Download Electrostatics Practice Test

Electrostatics Practice Test
Multiple Choice
Identify the choice that best completes the statement or answers the question.
____
1. A repelling force occurs between two charged objects when the charges are of
a. unlike signs.
c. equal magnitude.
b. like signs.
d. unequal magnitude.
____
2. An attracting force occurs between two charged objects when the charges are of
a. unlike signs.
c. equal magnitude.
b. like signs.
d. unequal magnitude.
____
3. If a positively charged glass rod is used to charge a metal bar by induction, the charge on the bar
a. will be equal in magnitude to the charge on the glass rod.
b. must be negative.
c. must be positive.
d. will be greater in magnitude than the charge on the glass rod.
____
4. Charge is most easily transferred in
a. nonconductors.
b. conductors.
c.
d.
semiconductors.
insulators.
____
5. In the diagram shown above, the circles represent small balls that have electric charges. Ball 1 has a negative
charge, and ball 2 is repelled by ball 1. Next, you see that ball 2 repels ball 3 and that ball 3 attracts ball 4.
What is the electric charge on ball 4?
a. Ball 4 may have either a positive or negative charge.
b. Ball 4 has a negative charge.
c. Ball 4 has a positive charge.
d. It is not possible to determine the charge on ball 4.
____
6. The process of charging a conductor by bringing it near another charged object and then grounding the
conductor is called
a. contact charging.
c. polarization
b. induction.
d. neutralization.
____
7. The figure shown above demonstrates charging by
a. grounding.
c. polarization.
b. induction.
d. contact.
____
8. When a charged body is brought close to an uncharged body without touching it, a(n) ____ charge may result
on the uncharged body. When a charged body is brought into contact with an uncharged body and then is
removed, a(n) ____ charge may result on the uncharged body.
a. negative; positive
c. induced; residual
b. positive; negative
d. residual; induced
____
9. Which of the following is not true for both gravitational and electric forces?
a. The inverse square distance law applies.
b. Forces are proportional to physical properties.
c. Potential energy is a function of distance of separation.
d. Forces are either attractive or repulsive.
____ 10. Two point charges, initially 2 cm apart, are moved to a distance of 10 cm apart. By what factor does the
resulting electric force between them change?
a. 25
c.
b.
5
d.
____ 11. If the charge is tripled for two identical charges maintained at a constant separation, the electric force between
them will be changed by what factor?
a.
c. 9
b.
d.
18
____ 12. Which is the most correct statement regarding the drawing of electric field lines?
a. Electric field lines always connect from one charge to another.
b. Electric field lines always form closed loops.
c. Electric field lines can start on a charge of either polarity.
d. Electric field lines never cross each other.
____ 13. For a conductor that is in electrostatic equilibrium, any excess charge
a. flows to the ground.
b.
c.
d.
resides entirely on the conductor’s outer surface.
resides entirely on the conductor’s interior.
resides entirely in the center of the conductor.
____ 14. If an irregularly shaped conductor is in electrostatic equilibrium, charge accumulates
a. where the radius of curvature is smallest.
b. where the radius of curvature is largest.
c. evenly throughout the conductor.
d. in flat places.
____ 15. Resultant force on a charge is the ____ sum of the individual forces on that charge.
a. scalar
c. individual
b. vector
d. negative
Short Answer
16. An object that has a negative electric charge has an abundance of atomic particles called
____________________.
17. When a conductor is given a negative charge, the charge will move on the conductor until the repulsive forces
between the free electrons are in ____________________.
18. Materials, such as glass, in which electric charges do not move freely are called electrical
____________________.
19. A negatively charged rubber rod is brought near a neutral, conductive sphere that has no charge. As a result,
the part of the sphere closest to the rod becomes positively charged. Explain how this positive charge occurs.
20. How does the electric force between two charged objects change when the distance between the two objects is
doubled? Explain.
21. How are gravitational and electric force alike?
22. Any force between two objects that are not touching is called a(n) ____________________ force.
23. Draw the lines of force representing the electric field surrounding two objects that have equal magnitude
charges of opposite polarity.
24. Is the charge shown in the figure above positive or negative?
25. The diagram shown above represents a cross section of a copper rod that is electrostatically charged. Which
of the arrows—A, B, C, or D—best represents a field line in the rod’s electric field? Explain your choice.
1. Two positive charges of 1 mC and 10 mC are separated by a distance of 10 m. Find the direction and
the magnitude of electrostatic force between the charges. Describe the direction in terms of “the
charges attract each other,” or “the charges repel each other.”
2. A particle with a charge of +7.4 μC is separated from another charged particle with a charge of –3.6 μC
by a distance of 1.4 m. Find the direction and the magnitude of electrostatic force between the particles.
3. A +1.4 nC charge exerts a repulsive force of 20.0 mN on a second charge which is located a distance
of 2.2 m away from it. What is the magnitude and sign of the second charge?
4. Two spherical objects, whose centers are 8.0 cm apart, have equal negative charges and repel each
other with a force of 9.0 mN. What is the charge on each of them? How many extra electrons are on
each of them?
5. Two conducting spheres have net charges of +9.00 μC and -7.00 μC and attract each other with a force
of 4.00 mN. The spheres are brought in contact and then moved apart to the initial distance. What is the
new force between the spheres? Is this force attractive or repulsive?
6. Two negative charges of 2.5 μC and 9.0 μC are separated by a distance of 25 cm. Find the direction (in
terms of repulsive or attractive) and the magnitude of the electrostatic force between the charges.
7. Two charges of +2.6 μC and –5.4 μC experience an attractive force of 6.5 mN. What is the separation
between the charges?
8. What is the distance between two charges, +7.8 μC and +9.2 μC, if they exert a force of 4.5 mN on
each other?
9. A –4.2 μC charge exerts an attractive force of 1.8 mN on a second charge which is a distance of 2.4 m
away. What is the magnitude and sign of the second charge?
10. Two equal negative point charges repel each other with a force of 18.0 mN. What is the charge on each
object if the distance between them is 9.00 cm? How many extra electrons are on each object?
11. Two charged conducting spheres have net charges of +4.0 μC and -8.0 μC and attract each other with
a force of 16 mN. The spheres are brought into contact and then moved apart to the initial distance.
What is the new force between the spheres? Is this force attractive or repulsive?
12. What is the ratio of the electrostatic force to the gravitational force between two electrons?
13. A 0.140 kg metal ball is suspended at the end of a string and carries a positive charge of +10.0 nC. A
charged sphere with a negative charge of -25.0 μC is placed at 5.00 cm below the ball.
a. Draw a free-body diagram showing all the forces acting on the ball.
b. Find the tension force in the string.
c.
If the maximum tension force that the string can withstand is 3.00 N, how much charge must
be added to the ball in order to break the string?
d. What will be the tension force in the string if we changed the charge on the sphere from
-25.0 μC to +25.0 μC and leave the charge of the suspended ball at +10.0 nC?
14. Two identical balls (B and C) with a mass of 0.500 g are suspended from two strings as show above.
The balls carry equal charges, +10.0 nC each and are separated by a distance of 4.00 cm.
a. Draw a free-body diagram and show all forces applied on ball C.
b. Find the tension force in the string BC.
c.
Draw a free-body diagram and show all forces applied on ball B.
d. Find the tension force in string AB.
e. Answer questions a, b, c and d for the situation when the balls have equal but opposite
charges (charge on B is positive and charge on C is negative).
15. A positive charge Q1 = 2.6 μC is located at a point X1 = -3.0 m and a positive charge Q2 = 1.4 μC is located at a point X2 = +4.0 m.
a.
b.
c.
d.
Draw free body diagrams for the electric force acting on Q1 and Q2.
Find the magnitude of the electric force between Q1 and Q2.
Find the magnitude and direction of the electric force acting on Q1.
Find the magnitude and direction of the electric force acting on Q2.
16. **A positive charge Q1 = 7.4 μC is located at a point X1 = -2.0 m, a negative charge Q2 = -9.7 μC is located at a point X2 = 3.0 m and a positive charge Q3 = 2.1 μC is located at a point X3 = 9.0 m.
a.
b.
c.
d.
e.
f.
g.
Draw free body diagrams for the electric force acting on Q1, Q2 and Q3.
Find the magnitude of the force between Q1 and Q2.
Find the magnitude of the force between Q1 and Q3.
Find the magnitude of the force between Q2 and Q3.
Find the magnitude and direction of the net electric force on charge Q 1.
Find the magnitude and direction of the net electric force on charge Q2.
Find the magnitude and direction of the net electric force on charge Q 3.
Homework
17. **A negative charge Q1 = -25 μC is located at a point X1 = -2.0 m, a positive charge Q2 = 15 μC is located at a point X2 = 3.0 m and a positive charge Q3 = 18 μC is located at a point X3 = 9.0 m.
a.
b.
c.
d.
e.
f.
g.
Draw free body diagrams for the electric force acting on Q1, Q2 and Q3.
Find the magnitude of the force between Q1 and Q2.
Find the magnitude of the force between Q1 and Q3.
Find the magnitude of the force between Q2 and Q3.
Find the magnitude and direction of the net electric force on charge Q 1.
Find the magnitude and direction of the net electric force on charge Q 2.
Find the magnitude and direction of the net electric force on charge Q 3.
Chapter 17 Test
Answer Section
MULTIPLE CHOICE
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
B
A
B
B
C
B
C
C
D
D
C
D
B
A
B
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
I
I
II
I
II
I
I
I
I
II
II
II
I
I
I
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
16-1.1
16-1.1
16-1.1
16-1.2
16-1.1
16-1.3
16-1.3
16-1.3
16-2.2
16-2.2
16-2.2
16-3.2
16-3.3
16-3.3
16-2.3
SHORT ANSWER
16. ANS:
electrons
PTS: 1
17. ANS:
equilibrium
DIF: I
OBJ: 16-1.1
PTS: 1
18. ANS:
insulators
DIF: I
OBJ: 16-1.2
PTS: 1
DIF: I
OBJ: 16-1.2
19. ANS:
The negatively charged rod repels electrons from the part of the sphere nearest the rod. As a result, this part
becomes deficient in electrons, thus acquiring a positive charge.
PTS: 1
DIF: II
OBJ: 16-1.3
20. ANS:
The force decreases to one-fourth its previous value because the force is inversely proportional to the square
of the distance between the two objects.
PTS: 1
21. ANS:
DIF: IIIA
OBJ: 16-2.1
Both gravitational force and electric force are field forces. Both forces obey the inverse square law.
PTS: 1
22. ANS:
field
DIF: I
OBJ: 16-2.2
PTS: 1
23. ANS:
DIF: I
OBJ: 16-2.2
PTS: 1
24. ANS:
positive
DIF: I
OBJ: 16-3.2
PTS: 1
DIF: I
OBJ: 16-3.2
25. ANS:
Arrow B best represents a field line because the electric charge is all on the surface of a conductor, so the
field lines are always perpendicular to the surface at any point. No electric field exists inside the conductor.
PTS: 1
DIF: II
OBJ: 16-3.3