Download Name: Gravitational, Electric and Magnetic Fields

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K/U-
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C-
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A-
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T/I-
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Gravitational, Electric and Magnetic Fields - SPH4U1
Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
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1. Which statement best describes differences and similarities among electrostatic force, magnetic force, and
gravitational force?
a. All three follow the inverse square law, with electrostatic force and magnetic force
needing two poles or charges.
b. Magnetic force and gravitational force follow the inverse square law, with electrostatic
force needing two opposite charges.
c. All three require opposite poles or charges, but only gravitational force follows the inverse
square law.
d. Electrostatic force and gravitational force have associated fields, but magnetic force does
not.
e. Gravitational force is stronger than electrostatic force, and both follow the inverse square
law.
2. To investigate electric field intensity, a test charge must be used. What charge is required?
a. 0 C
b. 1.0 C
c. 1.6  1019 C
d. same as the charge for an electron (but could be positive)
e. none of the above
3. Which statement best explains why the gravitational field intensity changes from position to position on
Earth’s surface.
a. The Moon and the Sun affect Earth’s gravity.
b. Earth is not a perfect sphere, and the distance to the centre varies.
c. Earth is not a perfect sphere, the distance to the centre varies, and there is an inertial effect
because of Earth’s rotation.
d. Some surface features on Earth are denser than others and cause a greater effect on gravity
in the local area.
e. Earth cannot be considered a true point source for gravity.
4. Carrie and Anne use different-sized test charges in an unchanging electric field. Carrie uses twice the charge
of Anne. What does Anne find?
a. the same field as Carrie
b. a stronger field than Carrie
c. a weaker field than Carrie
d. a difference determined by the mass of the test charges
e. a difference determined by the charge of the test charges
5. Why is a very small amount of charge used for a test charge?
a. because it moves easily
b. because it is easy to calculate
c. so it will not influence the electric field intensity too much
d. so it can only be influenced by one other charge object
e. so it is not affected by the inverse square law
6. A charged particle is placed at rest in a magnetic field. What will the particle do?
a. accelerate
b. stay at rest
c. move at a constant speed
d. come to rest between magnetic lines of force
e. none of the above
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7. What is the convention for the direction of a magnetic field?
a. directed out from the North Pole
b. directed out from the South Pole
c. determined by the direction of the electric field
d. determined by the number of atoms lined up magnetically
e. determined by the position of the monopole
____ 8. Which statement describes how a positively charged particle, placed between two oppositely charged plates,
will behave?
a. It will remain stationary.
b. It will move toward the negative plate at a constant speed.
c. It will accelerate toward the negative plate.
d. It will move parallel to the plates.
e. It will move against the direction of the electric field.
____ 9. Which property is observed when a beam of charged particles is fired into a magnetic field?
a. If the beam of charged particles is parallel to the magnetic field, no deflection will occur.
b. The maximum deflection happens when the beam is perpendicular to the magnetic field.
c. The magnitude of the magnetic deflecting force is directly proportional to the magnitude
of the charge on each particle.
d. The magnetic deflecting force is always perpendicular to the direction of travel of the
charge and to the magnetic field.
e. all of the above
____ 10. Electrons are moving south, through a uniform magnetic field that is also directed south. What happens to the
electrons?
a. They speed up.
b. They turn to the right.
c. They slow down.
d. They are not be affected by the field.
e. They turn to the left.
Short Answer
For the following questions, write the most appropriate answer in the space provided.
11. Compare the conventions used for directions of field lines in gravitational, magnetic, and electric fields. (3 M)
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12. Why can magnetic field intensity not be described/tested in the same way as gravitational or electrostatic field
intensity? (3 M)
13. Why are magnetic fields and electric fields used in particle accelerators? (2 M)
14. The following diagram shows a field around a single charged particle with an invisible companion. Add the
invisible companion and its field. (2 M)
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Problem Solving
For the following questions, write the answer in the space provided. If the question requires mathematical
calculations, show all of your work.
15. Each side of a vertical right-angled isosceles triangle measures 1.87 cm. Three charged objects are placed at
the vertices (corners) of the triangle. Each of the two objects at the vertices of the base has a charge of +5.00
C. The object at the top vertex (right angle) of the triangle has a charge of +4.74 C. What is the net force
on theobject at the top vertex? (4 M)
16. Two objects, with charges of 3.9 C and +5.3 C, are placed 21.0 cm apart. What is the electrostatic force
between these objects? (3 M)
17. A wire, 20.0 cm long, is placed in a uniform magnetic field at an angle of 45 to the field. The field strength is
5.0 T. What is the force on the wire if it is carrying a current of 3.0 A? (3 M)
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18. A wire is carrying a current of 3.27 A through a uniform magnetic field of 1.73 T. The force on the wire is
6.314 N. What is the length of the wire? (3 M)
19. Find the electric field intensity around a positively charged particle at point X in the following diagram. (5 M)
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Critical Thinking/Applications
For the following questions, write the answer in the space provided. Use complete sentences in your answer.
If the question requires mathematical calculations, show all of your work. Write a final statement that gives
your solution.
20. The strength of the electric field between two parallel charged plates is uniform, whereas the field around a
single source falls off with the square of the distance. Explain how this can be illustrated by each of the
following situations? (Use the necessary diagrams in your answer)
a) the shape of the field lines for a single positive source, compared with the shape of the field lines of the
plates. (3 M)
b) the velocity of a positive test charge placed next to the single source, compared with the velocity of a
positive test charge placed next to the positive plate. (3 M)
21. Some fish produce a dipole electric field to detect other organisms, such as predators and prey in their
environment. From what you know about an electric field, how does this work? (2 M)
22. At what angle must a charged particle move, with respect to a magnetic field, for the field to have the
maximum force on it? Explain using the formula as a proof. (2 M)
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Name:_____________________________
Unit Test 3
Answer Section
MULTIPLE CHOICE
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
A
E
B
A
C
A
A
C
E
D
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
easy
average
difficult
average
easy
easy
easy
average
average
easy
REF:
REF:
REF:
REF:
REF:
REF:
REF:
REF:
REF:
REF:
K/U
K/U
K/U
K/U
K/U
K/U
K/U
K/U
K/U
K/U
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
EG 1.01, EG 1.02, EG 1.04
EG 1.01, EG 1.06
EG 1.01, EG 1.02, EG 1.03
EG 1.01
EG 1.01, EG 1.04
EG 1.01, EG 1.04, EG 1.08
EG 1.01, EG 1.04
EG 1.01
EG 1.01, EG 1.08
EG 1.06
SHORT ANSWER
11. ANS:
Magnetic and electric field lines emanate from a point (north and positive, respectively) and terminate at a
point (south and negative, respectively). Gravitational field lines terminate at a mass but do not emanate from
a source point.
DIF: easy
REF: K/U, C
LOC: EG 1.01, EG 1.04, EG 1.06
12. ANS:
A source particle (such as a charged particle or a particle with mass) for magnetism (magnetic monopole) has
not been found.
DIF:
easy
REF: K/U
LOC: EG 1.01, EG 1.04, EG 1.06
13. ANS:
Electric fields are used to accelerate the charged particles. Electric fields and magnetic fields are both used to
guide and direct the charged particles.
DIF:
easy
REF: K/U
LOC: EG 1.07
14. ANS:
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15. ANS:
Vector Sum =
= 8.50  102 N[Up]
DIF: average
16. ANS:
DIF:
REF: K/U, I
LOC: EG 1.01, EG 1.03, EG 1.04, EG 1.06
easy
REF: K/U, I
LOC: EG 1.01, EG 1.03, EG 1.04, EG 1.06
average
REF: K/U
LOC: EG 1.05, EG 1.06, SPHU V.11
average
REF: K/U
LOC: EG 1.01, EG 1.06
17. ANS:
DIF:
18. ANS:
DIF:
8
Name:_____________________________
19. ANS:
Assume a positive charge.
1.83  103 1.467  103 cos 23.4
 2.693  103 N/C
0 1.467  103 sin 23.41.33  103
 5.317  103 N/C
Direction:
Fnet  5.96  103 N/C [up 24.3 left]
DIF:
average
REF: I
LOC: EG 1.01, EG 1.06
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PROBLEM
20. ANS:
a) The field lines around the single source move radially outward such that the distance between them
increases, indicating decreasing field strength. The field lines between the plates are parallel, indicating
constant strength.
b) A test charge that is placed next to a single source will move outward with a decreasing acceleration as the
electric force on it decreases with distance. A test charge that is placed next to the positive plate will move
to the negative plate with constant acceleration since the force on it is constant.
DIF: average
REF: K/U, MC
LOC: EG 3.01, EG 3.02
21. ANS:
Charges affect the field that is produced by the fish. Since the nervous systems of other organisms constitute
moving charges, they affect the electric field. The resulting change is detectable. The amount of the change
could indicate the size of the other organism, and this could help the fish distinguish predator from prey.
DIF: average
22. ANS:
90
DIF:
easy
REF: K/U, C, MC
LOC: EG 1.01, EG 1.04, EG 3.01
REF: K/U
LOC: EG 1.08
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