True/False
Indicate whether the
sentence or statement is true or false.
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1. |
The
electric force between two point charges is directly proportional to
the product of the charges and inversely proportional to the square
of the distance between them.
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2. |
If
the sum of all the electric forces on a charge is zero, the charge must
be at rest.
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3. |
Electric charges always move along a path given by electric field
lines.
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4. |
If
the electric field in a region of space is zero, the electric force
on any single charge placed in that region is also zero.
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5. |
When
a small positive test charge is moved toward another positive charge,
the test charge experiences an increasing electric force, an increasing
electric field, and an increase in electric potential energy. Further,
the charge finds itself moving into a region of higher electric potential.
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6. |
Negative charges move from regions of high electric potential to
regions of lower electric potential.
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7. |
An
oil droplet in a Millikan apparatus with uncharged plates falls at a
constant speed because it has a charge.
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8. |
The
laws of conservation of momentum and conservation of mechanical energy
determine the motion of interacting charged particles.
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9. |
A
negatively charged object that is fired directly away from a positively
charged object will cause the kinetic energy to increase and the potential
energy to decrease.
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10. |
Magnetic field lines never cross.
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11. |
Uniform electric, gravitational, and magnetic fields can change
the speeds of particles that are initially moving perpendicular to the
fields.
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12. |
A
charged particle moving parallel to an electric, gravitational, or magnetic
field experiences a force.
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13. |
Charges moving perpendicular to a uniform magnetic field experience
circular motion because the magnetic force is always perpendicular to
the velocity of the charge.
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14. |
Two
long, parallel, straight wires repel each other if their currents are
in the same direction.
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Multiple Choice
Identify
the letter of the choice that best completes the statement or answers
the question.
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15. |
The
force on a small, uniform conducting sphere of charge q1
a distance d from another sphere of charge q2
is +F. If the sphere of charge q1 is touched
with an identical neutral conducting sphere, which is moved far away
and then placed a distance  from
q2, the force on the sphere is
a. |
+F |
b. |
+2F |
c. |
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d. |
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e. |
none of these |
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16. |
Three
identical charges are placed on a line from left to right, with adjacent
charges separated by a distance d. The magnitude of the force
on a charge from its nearest neighbour is F. The net force on
each charge, from left to right, is
a. |
+2F, +2F, +2F |
b. |
 ,
0,  |
c. |
+2F, 0, +2F |
d. |
F,
0, F |
e. |
none of these |
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17. |
An
electron experiences a force of 1.6  10-16 N [left] from
an electric field. The electric field is
a. |
1.6
103 N/C |
b. |
1.0 
103 N/C [left] |
c. |
1.0 
103 N/C [right] |
d. |
1.0 N [right] |
e. |
none
of these |
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18. |
As
the distance between two charges increases, the electric potential energy
of the two-charge system
a. |
always
increases |
b. |
always decreases |
c. |
increases
if the charges have the same sign, decreases if they have opposite
signs |
d. |
increases
if the charges have opposite signs, decreases if they have the
same sign |
e. |
is
always negative |
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19. |
Two
oppositely charged parallel plates are separated by 12 mm. The uniform
electric field between the plates has a magnitude of 3.0 
103 N/C. An electron is ejected from the negative plate,
with an initial velocity of zero. The kinetic energy of the electron
when it has moved halfway to the positive plate is
a. |
2.9
10-18
J |
b. |
5.8
10-18
J |
c. |
1.4
10-18
J |
d. |
0
J |
e. |
none
of these |
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20. |
A
positive charge of mass 2m is initially at rest, directly to
the left of a negative charge of mass m, moving rightward with
speed v. When the negative charge has velocity 
[right], the velocity of the positive charge is
a. |
0 |
b. |
[right] |
c. |
[left] |
d. |
[right] |
e. |
[left] |
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21. |
Which
of the following statements is true about any type of field line:
a. |
They
never cross. |
b. |
They are always perpendicular to the surface of
the object producing the field. |
c. |
They point in the direction of motion. |
d. |
They
signify a force, experienced by a test particle of positive charge
q, whose magnitude equals the product of q and the
field magnitude. |
e. |
They never form closed loops. |
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22. |
Through
a narrow hole you view an apparatus in which a small charged sphere,
attached to a thin thread, hangs at rest at an angle of 10° to
the right of the vertical when there is no wind. From your observation,
you can infer that
a. |
the electric field points right |
b. |
the
electric field points left |
c. |
the electric field is zero |
d. |
the
net force on the sphere is zero |
e. |
the tension in the thread is smaller than the gravitational
force on the sphere |
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23. |
An
electron moves within a uniform magnetic field of 0.20 T, at a speed
of 5.0 
105 m/s. The magnetic force on the electron
a. |
is
1.6 
10-14
N |
b. |
is
1.6 
10-14
N [perpendicular to velocity] |
c. |
is 1.6 
10-14
N [perpendicular to magnetic field] |
d. |
is zero |
e. |
cannot be determined from the information |
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24. |
If
a straight length of wire with a current is immersed in a uniform magnetic
field, then the wire
a. |
experiences
no force if it is perpendicular to the field |
b. |
experiences some magnetic force, no matter what
its orientation in the field |
c. |
experiences no force if it is parallel to the field |
d. |
experiences no force if the current is alternating |
e. |
does not satisfy any of the above descriptions |
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25. |
An
electron passes into a magnetic field at 90°. Its consequent circular path has radius
r. If the speed of the electron were twice as great and the magnetic
field were twice as strong, the radius would be
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26. |
Particles
in a mass spectrograph emerge from a velocity selector into a uniform
magnetic field at 90°. If the radius of the circular path of particle
1 is larger than the radius for particle 2, then
a. |
particle
1 is of greater mass than particle 2 |
b. |
particle 1 has a smaller charge than particle 2 |
c. |
the
charge-to-mass ratio of particle 1 is smaller than the charge-to-mass
ratio of particle 2 |
d. |
the
charge-to-mass ratio of particle 1 is larger than the charge-to-mass
ratio of particle 2 |
e. |
particle
1 is moving faster than particle 2 |
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Completion
Complete each sentence
or statement.
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27. |
A(n)
_______ exists in a region of space when an appropriate object
experiences a force in that region.
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28. |
The
gravitational and electric forces are governed by a(n) _______
law with respect to the distance between the objects.
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29. |
If
a charged particle passes into a(n) _______ field perpendicular
to the field lines, the speed does not change.
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30. |
Electric
field lines are always _______ to a conductor in static equilibrium.
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31. |
A(n)
_______ cable is shielded from both electric and magnetic fields.
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32. |
The
area under the curve on an electric force-displacement graph represents
the change in _______ .
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33. |
To
analyze the motion of an elastic collision between two charged particles
we use conservation of _______ and _______ .
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34. |
When
a charged particle of mass m passes into either a uniform gravitational
field or an electric field perpendicular to the field lines, it follows
a(n) _______ path; however if it passes into a magnetic field
it follows a(n) _______ path.
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35. |
When
separating two charges of mass m the gravitational and electric
force _______ , the gravitational potential energy _______ , and the
electric potential energy _______ .
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