Download L`électricité et le magnétisme

Name: _______________________________________
Group: ______________
ST
Questions 1–5, 7–8, 10–18, 21–22, 24, A and D
Checkups and follow-ups
CHAPTER 5
Date: ___________
ANSWER KEY
Electricity and magnetism
Checkup
1 WHAT IS ELECTRICITY? (pp. 140–144)
1. Vanessa observes that an object is positively charged. Has it gained or lost electrons? Explain
your answer.
The object has lost electrons because a positive charge comes from an electron deficiency.
2. The five spheres opposite, identified A to E, carry
an electrical charge. If sphere A carries a positive
charge, what is the sign of the charges on each
of the other spheres? Explain your answer.
Spheres A and B are positively charged because
they repel each other. Sphere C is negatively
charged because it is attracted to sphere B.
Sphere D is negatively charged because it is
attracted to sphere A. Sphere E is negatively
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charged because it is repelled by sphere D.
3. During a storm, impressive bolts of lightning form jagged lines across the sky. The lightning is
caused by a brief but powerful electrical discharge. If the electrical discharge of a lightning bolt
is equal to 20 C, how many electrons were involved in the neutralization process?
20 C = ? electrons
1 C = 6.25  1018 electrons
20 C is equal to a charge of 1.25  1020 electrons.
4. After charging a piece of fabric, Jonathan calculates that it has lost 2 x 1015 electrons.
a) What is its charge in coulombs?
? C = 2  1015 electrons
1 C = 6.25  1018 electrons
Its charge is 0.000 32 C, or 3.2  10-4 C.
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CHAPTER 5
Electricity and magnetism
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Date: ___________
b) Is this charge positive or negative? Explain your answer.
The charge is positive because the fabric has lost electrons.
5. A copper rod and a plastic rod are electrically charged. In terms of attraction and repulsion, will
the charges behave in the same way in the two rods? Explain your answer.
No, because copper is a conductor and plastic is an insulator. In a conductor, charges spread out
uniformly over the surface of the object, while in an insulator, the charges do not move.

Question 6 is not intended for students in the ST program.
2 STATIC ELECTRICITY (pp. 145–149)
7. Are the following objects charged by friction, conduction or induction?
a) Carl brings a charged comb close to his hair without touching it, and his hair stands on end.
By induction
b) A certain number of charges are transferred from one body to another, resulting in two
bodies carrying like charges.
By conduction
8. To clean his copper trophy, Brad rubs it with a woollen cloth. What will be the charge on each
of these objects? Explain your answer.
The copper will accumulate a negative charge because it has a higher affinity for capturing electrons
than wool. The wool will have a positive charge because charges acquired by friction are of opposite
signs.

Question 9 is not intended for students in the ST program.
CHAPTER 5
Electricity and magnetism
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c) When we walk about, our bodies may accumulate an electrical charge.
By friction
Name: _______________________________________
Group: ______________
Date: ___________
3 DYNAMIC ELECTRICITY (pp. 150–163)
10. Do the following situations describe an example of static electricity or dynamic electricity?
Explain your answer.
a) an engine belt charging by friction
Static electricity, because charging by friction does not result in charges that move in a circuit.
b) an MP3 playing your favourite music
Dynamic electricity, because charges must flow for the MP3 player to work.
11. In which of the circuits below is the ammeter correctly connected? Explain your answer.
a)
b)
In circuit b) only. An ammeter is a device that must be connected in series and not in parallel as in a).
12. A hair dryer runs on an eight-ampere current. After five minutes’ use, what charge will have
been transferred to this appliance?
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Problem-solving steps
Application
1. Determine what you are looking for.
What charge will have been transferred to the hair
dryer after five minutes’ use?
2. Determine the different variables and
their respective values.
I =8A
∆t = 5 min = 300 s
q =?
3. Choose the appropriate formula.
q
∆t
q = I  ∆t
I=
4. Replace each variable by its value and
isolate the unknown variable.
q = 8 A  300 s
= 2400 C
5. Check your solution and answer the
problem question.
2400 C will have been transferred to the hair dryer
after five minutes’ use.
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CHAPTER 5
Electricity and magnetism
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Date: ___________
13. A charge of 5400 C flows through a circuit element in one hour. What is the intensity of the
electric current?
Problem-solving steps
Application
1. Determine what you are looking for.
What is the intensity of the current?
2. Determine the different variables and their I = ?
respective values.
∆t = 1 h = 3600 s
q = 5400 C
3. Choose the appropriate formula.
I=
4. Replace each variable by its value and
isolate the unknown variable.
5. Check your solution and answer the
problem question.
q
∆t
5400 C
3600 s
I = 1.5 A
I=
The current intensity is 1.5 A.
a)
b)
c)
d)
In c) and d) only. A voltmeter is a device that must be connected in parallel and not in series as in a)
and b).
CHAPTER 5
Electricity and magnetism
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14. In which of the circuits below is the voltmeter correctly connected? Explain your answer.
Name: _______________________________________
Group: ______________
Date: ___________
15. A wide variety of batteries are available on the market. What is the energy supplied by
a 1.5-V battery if 200 C of charge flow through an electrical appliance in 20 minutes?
Problem-solving steps
Application
1. Determine what you are looking for.
How much energy is supplied by the battery?
2. Determine the different variables and their
respective values.
V = 1.5 V
E =?
q = 200 C
3. Choose the appropriate formula.
E
q
E =Vq
4. Replace each variable by its value and
isolate the unknown variable.
E = 1.5 V  200 C
= 300 J
5. Check your solution and answer the
problem question.
The battery supplies 300 J of energy.
V=
16. To find the resistance of a heating element, Maria conducts an experiment. She discovers
that when the current intensity is 3.5 A, the potential difference at the terminals of the element
is 10 V. What is the resistance of the heating element?
V = RI
V
R =
I
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= 10 V
3.5 A
 2.86 
The resistance of the heating element is approximately 2.86 .
17. How much energy will an electrical appliance have consumed after 15 minutes’ use if the
current flowing through it has an intensity of 15 A and the potential difference is 120 V?
Problem-solving steps
Application
1. Determine what you are looking for.
How much energy was consumed by the
appliance?
2. Determine the different variables and their
respective values.
E
I
V
∆t
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=?
= 15 A
= 120 V
= 15 min = 900 s
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CHAPTER 5
Electricity and magnetism
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3. Choose the appropriate formulas.
E = Pe ∆t
Pe = VI
4. Replace each variable by its value and
isolate the unknown variable.
Pe = 120 V  15 A
= 1 800 W
E = 1 800 W  900 s
= 1 620 000 J
5. Check your solution and answer the
problem question.
The appliance consumed 1 620 000 J of energy.

a)
b)
Parallel
Series
c)
d)
Parallel
Series
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18. Which of the circuits below are connected in series, and which are connected in parallel?
Questions 19 and 20 are not intended for students in the ST program.
CHAPTER 5
Electricity and magnetism
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4 WHAT IS MAGNETISM? (pp. 163–167)
21. If the north pole of a magnet is moved toward the south pole of another magnet, will the north
pole be subjected to an attractive or a repulsive force? Explain your answer.
It will be subjected to an attractive force because opposite magnetic poles attract.
22. Which of the illustrations below is an accurate representation of the magnetic field of a bar
magnet? Explain your answer.
a)
b)
Only a) correctly represents the magnetic field of a bar magnet because the poles are shown to be at
the two ends.

Question 23 is not intended for students in the ST program.
5 ELECTROMAGNETISM (pp. 167–171)
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24. Which of the illustrations below is an accurate representation of the magnetic field of a live
wire? Explain your answer.
a)
b)
Only a) is correct. According to the right-hand rule, the thumb points in the conventional current
direction, and the fingers show the direction of the magnetic field lines.
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Electricity and magnetism
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
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Date: ___________
Questions 25 and 26 are not intended for students in the ST program.
REVIEW QUESTIONS

Questions B and C are not intended for students in the ST program.
A. Valerie charges an ebonite comb by rubbing it on her pants. She thus gives it a charge of
5  10–8 C. She then tries to lift up small pieces of paper with the charged comb.
a) If Valerie’s pants are made of wool, will the electrical
charge of the comb be positive or negative?
Explain your answer.
The comb will be negatively charged because ebonite has a
higher affinity for capturing electrons than wool.
b) How will the charges on the comb be distributed?
Explain your answer.
The charges will stay in one place because ebonite is an
insulator.
c) When Valerie moves the comb close to the pieces of paper, they become charged. Will the
electrical charges accumulating on the side of the paper closest to the comb be positive or
negative? Explain your answer.
They will be charges of the opposite sign to those on the comb (namely, positive). The presence of
d) When she moves the comb close to a metal ruler, Valerie sees a spark. She concludes that
the two objects have cancelled each other’s charge. If 5 x 10–8 C have been transferred
from one object to the other in 0.001 s, what was the intensity of the electrical discharge?
q
∆t
5  10−8 C
= 5  10−5 A
=
0.001 s
I=
The discharge had an intensity of 5  10−5 A.
CHAPTER 5
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opposite charges is what attracts the pieces of paper to the comb.
Name: _______________________________________
Group: ______________
Date: ___________
e) Air is an insulator with a resistance of 2 x 1010 Ω. What is the potential difference of the
electrical discharge between the comb and the metal ruler?
V = RI
= 2  1010 Ω  5  10−5 A = 1 000 000 V
The potential difference is 1 000 000 V.
D. Prepare your own summary of Chapter 5 by building a concept map.
See the Concept maps section in Guide B.
Follow-up
1. Briefly explain how a wind turbine can generate electricity using wind energy.
The wind turns the blades of the turbine, which transforms mechanical energy into electrical energy.
2. Do you think it would be a good idea to build wind turbines in your region? Explain your
answer, suggesting at least one advantage and one disadvantage.
Answers will vary. Examples:
Advantage: My region is an area of high winds.
Disadvantages: The wind is unpredictable.
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– In the city, there is not enough space to build turbines.
– In the country, the towers ruin the beauty of the landscape.
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CHAPTER 5
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