Download Unit 3 Review

Unit 3 Review
____
1. Which of the following diagrams best illustrates the electric field in the area around two identical charges?
a.
d.
b.
e.
c.
2. The electric field 0.50 m from a small sphere with a negative charge of 2.4 10 8 C is
a. 8.6 102 N/C [inward]
d. 4.3 102 N/C [inward]
2
b. 4.3 10 N/C [outward]
e. 7.8 1012 N/C [outward]
8
c. 9.6 10 N/C [outward]
____ 3. The potential difference between two parallel plates is 1.7 104 V. To move a small charge from one plate to
another opposing the electric field requires 0.56 J of work. The magnitude of the charge is
a. 3.0 104 C
d. 3.3 10 5 C
3
b. 9.5 10 C
e. 4.8 10 15 C
c. 1.5 10 15 C
____ 4. A electron of charge 1.6 10 19 C is moving east with a speed of 8.2 105 m/s, as it enters a magnetic field
of 1.5 T directed downward. The magnitude and direction of the magnetic force acting on the proton is
a. 8.7 10 14 N [S]
d. 2.0 10 13 N [S]
b. 2.9 10 25 N [N]
e. 2.9 10 25 N [S]
13
c. 2.0 10 N [N]
____ 5. A 50.0-cm straight conductor carries a current of 10.0 A through a uniform 0.70-T magnetic field. When the
magnitude of the force on the conductor is 0.5 N, the angle between the current and the magnetic field is
a. 8.2°
d. 35°
b. 0.036°
e. 0.14°
c. 2.1°
____ 6. What is the magnitude of the magnetic field 4.5 cm from a long, straight conductor carrying a current of 6.3
A?
a. 8.9 10 6 T
d. 2.8 101 T
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b. 2.9 10 T
e. 2.8 10 1 T
5
c. 2.8 10 T
____ 7. Which factor does NOT affect the strength of an electromagnet?
a. direction of the windings
d. number of turns in the coil
b. resistance of the coil
e. permeability of the core
c. diameter of the coil
Problems
____
8. The electrostatic force between two point charges is
. If the distance between them is tripled, the
charge of one of the points triples and the charge of the other point halves. What will be the force between
them?
9. Draw an electric field in the region around two positive point charges close to one another.
10. Calculate the electric field 1.0 m from a small sphere with a positive charge of 3.2
10 3 C.
11. Calculate the electric field 0.8 m from a small sphere with a negative charge of 4.7
10 2 C.
12. A proton with a charge of 1.60
10
19
C is shot from plate B toward plate A with a speed of 1.5
106 m/s.
(
d = 0.0030 m)
(a) What is the electric potential between the plates?
(b) What will the speed of the proton be just before it hits plate A?
13. In a Millikan-type experiment, two horizontal parallel plates are 1.0 cm apart. A sphere of mass 2.2 10 13 kg
remains stationary when the potential difference between the plates is 350 V with the upper plate negative.
(a) Is the sphere positively or negatively charged? Explain.
(b) Calculate the magnitude of charge on the sphere.
(c) How much excess or deficit of electrons does the sphere have?
14. In a Millikan-type experiment, two horizontal parallel plates are 3.5 cm apart. A sphere of mass 4.2 10 17 kg
remains stationary when the potential difference between the plates is 5.00 V with the upper plate positive.
(a) Is the sphere positively or negatively charged? Explain.
(b) Calculate the magnitude of charge on the sphere.
(c) How much excess or deficit of electrons does the sphere have?
15. Calculate 1.92
10
18
C as a multiple of the elementary charge.
16. An electron accelerates from rest through an electric field and into a magnetic field as shown in the diagram
below. The plates have a potential difference of 85 V and the magnetic field has a magnitude of 0.75 T.
(Remember: me = 9.1 10 31 kg and e = 1.6 10 19 C.)
(a) Calculate the initial speed of the electron upon entering the magnetic field.
(b) Calculate the magnitude and direction of the magnetic force on the electron.
(c) Calculate the radius of the electron s circular path.
17. Calculate the potential difference needed to accelerate sulfur-32 ions with a charge magnitude of 3.2 10 19 C
and a mass of 5.35 10 26 kg into a mass spectrometer, with a uniform 3.7-T magnetic field. The radius of the
curved path is 1.15 cm.
18. A straight conductor carries a current of 20.0 A through a uniform 0.950-T magnetic field. The magnitude of
the force on the conductor is 15.0 N and the angle between the current and the magnetic field is 55.0°.
Calculate the length of the conductor.
19. The magnitude of the magnetic field 0.50 m from a long, straight conductor is 2.73
current flowing through the wire.
10 3 T. Determine the
Unit 3 Review
Answer Section
MULTIPLE CHOICE
1.
2.
3.
4.
5.
6.
7.
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
A
A
D
D
A
C
A
REF:
REF:
REF:
REF:
REF:
REF:
REF:
K/U
C
C
C
C
C
K/U
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
7.3
7.3
7.6
8.2
8.3
8.4
8.5
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
PROBLEM
8. ANS:
Since
The force between the two charges will be 7.8
REF: C
9. ANS:
REF: C
10. ANS:
q = 3.2 10 3 C
10
6
N.
OBJ: 7.2
LOC: EG1.03
OBJ: 7.3
LOC: EG1.06
EG1.04
EG1.06
EG1.05
EG1.08
EG1.08
EG2.02
EG1.01
r = 1.0 m
The electric field is 2.9
REF: C
11. ANS:
q = 4.7 10 2 C
r = 0.8 m
OBJ: 7.3
The electric field is 6.6
REF: C
12. ANS:
(a)
107 N/C [radially outward].
LOC: EG1.06
108 N/C [radially inward].
OBJ: 7.3
LOC: EG1.06
d = 0.0030 m
V=?
The electric potential between the plates is 30 V.
(b)
EK lost = Ep gained
The speed of the proton will be 1.5
REF: C
OBJ: 7.6
13. ANS:
r = 1.0 cm = 0.010 m
m = 2.2 10 13 kg
106 m/s.
LOC: EG1.05
q=?
N=?
(a)
The electric force must be up to balance the downward force of gravity. The upper plate is negative and the
bottom plate is positive. The sphere must be positively charged to be repelled by the bottom plate and
attracted to the upper plate.
(b)
and
The magnitude of charge on the sphere is 6.2
10
17
C.
(c)
The sphere has a deficit of 385 electrons since its charge is positive.
REF: C
OBJ: 7.5
14. ANS:
r = 3.5 cm = 0.035 m
m = 4.2 10 17 kg
LOC: EG1.06
q=?
N=?
(a)
The electric force must be up to balance the downward force of gravity. The upper plate is positive and the
bottom plate is negative. The sphere must be negatively charged to be repelled by the bottom plate and
attracted to the upper plate.
(b)
and
The magnitude of charge on the sphere is 2.9
10
18
C.
(c)
The sphere has an excess of 18 electrons since its charge is negative.
REF: C
15. ANS:
OBJ: 7.5
LOC: EG1.06
Therefore, the multiple of elementary charge is 12e.
REF: C
OBJ: 7.5
16. ANS:
V = 85 V
B = 0.75 T = 0.75 kg/C·s
me = 9.1 10 31 kg
v=?
FM = ?
r=?
LOC: EG1.06
(a)
The initial speed of the electron upon entering the magnetic field is 5.5
106 m/s.
(b)
The right-hand rule tells us the direction of the force is toward the top of the page.
The magnitude of the force is 6.6 10 13 N [toward the top of the page].
(c)
The radius of the circular path is 4.1
10 5 m.
REF: C
OBJ: 8.2
17. ANS:
q = 3.2 10 19 C
m = 5.35 10 26 kg
B = 3.7 T
r = 1.15 cm = 1.15 10 2 m
The potential difference needed is 5.4
REF: C
18. ANS:
I = 20.0 A
B = 0.950 T
F = 15.0 N
OBJ: 8.2
LOC: EG1.08
103 V.
LOC: EG1.08
The length of the conductor is 0.964 m.
REF: C
19. ANS:
r = 0.50 m
B = 2.73 10 3 T
I=?
OBJ: 8.3
LOC: EG1.08
The current flowing through the wire is 6.8
REF:
C
OBJ: 8.4
103 A.
LOC: EG2.02
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