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