Understanding Vocabulary
Section 13.1
1. electric current
2. electrical symbols
3. switch
4. open circuit
5. closed circuit
6. resistance
Section 13.2
7. ampere
8. battery
9. voltage
10. volt
Section 13.3
11. ohm
12. Ohm’s law
13. resistance
14. potentiometer
15. conductor
Reviewing Concepts
Section 13.1
1. Electricity flows through a circuit of wires and water flows through a
circuit of pipes.
2. Natural circuits include: the nerves of the body create a circuit that
carries electrical signals throughout the body; a circuit is created as
lightning travels from clouds to Earth or Earth to clouds. Circuits
created by people include: the electrical service in your house; the
electrical supply system grid.
3. The symbols re a standard way of describing circuit connections so
that anyone trained in electrical circuits can understand the design
and operation of the circuit.
4. Answers are:
a.
b.
c.
d.
5. Resistors may represent many different loads in a circuit. Examples
include a toaster, a light bulb, a motor, a heater, or a speaker.
6. Sources of electrical energy include: batteries which may power mp3
players and flashlights; solar cells which may power calculators,
landscape lighting, satellites, and Mars rovers; and generating plants
which may power toasters and lamps.
7. No. When a circuit is open, current will not flow in the circuit.
8. A switch is a desirable way to open a circuit, but some other ways to
break a circuit are: breaks in the wire, or a broken filament in a light
bulb.
Section 13.2
9. positive; negative
10. Voltage is a measure of the electrical potential energy.
11. ampere; current; joule
12. A battery is like a water pump because the battery supplies electrical
potential energy to a circuit and a pump provides potential energy to
water.
13. Multimeters can measure both voltage and current for AC and DC
while ammeters measure only current and voltmeters only voltage
(potential difference).
14. To measure current, the current must pass through the meter.
Section 13.3
15. current
16. The amount of total resistance increases because you have more
resistive devices in the circuit.
17. The ohm. The omega, Ω.
18. If the resistance is doubled, the current will be reduced to ½. The
product of the current in a circuit and the resistance in the circuit is a
constant. A graph of current as a function of resistance in a circuit
produces a hyperbolic curve.
19. The current in a circuit is dependent upon the voltage. Doubling the
voltage in a circuit doubles the current.
20. voltage; resistance
21. Answers are:
a. The current will decrease and the bulb will not glow as brightly.
b. More current will flow in the circuit and bulb will glow more
brightly.
c. More current will flow in the circuit.
22. The resistance in a circuit will increase as the temperature of a
conductor increases. The bulb’s temperature increases when it is left
on for some time.
23. The resistance of dry skin is very high. It will not allow enough
current to flow to be harmful.
24. Conductors allow current to flow while insulators block the flow of
current.
25. Water reduces the resistance of the skin from 100,000 ohms to a
lower level which might allow dangerous current levels to flow
through your body.
26. Copper is a very good conductor. The covering material acts an
insulator to the wire from making contact with objects that should not
be exposed to the current and voltage of the conducting copper wire.
27. Semiconductors are materials that have less conducting ability than a
conductor but more ability than an insulator.
28. Answers are:
a. Conductor
b. Insulator
c. Insulator
d. Semiconductor
e. Conductor
f. Insulator
29. Fixed resistors have a resistance that cannot be changed. Variable
resistors can be adjusted to have a resistance within a certain range.
30. potentiometer
Solving Problems
Section 13.1
1.
Section 13.2
2. Answers are:
a. 1.5 V
b. 0 V
3. Diagram B
4. Since each AA battery supplies 1.5 volts of potential, combining four
batteries in series (stacking them on top of each other) would supply
6 volts.
Section 13.3
5. The current is reduced to 1/2; the current is reduced to 1/3.
6. The current is doubled; the current is tripled.
7. R = V/I = (120 V)/(10 A) = 12 Ω
8. I = V/R = (120 V)/(60 Ω) = 2 A
9. I = V/R = (6 V)/(3 Ω) = 2 A
10. Answers are:
a. V = IR = (1.5 A)(3 Ω) = 4.5 V
b. 3-1.5 volt cells
11. Answers are:
a. I = V/R = (6 V)/(2 Ω) = 3 A
b. I = V/R = (12 V)/(3 Ω) = 4 A
c. I = V/R = (9 V)/(2 Ω) = 4.5 A
12. R = V/I = (120 V)/(15 A) = 8 Ω
13. Each C battery supplies 1.5 volts of potential, for a total of 3 volts
with 2 batteries combined.
I = V/R = (3 V)/(6 Ω) = 0.5 A
Applying Your Knowledge
Section 13.1
1. Encourage your students to be creative in writing their paragraphs.
Electricity is basic and integral to modern life. Possible topics for
thinking about life without electricity could be home life, science
research, medicine, entertainment, sports, or school. This question is
very open to imaginative answers.
2. Ben Franklin was a prolific inventor, having invented bifocals, the
lightning rod, the Franklin iron furnace stove, an odometer, and a
glass armonica. Encourage your students to describe both the
invention and how these inventions were solutions to problems that
Ben Franklin saw in his life.
Section 13.2
3. Problems that can occur when electrical currents in the body don’t
work properly include: multiple sclerosis, diabetes, epilepsy, heart
disease, and many others. Students may find information by visiting
the web sites for the national societies for the promotion of research,
education, and support for many of these problems and diseases.
4. The web site www.howstuffworks.com contains an explanation of the
general nature of circuit breakers and fuses if nobody is available to
explain the operation of these devices in the home.
5. Answers will vary. Possible student answers include:
a. No, different types of household batteries can use different
electrochemical reactions, including carbon-zinc, alkaline, zinc
chloride, and zinc-silver oxide.
b. Rechargeable batteries can reverse the electrochemical reaction,
taking electrical energy and storing it as chemical energy.
c. Generally, lithium ion batteries.
6. In doing an experiment it is best to limit the number of experimental
variables to one so that its effect can be accurately measured. To
change the type of electrical device or the manner in which the
batteries are used introduces more variables, which is undesirable
when testing the effect of the type of battery.
Section 13.3
7. Answers will vary. Large appliances, like stoves, dishwashers or
refrigerators often will list voltage and current. Note that smaller
devices may list voltage and power ratings, but not current.
Example answers:
Dishwasher: 120 V; 6.2 A
R = V/I = (120 V)/(6.2 A) = 19.4 Ω
Refrigerator: 115 V; 11.6 A
R = V/I = (115 V)/(11.6 A) = 9.9 Ω