Physics P
Review
9
Unit 9 Review: Magnets and Electromagnetism
Magnets and Electromagnetism
1.
A 1.2–cm wire carrying a current of 0.8 A is
perpendicular to a 2.4–T magnetic field. What is
the magnitude of the force on the wire?
2.
A 24–cm length of wire carries a current and is
perpendicular to a 0.75–T magnetic field. If the
force on the wire is 1.8 N, what is the current in
the wire?
3.
A 0.5–cm length of wire carries a 26–A current to
your right in a 0.75–T magnetic field directed up.
a.
What is the direction of the force on the
wire?
b.
What is the magnitude of the force on the
wire?
4.
A 4.5–m length of wire carries a 2.1–A current
and is perpendicular to a magnetic field. If the
wire experiences a force of 3.8 N from the
magnetic field, what is the magnitude of the
magnetic field?
5.
A length of wire carrying a current of 2 A is
perpendicular to a 6.5–T magnetic field. What is
the length of the wire if it experiences a force of
2.99 N?
6.
An electron beam is perpendicular to a 0.02–T
magnetic field. What is the force experienced by
one electron if the beam has a velocity of
9.8 × 103 m/s?
7.
A moving proton experiences a force of
6.9 × 10-15 N when it travels at a right angle to a
1.35–T magnetic field. What is the velocity of the
proton?
8.
A doubly ionized particle travels upward with a
speed of 4.1 × 104 m/s through a magnetic field
with a strength of 1.5 T to the east. What is the
force experienced by the particle?
9.
An electron traveling 8.6 × 107 m/s at a right angle
to a magnetic field experiences a force of
2.9 × 10—11 N. What is the strength of the
magnetic field?
1
10.
A positively charged particle travels at a right
angle through a 3–T magnetic field with a velocity
of 4.5 × 105 m/s. If the par- ticle experiences a
force of 4.32 × 10–13 N as it travels through the
magnetic field, what is the charge on the particle?
11.
A screen of ten straight wires is laid horizontally
in an upward magnetic field of 24 T. Each wire
carries a current of 12 mA and is 50 cm long.
a.
What is the total force experienced by this
screen?
b.
If the force acts to the east what is the
direction of the current?
12.
A 15-cm length of wire is suspended horizontally
in a magnetic field of 8 T oriented at a right angle
to the wire in such a way that the force
experienced by this wire acts in the upward
direction.
a.
If the wire has a mass of 3 g and is able to
move freely, what current running through
this wire is necessary to lift the wire off the
ground?
b.
If this wire is turned 90° so that the direction
of the current lines up with the magnetic
field, what happens to the force?
13.
A square loop of current–carrying wire is placed
horizontally in a magnetic field that also is
oriented horizontally. Sketch the layout and
describe the forces on each segment of wire and
the resulting force or motion if the wire is able to
move freely.
14.
An electron passes through a northward magnetic
field of 0.40 T. It is determined that the electron
experiences an upward force of 9 × 10–12 N.
a.
What is the velocity (magnitude and
direction) of the electron?
b.
What force would a neutron experience
under these same conditions?
Physics P
15.
The speed of charged subatomic particles may be
calculated by measuring their curved orbits due to
centripetal forces when passing through a strong
magnetic field. If a proton circles in an orbit of
3.1 cm within a magnetic field of 8 T, how fast is
this proton moving?
16.
How strong and in what direction would a
magnetic field have to be to offset the force of
gravity acting on an electron traveling at a speed
of 9.5 × 107 m/s to the north?
17.
A 21–cm length of wire moves perpendicular to a
2.45–T magnetic field at 3.5 m/s.
a.
What is the magnitude of the EMF induced
in the wire?
b.
The wire is part of a circuit with a total
resistance of 3 Ω. What is the current
through the wire?
18.
An induced EMF of 0.089 V is induced in a 5–cm
wire when it is moved perpendicular to a magnetic
field at 2.1 m/s. What is the magnitude of the
magnetic field?
19.
An unknown length of wire moves perpendicular
to a 3.4–T magnetic field with a velocity of
12 m/s. If the induced EMF is 49 V, what is the
length of the wire?
20.
A straight wire that is oriented east-west is 28 cm
long moves northward through a downward
magnetic field of 2 T at a constant speed of
3.25 m/s. If the wire is 0.3 Ω, what is the
magnitude and direction of the induced current in
the wire?
21.
22.
Unit 9 Review: Magnets and Electromagnetism
Electrons moving at a speed of 1.8 × 106 m/s travel
undeflected through crossed electric and magnetic
fields. If the strength of the electric field is
4.2 × 103 N/C, what is the strength of the magnetic
field?
A wire carries a current of 6 A. The wire is at right
angles to a uniform magnetic field, and 0.8 m of
the wire is in the field. The force on the wire is
0.62 N. What is the strength of the magnetic field?
2
23.
A wire is at right angles to a uniform magnetic
field with magnetic induction of 0.4 T. The current
through the wire is 4 A. What is the force that acts
on the wire when 60 cm is in the field?
24.
A wire carries a current of 12 A. The wire is at
right angles to a uniform magnetic field that exerts
a force of 0.5 N on the wire when 2 m of the wire
is in the field. What is the strength of the magnetic
field?
25.
A wire is at right angles to a magnetic field that
exerts a force of 2.4 N on the wire. A current of
8.6 A flows through the wire. The induction of the
magnetic field is 0.66 T. What length of wire is in
the field?
26.
A high-speed electron travels at right angles to a
magnetic field that has an induction of 0.42 T. The
electron is traveling at 3.46 × 107 m/s. What is the
force acting on the electron?
27.
A straight wire that is 0.42 m long has a constant
speed of 12 m/s perpendicular to a magnetic field
that has a strength of 5.0 × 10-2 T.
a.
What is the induced EMF in the wire?
b.
If the wire is part of a circuit that has a
resistance of 2.25 Ω, what is the current
through the wire?
28.
A 25.5–m wire moves perpendicular to a magnetic
field of 4.42 × 10–4 T at a speed of 14.4 m/s. What
EMF is induced in the wire?
29.
The current carried through a wire is 13.4 mA.
The wire is connected across a circuit with 5.5 Ω
of resistance. If 1.12 m of the wire is moving
perpendicularly through a magnetic field of
0.25 T, then what is the velocity of the wire?
30.
A proton moving at a speed of 2 × 105 m/s enters a
magnetic field with a strength of 1.2 T and moves
in a circle. What is the radius of the proton’s path?
Physics P
1
Unit 9 Review: Magnets and Electromagnetism
F = ILB
(
)(
)(
F = 0.8$A 0.012$m 2.4$T
8
)
I=
9
F
LB
(
1.8$N
)(
0.24$m 0.75$T
)
The force is directed toward you.
3b
F = ILB
)(
)(
F = 26#A 0.005#m 0.75#T
10
)
F
LI
11a
(4.5$m)(2.1$A)
L=
F
IB
F = ILB
(
%C%=%2e
)(
)(
)
The direction of the force is to the north.
12a
Fg = FB
mg = ILB
mg
I=
LB
0.003$kg 9.8$m/s2
I=
0.15$m 8$T
(2$A)(6.5$T )
(
F = qvB
(
)(
)(
)
(
)(
)( )
)
I = 0.024$A
F = 3.1& × &10 −17 &N
12b
F = qvB
F
v=
qB
v=
)( )
−19
11b
2.99$N
F = 1.602& × &10 −19 &C 9.8& × &103 &m/s 0.02&T
7
F = qvB
F
q=
vB
4.32% × %10 −13 %N
q=
4.5% × %105 %m/s 3%T
The net force will be 1.44 N
L = 0.23$m
6
7
F = 0.144%N
F = ILB
L=
−19
F = 0.012%A 0.5%m 24%T
3.8$N
B = 0.40$T
5
(1.602$ × $10 $C)(8.6$ × $10 $m/s)
q = 3.2% × %10
F = ILB
B=
2.9$ × $10 −11 $N
(
F = 0.098#N
B=
"N
B = 2.1$T
3a
4
)(
F = qvB
F
B=
qv
B=
I = 10$A
(
)(
−14
The direction of the force is north.
F = ILB
I=
(
F = 2" × "1.602" × "10 −19 "C 4.1" × "10 4 "m/s 1.5"T
F = 2.0" × "10
F = 0.023$N
2
F = qvB
13
6.9$ × $10 −13 $N
(1.602$ × $10 $C)(1.35$T)
−19
v = 3.1$ × $106 $m/s
3
The force will become zero.
)
Physics P
14a
Unit 9 Review: Magnets and Electromagnetism
F = qvB
v=
v=
18
F
qB
B=
9" × "10 −12 "N
B=
(1.602" × "10 "C)(0.40"T)
−19
The force is directed to the west.
19
14b
A neutron would experience no force.
15
Fc = FB
)( )(
20
)
(9.11$ × $10
−31
)(
$kg 9.8$m/s
2
21
)
−19
V
R
BLv
I=
R
2"T 0.28"m 3.25"m/s
I=
0.3"Ω
I = 6.1"A
I=
)(
B=
The field needs to point to the east.
)(
)(
EMF = 2.45%T 0.21%m 3.5%m/s
FE = FB
E
v
4.2$ × $103 $N/C
B=
1.8$ × $106 $m/s
B = 0.0023$T
7
B = 5.9$ × $10 −19 $T
)
22
EMF = 1.8%V
17b
)
Eq = qvB
(1.602$ × $10 $C)(9.5$ × $10 $m/s)
(
)(
)
The current flows to the west.
mg
B=
qv
EMF = BLv
EMF = BLv
EMF
L=
Bv
49#V
L=
3.4#T 12#m/s
( )(
mg = qvB
17a
(0.05%m)(2.1%m/s)
L = 1.2#m
Fg = FB
B=
0.089%V
(
mv 2
= qvB
r
qBr
v=
m
1.602& × &10 −19 &C 8&T 0.031&m
v=
1.67& × &10 −27 &kg
v = 2.4& × &107 &m/s
(
EMF
Lv
B = 0.85%T
v = 1.4" × "108 "m/s
16
EMF = BLv
F = ILB
B=
V
R
1.8$V
I=
3$Ω
I = 0.6$A
I=
B=
F
LI
0.62%N
(0.8%m)(6%A)
B = 0.13%T
23
F = ILB
( )(
)(
F = 4"A 0.6"m 0.4"T
F = 0.96"N
4
)
Physics P
24
Unit 9 Review: Magnets and Electromagnetism
F = ILB
29
F
B=
LI
B=
0.5$N
(2$m)(12$A)
B = 0.021$T
25
(
(
F = ILB
L=
L=
F
IB
(
2.4$N
)(
8.6$A 0.66$T
30
)
F = qvB
(
)(
)(
F = 1.602& × &10 −19 &C 3.46& × &107 &m/s 0.42&T
F = 2.3& × &10
27a
−12
EMF = BLv
(
)
r = 0.0017&m
)(
)(
)
)(
)(
V
R
0.25%V
I=
2.25%Ω
I = 0.11%A
(
(1.67& × &10 &kg)(2& × &10 &m/s)
(1.602& × &10 &C)(1.2&T)
−27
I=
EMF = BLv
Fc = FB
r=
EMF = 0.25$V
28
)
)
mv 2
= qvB
r
mv
r=
qB
&N
EMF = 0.05$T 0.42$m 12$m/s
27b
)(
)(
v = 0.26&m/s
L = 0.42$m
26
V
R
BLv
I=
R
IR
v=
BL
0.0134&A 5.5&Ω
v=
0.25&T 1.12&m
I=
EMF = 4.42$ × $10 −4 $T 25.5$m 14.4$m/s
)
EMF = 0.16$V
5
5
−19