fryer (vdf96) – Magnetics 2 Redo – graves – (6)
1
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printout
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have
18
questions.
Multiplechoice questions may continue on
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before answering.
001
10.0points
A vertical electric wire in the wall of a building
carries a DC current of 20 A upward.
I
x
S
N
E
(out)
What is the magnitude of the magnet field
at a point 0
.
1 m due north of this wire?
Correct answer: 40
μ
T.
Explanation:
Let :
I
= 20 A
.
The magnetic field due to a current carrying
wire at a distance
r
is
B
=
μ
0
I
2
π r
=
(4
π
×
10
−
7
T m) (20 A)
2
π
(0
.
1 m)
=
40
μ
T
.
002
10.0points
Will a pair of parallel currentcarrying wires
exert forces on each other?
1.
No; the magnetic field generated by the
currents of the wires does not affect the wires
themselves.
2.
Yes; the magnetic field generated by the
current in one wire is perpendicular to the
current in the other wire and vise versa.
cor
rect
3.
No; no net magnetic field is generated.
4.
No; the two wires attract each other by
the magnetic field generated by their currents
and repel each other due to the like charges
of the moving particles in the wires. The two
forces are equal in magnitude.
5.
Yes; the wires are electrically charged.
Explanation:
The magnetic fields generated by the cur
rents of the wires are perpendicular to the
currents and according to the righthand rule
they exert forces on those wires. Both wires
are neutral as a whole, so there is no electric
force between them.
003(part1of2)10.0points
A magnetic field of 0
.
8 T is perpendicular to
a square coil of 18 turns. The length of each
side of the coil is 4 cm.
Find the magnetic flux through an individ
ual turn of the coil.
Correct answer: 1
.
28 mWb.
Explanation:
Let :
B
= 0
.
8 T
,
N
= 18
,
ℓ
= 4 cm = 0
.
04 m
,
and
θ
= 0
◦
.
The magnetic flux is
Φ =
B A
cos
θ
=
B ℓ
2
cos
θ
= (0
.
8 T) (0
.
04 m)
2
cos 0
◦
·
10
3
mWb
1 Wb
=
1
.
28 mWb
.
004(part2of2)10.0points
Find the magnetic flux through an individual
turn of the coil if the magnetic field makes an
angle of 60
◦
with the normal to the plane of
the coil.
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fryer (vdf96) – Magnetics 2 Redo – graves – (6)
2
Correct answer: 0
.
64 mWb.
Explanation:
Let :
θ
= 60
◦
.
The magnetic flux is
Φ =
B A
cos
θ
=
B ℓ
2
cos
θ
= (0
.
8 T) (0
.
04 m)
2
cos 60
◦
·
10
3
mWb
1 Wb
=
0
.
64 mWb
.
keywords:
005(part1of2)10.0points
A long,
straight wire carries a current of
17
.
7 A. An electron travels at 1
.
09
×
10
5
m
/
s
parallel to the wire, 54
.
5 cm from the wire.
The
permeability
of
free
space
is
1
.
25664
×
10
−
6
N
/
A
2
and the charge on an
electron is 1
.
6
×
10
−
19
C.
What force does the magnetic field of the
current exert on the moving electron?
Correct answer: 1
.
1328
×
10
−
19
N.
Explanation:
Let :
μ
0
= 1
.
25664
×
10
−
6
N
/
A
2
,
v
= 1
.
09
×
10
5
m
/
s
,
q
= 1
.
6
×
10
−
19
C
,
I
= 17
.
7 A
,
and
r
= 54
.
5 cm = 0
.
545 m
.
Magnetic
field
produced
by
a
straight,
currentcarrying wire is
B
=
μ
0
I
2
π r
=
(4
π
×
10
−
7
) (17
.
7 A)
2
π
(0
.
545 m)
= 6
.
49541
×
10
−
6
T
.
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 Fall '10
 Graves
 Physics, Magnetic Field, fryer

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