CHAPTER 24
1. Assume the current in the wire shown in
Figure 24-24 on page 576 of your
textbook goes in the opposite direction.
Copy the wire segment and sketch the
new magnetic field the current generated.
7. A 3.0-cm long wire lies perpendicular to
a magnetic field with a magnetic
induction of 0.40 T. Calculate the force
on the wire if the current in the wire is
5.0 A.
F 5 BIL 5 (0.40 T)(5.0 A)(0.030 m)
5 0.060 N
i
8. What is the force on a 3.5-m long wire
that is carrying a 12-A current if the wire
is perpendicular to Earth’s magnetic field?
F 5 BIL 5 (5.0 3 10–5 T)(12 A)(3.5 m)
5 2.1 3 10–3 N 5 2.1 mN
2. Assume the current shown in
Figure 24-25 on page 577 of your
textbook goes into the page instead of
out of the page. Copy the figure with the
new current and sketch the magnetic
field.
9. A wire, 0.50 m long, is put into a
uniform magnetic field. The force
exerted upon the wire when the current
in the wire is 20 A is 3.0 N. What is the
magnetic induction of the field acting
upon the wire?
F 5 BIL, so
3. What happens to the strength of a
magnetic field around a wire if the
current in the wire is doubled?
It doubles, because magnetic field
strength is proportional to current.
The direction of the magnetic field is
also reversed.
5. What is the direction of the force on a
current-carrying wire in a magnetic field
if the current is toward the left on a page
and the magnetic field is down the page?
out of the page
6. A 0.25 m long wire is carrying a 1.25 A
current while the wire is perpendicular to
a 0.35-T magnetic field. What is the force
on the wire?
F 5 BIL, so
F
125 3 10–3 N
I 5 }} 5 }}} 5 4.2 A
BL
(0.085 T)(0.35 m)
11. A galvanometer has a full-scale defection
when the current is 50.0 µA. If the
galvanometer has a resistance of 1.0 kΩ,
what should the resistance of the
multiplier resistor be to make a voltmeter
with a full-scale deflection of 30.0 V?
V 5 IR, so
V
30.0 V
R 5 }} 5 }}
I
50.0 3 10–6 A
5 6.00 3 105 Ω
5 6.00 3 102 kΩ
RT 5 Rg 1 Rm , so
Rm 5 RT 2 Rg 5 600 kΩ 2 1.0 kΩ
5 599 kΩ
F 5 BIL 5 (0.35 T)(1.25 A)(0.25 m)
5 0.11 N
108
Supplemental Problems Manual
Physics: Principles and Problems
Copyright © by Glencoe/McGraw-Hill
4. What happens to the magnetic field
inside the coil of Figure 24–26 on page
577 of your textbook if the current shown
was reversed?
F
3N
B 5 }} 5 }} 5 0.30 T
IL
(20 A)(0.50 m)
10. What is the size of the current in a 35-cm
long wire that is perpendicular to a
magnetic field of 0.085 T if the force on
the wire is 125 mN?
Chapter 24 (continued)
12. A charged particle is moving to the right
in a magnetic field whose direction is up
the page. Show by diagram the direction
of the force exerted by the magnetic field
upon the particle if the particle is a
positive proton.
out of the page
B
F
The right-hand rule gives a direction
out of the page, but the force on an
electron is in the opposite direction,
into the page. So the force is
9.6 3 10–16 N into the page.
15. The electrons in a beam in a cathode ray
tube are moving horizontally at
5.0 3 107 m/s and pass through a vertical
magnetic field of 3.5 3 10–3 T. What size
force acts on each of the electrons in the
beam?
F 5 Bqv
5 (3.5 3 10–3 T)(1.60 3 10–19 C)
V
13. An electron beam moving horizontally
away from you is deflected toward the
right after passing through a certain
region of space that contains a constant
magnetic field. What is the direction of
the magnetic field?
Copyright © by Glencoe/McGraw-Hill
An electron beam moving away from
you is the same as a positive beam
moving toward you. The magnetic
field is either up or down the page if
the force is to the right. The righthand rule shows the magnetic field
must be down the page.
3 (5.0 3 107 m/s)
5 2.8 3 10–14 N
16. An ion of oxygen having 2 elementary
negative electric charges is moving at
right angles to a uniform magnetic field
for which B 5 0.30 T. If its velocity is
2.0 3 107 m/s, what force is acting on the
ion?
F 5 Bqv
5 (0.30 T)(2)(1.60 3 10–19 C)
3 (2.0 3 107 m/s)
5 1.9 3 10–12 N
14. A beam of electrons moving left at
3.0 3 107 m/s passes at right angles to a
uniform magnetic field that is down and
in which the magnetic induction is
2.0 3 10–4 T. What force acts upon each
electron in the beam?
F 5 Bqv
5 (2.0 3 10–4 T)(1.60 3 10–19 C)
3 (3.0 3 107 m/s)
5 9.6 3 10–16 N
Physics: Principles and Problems
Supplemental Problems Manual 109