CHAPTER
13
Self-Quiz
SUGGESTED ANSWERS
1.
(c); Choice (c) best describes potential difference (voltage), which is the difference in electrical potential
energy per unit of charge measured at two points in a circuit. Choice (a) is incorrect because the rate of
flow of electrons is current. Choice (b) is incorrect because opposition to the flow of electrons is resistance.
Choice (d) is incorrect because potential difference is a measure of electrical potential energy, not the
number of electrons.
2.
(a); Choice (a) would have the most electrical resistance. As you increase the length of a wire, its internal
resistance increases because electrons have to travel through more material. Choice (b) is incorrect because
the thicker the wire, the lower the resistance would be. Choice (c) is incorrect because the colder the wire,
the lower the resistance would be. Choice (d) is incorrect because a copper wire would have relativey low
resistance as copper is a good conductor.
3.
(b); Choice (b) describes how electrical resistance is calculated using Ohm’s law. Choices (a), (c) and (d) are
V
incorrect because Ohm's law states that R 5
I
False. An ammeter does not count individual electrons. A true version of the statement could be: An
ammeter measures the rate of electron flow.
4.
5.
True. In a series circuit, the loads are connected so that there is only one path for the electrons to flow.
6.
False. The human body is sensitive to electric currents, and even small electric shocks can be dangerous. A
true version of the statement could be: Electric currents of 15 A are very dangerous to the human body.
7.
resistance; An ohmmeter is a device used to measure resistance.
8.
current; According to Ohm’s law potential difference varies directly with current.
9.
circuit diagram; A circuit diagram is a method of drawing an electric circuit using standard symbols.
10. (a)
(iv) A battery acts as a source of electrical energy in a circuit.
(b) (ii)
Connecting wire, often made of copper, provides a path for electric flow in a circuit.
(c) (iii)
A load, such as a lamp, converts electricity to another type of energy.
(d) (i)
A control device, such as a switch, opens and closes the circuit.
11.
Connecting the ammeter in series ensures that all of the electrons that flow through the load are also
flowing through the ammeter.
12.
In both situations, there is a break in the path for electrons to travel, so there is no electric current in
the circuit.
13.
Electrical signals from the brain control body systems. The brain coordinates the actions of the muscles
through electrical signals sent through the nervous system.
14.
Potential difference means the same thing as voltage, which is the difference in electric potential energy per
unit of charge measured at two points. The volt is the unit for voltage.
15. (a)
Because the voltage drop at the source is 12.0 V and there are two identical resistors, the voltage drop
across each resistor will be half of 12.0 V, or 6.0 V.
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(b)
V 5 IR
12.0 V 5 I/16.0 V
I 512 V/16.0 V
I 5 0.75 A
16.
V 5 IR
V 5 (5.0 A)(35.0 V)
5 175 V
17.
Electric current flows like water in a river. The stones in a river are like the resistors in a circuit.
The tributaries in a river are like the branches in the circuit.
18.
To measure potential difference you need to connect a voltmeter in parallel with a load. Because the two
leads of the meter are on either side of the load, the potential difference is said to be “across” the load.
In contrast, to measure current, you need to connect an ammeter in series with the load. This is to ensure
that all the current flows through the meter and also “through” the load.
19. (a)
In a parallel circuit, electrons can follow more than one path. In a series circuit, electrons follow only
one path.
(b)
ⴙ
ⴙ
ⴚ
ⴚ
parallel circuit
20.
series circuit
Sample answer: What are some of the safety regulations in your work? Do you wear any protective gear
when working with circuits? Have you ever suffered an injury on the job? What advice do you have for
homeowners who try to fix electrical problems without professional help?
21. (a)
(b)
If one light goes out, all of the lights will go out because there is an interruption in the circuit. This
interruption prevents the current from reaching the other loads.
Connecting the lights in a series circuit regulates the current that passes through each bulb. The
filament in each bulb does not need to withstand a high current.
22.
The voltage drop across each lamp would decrease because the potential energy from the source would be
divided among more loads. The brightness of each lamp would also decrease because brightness is related
to the amount of energy being converted at the load.
23.
She could decrease the length of the cable or increase its diameter. Both of these modifications would
decrease the resistance of the wire, which would help prevent overheating.
24. (a)
(b)
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All homes have an electrical panel with fuses or circuit breakers to ensure that circuits are not
overloaded with current. If too much current flows through the fuse or breaker, the fuse blows or the
breaker trips, acting like an open switch. Plugging in a hair dryer may cause a fuse to blow or breaker
to trip. If this happens, the other appliances in the circuit would also stop working.
Without a fuse panel, the current that flows through the circuits may become too large. This could
damage appliances and even start a fire.
Unit E: The Characteristics of Electricity
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