Section 20.2
Electric Force
Practice Test
1.
Charging by induction occurs when __________.
a.
charge separation is used to charge an object without touching it
b.
a negatively-charged rod is touched to the knob of an electroscope
c.
electric charge causes the leaves of an electroscope to spread apart
d.
a neutral body is charged by touching it with a charged body
Hint
2.
How far apart are a proton and an electron if they exert a force of attraction of 4.5 N on each other?
a.
1.6 × 10
-19
m
b.
9.6 × 10
-15
m
c.
7.2 × 10
-15
m
d.
1.8 × 10
-5
m
Hint
3.
In Figure 20-11a, if
q
1
is 2.0 mC,
q
2
is 3.0 mC, and the separation between them is 2.5 m, what is the magnitude of the force between them?
a.
8600 N
b.
5400 N
c.
2.4 N
d.
220,000 N
Hint
4.
A positive and a negative charge, each of magnitude 2.7×10
-4
C, are separated by a distance of 10.0 cm. What is the force and direction of the force on each of the particles?
a.
6.6×10
4
N, repulsive
b.
- 6.6×10
4
N, attractive
c.
6.6×10
4
N, attractive
d.
6.6×10
2
N, repulsive
Hint
5.
If you increase the distance between two charges, what happens to the force?
a.
It increases.
b.
It stays the same.
c.
It decreases.
d.
It vanishes.
Hint
6.
An electron's charge is ________ in magnitude and _________ in sign from a proton's charge.
a.
unequal; same
b.
unequal; opposite
c.
equal; opposite
d.
equal; same
Hint
7.
Coulomb's law states that __________.
a.
the magnitude of the force between two charges is proportional to the magnitude of the charges and inversely proportional to the square of the distance between them
b.
the magnitude of the force between two charges is inversely proportional to the magnitude of the charges and proportional to the square of the distance between them
c.
the direction of the magnetic field in a wire is perpendicular to the flow of electric current in the wire
d.
the ratio of the potential difference to the current is constant
Hint
8.
In Figure 20-8, if the charge on the rod were positive, what effect, if any, would this have on the final result?
a.
The left sphere would still be positive and the right sphere would still be negative, but there would be less total charge on each.
b.
The left sphere would be negatively charged and the right sphere would be positively charged, with the same amount of charge as in the original picture c.
c.
It would have no effect.
d.
The left sphere would still be positive and the right sphere would still be negative, but there would be more total charge on each.
Hint
9.
How far apart are two electrons if they exert a force of repulsion of 2.5 N on each other?
a.
9.6 × 10
-15
m
b.
1.5 × 10
-14
m
c.
1.6 × 10
-19
m
d.
9.6 × 10
15
m
Hint
10.
A(n) __________ is a device used for detecting electrical charges.
a.
oscilloscope
b.
conducting sphere
c.
cathode-ray tube
d.
electroscope
Hint
11.
The SI standard unit of charge is the __________.
a.
coulomb
b.
volt
c.
joule
d.
ohm
Hint
12.
Three particles are placed in a line. The left particle has a charge of -47
m
C, the middle, +59
m
C, and the right, -91
m
C. The middle particle is 55 cm from each of the others. What is the net force on the middle particle?
a.
77 N, right
b.
77 N, left
c.
160 N, right
d.
83 N, right
Hint
13.
The rule for determining direction of force is __________.
a.
direction is determined by magnitude
b.
unlike charges repel, like charges attract
c.
like charges repel, unlike charges attract
d.
apply Coulomb's law
Hint
14.
A negative charge of -4.5×10
-3
C and a positive charge of 6.5×10
-3
C are separated by 0.50 m. What is the magnitude of the force between the two charges?
a.
2.2 × 10
6
N
b.
2.6 × 10
5
N
c.
1.1 × 10
6
N
d.
2.9 × 10
-5
N
Hint
15.
In Figure 20-11b, if
q
<
1
is 3.0 mC,
q
2
is -7.0 mC, and the separation between them is 3.0 m, what is the magnitude of the force between them?
a.
21,000 N
b.
43,000 N
c.
63,000 N
d.
7200 N
Hint
16.
A force of -8.2×10
4
N exists between a positive charge of 3.9×10
-5
C and a negative charge of -6.7×10
-5
C. What distance separates the charges?
a.
2.9×10
-4
m
b.
1.7×10
2
m
c.
1.4×10
2
m
d.
1.7×10
-2
m
Hint
17.
The magnitude of the charge of an electron is called the __________.
a.
frequency
b.
elementary charge
c.
negative charge
d.
secondary charge
Hint
18.
In Figure 20-8, if the charge on the rod were decreased, what effect, if any, would this have on the final result?
a.
The left sphere would still be positive and the right sphere would still be negative, but there would be more total charge on each.
b.
The left sphere would be negatively charged and the right sphere would be positively charged, with the same amount of charge as in the original picture c.
c.
It would have no effect.
d.
The left sphere would still be positive and the right sphere would still be negative, but there would be less total charge on each.
Hint
19.
A force of -7.7×10
3
N exists between a positive charge of 5.6×10
-4
C and a negative charge of -2.1×10
-4
C. What distance separates the charges?
a.
0.37 m
b.
1.4 m
c.
0.14 m
d.
3.7 m
Hint
20.
Two negatively-charged bodies, each charged with -7.4×10
-6
C, are 0.20 m from each other. What force acts on each particle and in what direction?
a.
2.5×10
3
N, attractive
b.
1.2×10
1
N, repulsive
c.
1.2×10
1
N, attractive
d.
3.0×10
5
N, repulsive
Hint
21.
__________ occurs when a neutral body is charged by touching it with a charged body.
a.
Charging by induction
b.
Static discharge
c.
Charging by conduction
d.
Charging by infusion
Hint
22.
If a charge were added to Figure 20-11b between the two charges already there, what direction would the net force on it be?
a.
To the right if charge is positive, to the left if it's negative.
b.
To the right, regardless of its sign
c.
This cannot be determined without knowing more about the location of the charge
d.
To the left if charge is positive, to the right if it's negative.
Hint
23.
Two identical positive charges exert a repulsive force of 5.8 × 10
-9
N when separated by a distance of 3.9 × 10
-10
m. What is the charge of each?
a.
1.0 × 10
37
C
b.
4.3 × 10
10
C
c.
3.1 × 10
-19
C
d.
-3.1 × 10
-19
C
Hint
