CHAPTER
7
Self-quiz
K/U
Knowledge/Understanding
For each question, select the best answer from the four
alternatives.
1. The SI unit of electrostatic charge is the
(a) electron
(b) ion
(c) coulomb
(d) newton (7.1) K/U
2. A negatively charged plastic rod comes close to, but
does not touch, a neutral metal sphere. While the rod is
still close, someone momentarily touches the opposite
side of the sphere with her finger. The charge on the
metal sphere is
(a) negative
(b) positive
(c) neutral
(d) cannot be determined (7.1) K/U
3. When a positively charged metal sphere comes in
contact with an electrical ground,
(a) protons flow from the object into the ground
(b) electrons flow from the object into the ground
(c) protons flow from the ground into the object
(d) electrons flow from the ground into the object
(7.1) K/U
4. Two charged metal spheres, separated by 20 cm,
attract each other with a 12 N force. Determine the
resulting force when the charge on each sphere is
reduced by half. (7.2) T/I
(a) 3 N
(b) 6 N
(c) 24 N
(d) 48 N
5. Two plastic spheres are placed on a number line. Both
spheres have a negative charge of equal magnitude.
Determine the region where the net electric field is
zero. (7.2) K/U
(a) to right of the rightmost sphere
(b) to the left of the leftmost sphere
(c) in between the spheres on the number line
(d) below the spheres
6. The electric field at a distance of 1.0 m from a charged
sphere is 100 N/C. At what distance from the sphere
will the electric field be 50 N/C? (7.3) T/I
(a) 1.1 m
(b) 1.4 m
(c) 2.0 m
(d) 4.0 m
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8160_CH07_p346-375.indd 369
T/I
Thinking/Investigation
C
Communication
A
Application
7. How much kinetic energy is obtained by a 5 C charge
as it moves from a position of 12 V electric potential
to a position of 4 V? (7.4) T/I
(a) 20 J
(b) 30 J
(c) 40 J
(d) 60 J
8. A particle of dust obtains a charge of −4.8 3 10219 C.
Determine how many excess electrons the dust
obtained. (7.6) T/I
(a) 2
(b) 3
(c) 4
(d) 5
Indicate whether each statement is true or false. If you think
the statement is false, rewrite it to make it true.
9. Two identical balloons are each rubbed with a wool
cloth. When held close together, the balloons will
repel each other. (7.1) K/U
10. Electrons and protons are attracted to each other
because they have the same magnitude of electric
charge. (7.1) K/U
11. For large objects, such as moons and planets,
electrostatic forces are stronger than gravitational
forces. (7.2) K/U
12. Liquid crystal displays (LCDs) use electric fields
to display pictures and messages on cellphones.
(7.3) K/U
13. An electrostatic precipitator first imparts a negative
charge to a dust or a flue gas particle. Then the
precipitator captures that particle through
electrostatic attraction. (7.3) A
14. The amount of work done by the electric field in
moving a charged object from point A to point B
within the field does not depend on the path taken
between the points. (7.4) K/U
15. A negative electric charge is moved from infinity to
a point some distance from a positive charge. The
electric potential will increase. (7.5) K/U
16. Every subatomic particle detected so far by
researchers has an electric charge equal to a
positive or negative whole-number multiple of
the fundamental charge e. (7.6) K/U
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Chapter 7 Self-Quiz 369
4/27/12 10:31 AM