Section 26.1
Interactions of Electric and Magnetic Fields and Matter
Practice Test
1.
A mass spectrometer analyzes and gives data for a beam of doubly ionized atoms. The values are
q
= 3.20×10
-19
C,
B
= 4.0×10
-2
T,
r
= 0.220 m, and
V
= 45 V. Find the mass of one of these atoms.
a.
2.4×10
-16
kg
b.
8.7×10
-21
kg
c.
2.8×10
-25
kg
d.
4.3×10
-26
kg
Hint
2.
A stream of singly ionized atoms is not deflected as it passes through a 3.5×10[supserscript -3-T magnetic field perpendicular to a 2.8×10
2
-V/m electric field. What is the speed of the atoms as they pass through the crossed fields?
a.
4.7×10
2
m/s
b.
2.0×10
4
m/s
c.
8.0×10
4
m/s
d.
5.1×10
4
m/s
Hint
3.
The mass of an electron is determined by __________.
a.
weighing individual electrons on a balance inside a vacuum
b.
multiplying the strength of the electric field by the charge on the electron
c.
finding the charge-to-mass ratio and calculating the mass
d.
multiplying the velocity of the electron by the strength of the magnetic field
Hint
4.
A beam of singly ionized oxygen atoms is sent through a mass spectrometer. The values are
B
= 7.2×10
-2
T,
q
= 1.60×10
-19
C,
r
= 0.085 m, and
V
= 110 V. Find the mass of an oxygen atom.
a.
2.7×10
-26
kg
b.
8.9×10
-24
kg
c.
4.3×10
-26
kg
d.
2.7×10
-24
kg
Hint
5.
Protons passing perpendicular to and without deflection through a uniform magnetic field of 0.75 T are balanced by a 3.8×10
3
-N/C electric field. What is the speed of the moving protons?
a.
5.1×10
3
m/s
b.
2.0×10
-5
m/s
c.
7.5×10
3
m/s
d.
3.8×10
3
m/s
Hint
6.
Protons passing perpendicular to and without deflection through a uniform magnetic field of 0.54 T are balanced by a 5.4×10
3
-N/C electric field. What is the speed of the moving protons?
a.
9.0×10
3
m/s
b.
1.0×10
-4
m/s
c.
9.0×10
- 3
m/s
d.
1.0×10
4
m/s
Hint
7.
The __________ is used to determine the charge-to-mass ratio of gases.
a.
mass spectrometer
b.
antenna
c.
electron microscope
d.
cathode-ray tube
Hint
8.
Protons passing perpendicular to and without deflection through a uniform magnetic field of 0.97 T are balanced by a 8.1×10
2
-N/C electric field. What is the speed of the moving protons?
a.
8.4×10
2
m/s
b.
9.0×10
-3
m/s
c.
9.0×10
3
m/s
d.
1.2×10
2
m/s
Hint
9.
A stream of singly ionized atoms is not deflected as it passes through a 2.4×10
-3
-T magnetic field perpendicular to a 4.7×10
2
-V/m electric field. The atoms then move into a magnetic field of 0.31 T and follow a circular path of radius 0.175 m. What is the mass of each of these atoms?
a.
4.3×10
-26
kg
b.
4.3×10
-16
kg
c.
8.7×10
-21
kg
d.
2.4×10
-16
kg
Hint
10.
The charge-to-mass ratio of an electron in a Thomson tube is represented by the equation __________.
a.
q
/
m
=
v
/
Br
b.
m
/
q
=
v
/
Br
c.
q
/
m
=
Br
/
v
d.
q
/
m
=
Bqv
Hint
11.
An electron of mass 9.11×10
-31
kg moves through a cathode-ray tube with a speed of 2.6×10
6
m/s across and perpendicular to a magnetic field of 4.2×10
-2
T. The electric field is turned off. What is the radius of the circular path followed by the electron?
a.
4.6×10
3
m
b.
8.1×10
-1
m
c.
3.5×10
-4
m
d.
3.5×10
4
m
Hint
12.
In a spectrometer, a magnet causes the positive ions to be deflected according to their __________.
a.
charge
b.
electron configuration
c.
velocity
d.
mass
Hint
13.
Isotopes are atoms of the same element, which have different __________.
a.
numbers of protons
b.
masses
c.
chemical properties
d.
numbers of electrons
Hint
14.
A Thompson tube is configured like the one in Figure 26-1, such that the electrons sent through the tube with a particular velocity hit the center of the screen. If the velocity of the electrons were increased, where would they now hit the screen (from the electron's point of view)?
a.
to the right of center
b.
above the center
c.
below the center
d.
to the left of center
Hint
15.
A Thompson tube is configured like the one in Figure 26-1, such that the electrons sent through the tube hit the center of the screen. If the electric field were decreased, where would they now hit the screen (from the electron's point of view)?
a.
below the center
b.
to the left of center
c.
above the center
d.
to the right of center
Hint
16.
A proton moves at a speed of 7.9×10
3
m/s as it passes through and is perpendicular to a 0.45-T uniform magnetic field. Find the radius of the circular path.
a.
5.6×10
-7
m
b.
3.4×10
-3
m
c.
1.0×10
-4
m/s
d.
1.8×10
-4
m
Hint
17.
A Thompson tube is configured like the one in Figure 26-1, such that the electrons sent through the tube with a particular velocity hit the center of the screen. If the velocity of the electrons were decreased, where would they now hit the screen (from the electron's point of view)?
a.
below the center
b.
to the left of center
c.
to the right of center
d.
above the center
Hint
18.
A proton moves at a speed of 4.9×10
4
m/s as it passes through and is perpendicular to a 0.50-T uniform magnetic field. Find the radius of the circular path.
a.
1.0×10
-3
m
b.
8.2×10
-3
m
c.
5.6×10
-7
m
d.
5.0×10
1
m
Hint
19.
A proton moves at a speed of 7.9×10
3
m/s as it passes through and is perpendicular to a 0.60-T uniform magnetic field. Find the radius of the circular path.
a.
3.4×10
-3
m
b.
1.0×10
-3
m
c.
1.8×10
-4
m
d.
1.4×10
-4
m
Hint
20.
A Thompson tube is configured like the one in Figure 26-1, such that the electrons sent through the tube hit the center of the screen. If the magnetic field were increased, where would they now hit the screen (from the electron's point of view)?
a.
to the left of center
b.
below the center
c.
to the right of center
d.
above the center
Hint
21.
If Thomson's experiment depicted in Figure 26-1 were done with a proton, how would the magnitude of the
q/m
ratio obtained compare with that for an electron?
a.
It would be less.
b.
It would depend on the velocity of the proton.
c.
It would be more.
d.
It would be the same.
Hint
22.
Electrons move through and are perpendicular to a 4.0×10
- 2
-T uniform magnetic field balanced by a 7.0×10
3
-N/C electric field. What is the speed of the electrons?
a.
5.0×10
4
m/s
b.
3.0×10
5
m/s
c.
1.8×10
5
m/s
d.
5.7×10
- 7
m/s
Hint
