CHAPTER
12
Self-Quiz
SUGGESTED ANSWERS
1.
(b); Choice (b) is correct. Primary cells use irreversible chemical reactions to produce a flow of electrons.
Once these reactions have run to completion, the cell cannot produce electrical energy and must be
properly disposed of. Choices (a), (c), and (d) all describe characteristics of a secondary cell. A secondary
cell uses reversible chemical reactions to produce electrical energy. Recharging these cells reverses the
reaction and allows the cell to be used again to power a device
2.
(a); Choice (a) is correct. A watt is a unit used to measure electrical power. One watt is the equivalent of
one joule per second. Choice (b) is incorrect. A joule is a unit used to measure energy, including electrical
energy. Choice (c) is also incorrect. A kilowatt-hour is a unit of electrical energy that equals the amount
of energy consumed by a 1000-watt device in one hour. Choice (d) is incorrect. The percent efficiency is a
way to express how efficient a device is by comparing the energy the device produces with the energy the
device consumes.
3.
(b); Choice (b) is correct. The efficiency of a solar panel is based on the type of materials used to make it
and its ability to release electrons. Choice (a) is incorrect. Solar power is a renewable energy source that
comes from the Sun and is continually replenished. Choice (c) is also incorrect. Nuclear power plants, not
solar power farms, release hot water into nearby lakes. Choice (d) is incorrect because noise is a problem
with wind farms, not solar power farms.
4.
(b); Choice (b) is correct. In a nuclear power plant, neutrons collide with radioactive uranium, causing
uranium atoms to break apart and release huge amounts of energy in the process. Choice (a) is incorrect
because tidal power generation does not involve radioactive material. Instead, it uses the motion of tides to
turn the blades of a turbine, which are connected to a generator that produces electrical energy. Choice (c)
is also incorrect. Geothermal power generation uses the thermal energy from within Earth to produce
electrical energy. Choice (d) is incorrect because hydro-electric power generation uses the energy in falling
water to generate electrical energy.
5.
True. To produce electrical energy, nuclear reactors do not burn fuels that contribute to air pollution.
However, the mining, refining, and transportation of uranium does use fossil fuels that contribute to air
pollution. Nuclear generation also produces radioactive waste that can be dangerous if not stored properly.
6.
False. It costs more to produce electricity when demand is greatest, generally during the day from Monday
through Friday. A correct statement would be: Electricity is most costly to produce on weekdays from
9 a.m. to 5 p.m.
7.
chemical, electrical; A fuel cell combines hydrogen and oxygen in a chemical reaction that produces water.
The energy given off by this chemical reaction is converted into electrical energy that can be used to power
a vehicle.
8.
fossil fuels; fossil fuels, made up of compounds of carbon and hydrogen, were formed by the gradual
decomposition of dead organisms. Because they take millions of years to form, fossil fuels are considered
non-renewable resources.
9. (a)
(ii) A switch turns an electrical appliance on or off by completing or breaking the path of electron flow;
(b) (v)
Solar panels use photovoltaic cells to convert energy from sunlight directly into electrical energy;
(c) (iii) In scientific terms, a battery refers to a combination of two or more electric cells. In everyday
language, an electric cell is often referred to as a battery;
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(d) (i)
The load in an electric circuit can be a heater, light bulb, fan, computer hard drive, or other device.
All of these devices convert electrical energy into another form of energy;
(e) (iv) A compact fluorescent light bulb, or CFL, requires less energy to emit the same amount of light as
a comparable incandescent light bulb.
10. (a)
one thousand (1000) watts
(b)
one million (1 000 000) watts
(c)
one billion (1 000 000 000) watts
11.
Sample answer: I should tell my friend to have the cord replaced because having a bare wire exposed is
dangerous. If someone were to touch the bare wire while the cord was plugged in, he could receive an
electric shock. Also, an electric spark from the exposed wire could start a fire.
12.
These methods use energy (derived from running water, steam, or wind) to turn the blades of a turbine,
which rotates a coil of wire inside a generator, producing electricity.
13. (a) % efficiency 5
Energyin 5
(b)
14.
Energyout
Energyin
3 100 %
Energyout
1 % efficiency 4 100 2
It is less efficient.
5
900 J
5 1406 25 J 5 1406 J
0.64
900
5 60 % efficient; 60 % < 64 %
1500
cost to operate 5 power used in kilowatts 3 time 3 cost of electricity
time 5 cost to operate 4 (power used in kilowatts 3 cost of electricity)
5 75¢ 4 (4.4 kW 3 5.6 ¢/kW?h) 5 3 hours
15.
Sample answer: Are your appliances energy efficient? If not, you may be losing out. Over time, a cheaper,
less energy-efficient appliance may cost you more to operate than a comparable energy-efficient model.
Energy efficiency is not just about saving money, though. By using less energy, an energy-efficient
appliance will save energy resources and help protect the environment by consuming less energy than a less
energy-efficient model.
16.
Sample answer: During the past week, I turned off the lights when leaving a room; turned on a fan instead
of the air conditioner; opened the refrigerator for only short periods of time; placed the computer on
standby when not in use; and hung some clothes on a clothesline to dry instead of using the dryer.
17.
No. The speaker must use more than 30 W to produce 30 W of power. All electrical devices use more
power than they produce because no device is 100 % efficient.
18.
Sample answer:
Example
19.
How the electrons
move
Length of electron
flow
Static
electricity
lightning
electrons gather in one
place and are eventually
discharged in an
uncontrolled way
electrons flow for very
brief periods
Current
electricity
electricity
powering a laptop
computer
electrons flow steadily
through a conductor
electrons flow for as long
as the device is supplied
with electrical energy
Electricity will not flow out of a wall outlet unless something that can carry the electricity is plugged into
the outlet and the circuit is completed. Something that carries electricity from one place to another is
called a conductor. Most metals are conductors of electricity, which is why the prongs of a plug and the
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wires in a cord are made of metal. If nothing is plugged into an outlet, the electric circuit is not complete
and electricity will not flow.
20. (a)
Sample answer: I have been told that wind farms make a lot of noise. I like to sleep with my bedroom
windows open, and I do not want to keep my windows shut to try to reduce the noise level. Also,
the tall wind turbines would interrupt the scenic view that I now enjoy. In addition, I know that a
wind farm is very expensive to build. I cannot afford and do not want to pay higher taxes to build
something to which I am opposed.
(b)
Sample answer: Someone may argue that the benefits of wind generation outweigh the drawbacks.
For example, a wind farm would result in less air pollution in the area than a power plant relying on
traditional energy sources. Also, he or she may point out that advances in wind technology have made
wind farms less noisy.
21. (a)
(b)
22.
(b)
850
Sample answer: Manufacturers could provide a free service to pick up old appliances and take them to
a site where the metal and other parts are recycled.
Sample answer: I think tidal generation of electrical energy would be a good choice for my community.
I live along the coast where the change in water level from high tide to low tide is large enough to harness
it for energy production. Turning tidal energy into electrical energy results in no pollution. Also, tidal
energy is a renewable resource because the tidal cycle usually occurs twice a day and does not stop.
23. (a)
24.
Sample answer: If the appliance still works, the consumer could donate it to a local organization that
provides help for people in need. If it does not work and cannot be repaired the appliance should be
recycled.
Sample answer: Land that could be used to grow food crops might be used to grow biofuel crops
instead, if a greater profit can be made. Therefore, production of food crops may decline as more
agricultural land is devoted to producing crops used as biofuel.
Sample answer: I think the price of food and the price of land would go up. I also think growing
biofuel crops instead of food crops would affect people in poorer countries more, because richer
countries can afford to import food they cannot grow themselves. Poorer countries cannot afford to
import food to make up for what they cannot grow, so people there would have less food available
to them.
Light bulbs are generally not very efficient. Many light bulbs convert most of their input energy into
thermal energy, and they can become very hot. If a hot light bulb comes in contact with or is placed close
to a flammable material, it could start a fire.
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