resistance of a load.
38.
False. The total resistance of a circuit decreases by adding more loads in parallel.
39.
electric discharge
40.
ammeter
41.
direct current
42.
gaining
43.
does not
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44.
ground; grounding
45.
contact
46.
atomic nuclei
47.
Sun
48.
parallel; series
49.
potential difference; parallel
50.
slope
51.
the same
52.
the same
53.
release
54. (a)(i); (b)(iii); (c)(v); (d)(ii); (e)(iv)
WHAT DO YOU UNDERSTAND?
55.
Charge
Location in Atom
Ability to Move
(a) neutrons
no charge
in the nucleus
do not move
(b) protons
charge of 11
in the nucleus
do not move
(c) electrons
charge of 21
found in energy levels
around the nucleus
easy to move in
some materials
56. (a)
57.
To make an object neutral, connect the object to the ground with a conducting wire.
(b)
To make an object positively charged, attach a grounding wire to the neutral object. Then bring a
negatively charged object close so that both objects are very close or touching. Remove the grounding
wire while the two objects are close or touching.
(c)
To make an object negatively charged, bring a negatively charged object close so that both objects
are touching.
Objects with like charges repel; objects with unlike charges attract.
58.
ⴙⴚ
ⴚⴙⴙ
ⴙⴚ ⴚ
ⴚⴙ ⴙ
ⴚ
Rodⴙⴚ
iveⴚⴚⴚ
ⴚ
t
a
ⴙ ⴚⴚ
Neg ⴙ
ⴚⴚ
ⴚⴚ
neutral ball
ground
negative
rod drives
electrons
to ground
by induction
ⴙⴚ
ⴚⴙⴙ
ⴙⴚ ⴚ
ⴚⴙ ⴙ
ⴚ
ⴙⴙ ⴙ
ⴙ
ⴙ ⴙ
remove rod
positive
charge
left on
ball
remove
ground
ground
ground
59.
Metals are good conductors of electricity. As a result, lightning can travel easily and safely through the
metallic rod to the ground.
60.
The rest of the energy is converted into thermal energy, or heat.
61.
The voltage drop across each load decreases as the number of loads in the series circuit increases.
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62.
After
Before
ⴚ
ⴙ
ⴚ
ⴙ
ⴚ
ⴚ
ⴙ
ⴚ
63.
64.
ⴚ
ⴙ
ⴚ ⴚ ⴙ
ⴙ ⴚ ⴙ
ⴚ
ⴙ
ⴚ
ⴙ
ⴚ
ⴚ
ⴙ
ⴚ
ⴙ
ⴙ
ⴚ
ⴙⴚ
ⴙⴚ
ⴚ
Resistance (Ω)
Voltage (V)
Current (A)
Circuit A
36
90
2.5
Circuit B
350
175
0.5
Circuit C
150
120
0.8
A toaster oven is much smaller than a regular oven, so it requires less energy to attain a temperature high
enough to heat a pizza slice. Because a slice of pizza could probably fit in a toaster oven, it would be more
efficient to use the toaster oven for this task.
SOLVE A PROBLEM
65.
Touch the electroscope with a negatively charged conductor.
66.
You have been given some fur, an ebonite rod, a glass rod, and a piece of polyester. Your teacher asks you to
charge the objects by friction. What combinations will you use? Explain why this will work.
Fur is above glass and polyester is above ebonite in the electrostatic series. So to make the glass rod
negatively charged, rub it with fur. To make the ebonite rod negatively charged, use either fur or polyester.
67. (a)
(b)
68. (a)
(b)
69. (a)
The electroscope leaves are apart and have a negative charge. The electroscope overall is still neutral;
this means the charging is by induction. So a negatively charged object must be inducing the negative
charge on the electroscope.
The pith ball overall is neutral and the charges are randomly distributed. So a neutral object must have
been brought near an already neutral pith ball.
Series circuit: V1 5 V2 5 V3 5 6.0/3 5 2.0 V. I1 5 I2 5 I3 5 1.0 A.
Parallel circuit: V1 5 V2 5 V3 5 6.0 V. I1 5 I2 5 I3 5 1/3 5 0.33 A.
Series circuit: total resistance: RT 5 Vsource/Isource 5 6.0/1.0 5 6.0 Ω
resistance of each lamp: R1 5 V1/I1 5 2.0/1.0 5 2.0 Ω
(b)
Parallel circuit: total resistance: RT 5 Vsource/Isource 5 6.0/1.0 5 6.0 Ω
resistance of each lamp: R1 5 V1/I1 5 6.0/0.33 5 18 Ω
70.
(75–0)/(1.2–0) 5 62.5 Ω
The resistance is 62.5 Ω.
71.
V/I 5 115/12.0 5 9.58 Ω
The resistance of the toaster is about 9.6 Ω.
72.
I 5 V/R 5 3.6/50.0 5 0.072 A or
The current going through this circuit is 72 mA.
73.
V 5 IR 5 (0.020)(75) 5 1.5 V
The voltage drop across the watch’s battery is 1.5V
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74.
Electronic items may come in contact with charged objects during shipping, which could damage
the items. Anti-static bags enclose electronic items and prevent them from being damaged by electric
discharges.
75. (a)
(b)
76.
Power (W)
Time per
Month (h)
kW·h per
month
Cost
Television
210
20
4.20
$0.50
Computer
150
32
4.8
$0.58
Video Game
System
180
8
1.44
$0.17
24 h/day 3 30 days/month 5 720 h/month; 720 h/month 3 0.15 kW 5 108 kW . h/month.
The dam will change the way the river flows in the area. Some aquatic animals may not be able to migrate
properly. The dam could also cause major flooding, which would force communities to relocate. The dam
would very likely cause a water shortage in areas that previously had access to water from the river.
Create and Evaluate
77. The manufacturer could start by increasing the efficiency of their products, so the useful energy out is as
close as possible to the energy in. One way this might be done would be to use copper wiring instead of
aluminum in the device, because copper is a better conductor than aluminum. Making devices as light and
small as possible also usually saves electricity. Also, a switch on the device that truly turns off the power
instead of keeping the device on standby could save a lot of electricity. On the manufacturing side, savings
inside the factory could be made in similar ways—using electrically efficient equipment, developing a
better manufacturing process that uses less resources and recycles waste products, and shutting off power
when not needed. The company could also produce some or most of its electricity using renewable
resources such as solar or wind. If the company doesn’t have enough money to buy solar panels or a wind
turbine, they could buy electricity from a supplier that produces “green” electricity.
78.
The use of sensors that shut off lights and other electrical devices when they detect no one is in a room
could save electricity. Other ways to reduce electrical energy consumption are to buy energy-efficient
appliances, operate washing machines only if you have full loads, dry clothes on a clothes line, do more
activities during the daytime or in rooms with more natural light to reduce the need for artificial lights,
and avoiding the use of devices that are not necessary.
79.
Non-renewable resources are the traditional types of resources used to generate electrical energy. The
technology has been used for a long time and represents a huge existing investment. It will take time
before alternative renewable sources can replace them. Government policies have a lot to do with why we
continue to use non-renewable resources.
80.
Like any technology, there are difficulties with renewable energy sources. Solar panels are very expensive
and require appropriate government policies to make their widespread use successful. They also produce
electricity slowly, over the course of a day. Wind turbines and towers are expensive. Geothermal and tidal
sites are few in number and require appropriate sites. Biomass generation could require the turning over of
land for food production to energy production.
81.
Check to see that students’ designs incorporate information about static electricity. For example, students
could create a design that includes materials, such as polyester, that would attract hair. Students should
justify their choice of materials by explaining how charge accumulates on the material, and how that
charge could be used to attract dust. Students’ diagrams should show a charged object attracting dust
particles.
82.
The design will probably rely on current electricity, because this type of electricity can be readily controlled
through an electrical circuit. The circuit will include a load that converts electrical energy into thermal
energy. Static electricity, on the other hand, is not as easily controlled, so it would not be appropriate for
this design.
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83.
ⴙ
ⴚ
84.
Sample answer: I would construct a simple circuit using the battery, the light bulb, and the cooper wire.
I would then splice the wire to make a place where the material being tested could be inserted (with
copper wire attached to each end). After the insertion of each material being tested, I would check to see
if a current could travel through the circuit by seeing if the light bulb lights up. If the light bulb lights, the
material is a conductor; if the light bulb fails to light, the material is an insulator.
REFLECT ON YOUR LEARNING
85.
Sample answer: I support the use of renewable energy sources to produce electricity, as well as energy
conservation. My classmates tend to agree that conservation is easier to accomplish than substituting
renewable energy sources for non-renewable ones. To conserve, we can cut down on electricity use and be
smart about using it. To get renewable energy for our community, we will need to push governments to
change energy policies. To do this, we
86. (a)
(b)
Sample answer: Electricians and computer technicians are two occupations that directly apply an
understanding of electricity.
Sample answer: Yes, I plan to be a forensics investigator. Forensics investigators apply knowledge of
electricity when they use electrostatic lifting to make copies of footprints.
WEB CONNECTIONS
87.
Sample answer: I would require each minister to be extremely creative and “think outside the box.”
I would want that each minister is honest and strong-willed to do what is “right,” rather than do what is
easy. I would also want each minister to think long-term and have a clear vision of the “big picture,” rather
than focus on ineffective band-aid solutions. Each minister should be well-educated in the science and the
business side of each ministry.
The Minister of Energy would need to know the costs and benefits of all energy options in economic,
environmental, and social terms. He or she would need to appreciate the urgency of issues like climate
change and oil depletion. That said, the minister would also need to be smart and creative to figure out
ways to actively engage citizens to make them part of the solution.
The Minister of Transportation would have to know how to be smart about making better use of our
transportation infrastructure. The minister would have to figure out the best ways to move the most people
with the least resources and the least on-going infrastructure cost. This would mean trains would have to
become the main form of transportation, not cars. The minister would encourage people to live where
they work to reduce long distance travel. This would result in less traffic and smaller communities having
improved economies.
The Minister of Natural Resources would have to be creative to find ways to make the most of limited
resources. Thinking long-term would be critical because environmental costs are very significant. If the
minister creates the appropriate government policies, renewables can have a fair footing in the marketplace.
The minister must know how to get as many citizens personally involved in reducing their energy use
and their use of other resources. Financial barriers need to be dealt with; otherwise, nothing will change.
Technical expertise would need to be combined with common sense and compassion.
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