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ragsdale (zdr82) – HW7 – ditmire – (58335)
1
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beFore answering.
001
10.0 points
A wire carrying a current 30 A has a length
0
.
1 m between the pole Faces oF a magnet at
an angle 60
◦
(see the fgure). The magnetic
feld is approximately uniForm at 0
.
5 T. We
ignore the feld beyond the pole pieces.
(
θ
I
B
What is the Force on the wire?
Correct answer: 1
.
29904 N.
Explanation:
Let :
I
= 30 A
,
(
=0
.
1m
,
θ
= 60
◦
,
and
B
.
5T
.
we use
F
=
I ( B
sin
θ
, so
F
=
I ( B
sin
θ
= (30 A) (0
.
1 m) (0
.
5 T) sin60
◦
=
1
.
29904 N
.
002
10.0 points
The magnetic Force on a straight 0.45 m seg
ment oF wire carrying a current oF 4.5 A is
0.31 N.
What is the magnitude oF the component
oF the magnetic feld that is perpendicular to
the wire?
Correct answer: 0
.
153086 T.
Explanation:
Let :
(
.
45 m
,
I
=4
.
5A
,
and
F
m
.
31 N
.
The magnetic Force is
F
m
=
I ( B
B
=
F
m
I (
=
0
.
31 N
(4
.
5 A) (0
.
45 m)
=
0
.
153086 T
003
10.0 points
A rectangular loop oF wire hangs vertically as
shown in the fgure. A magnetic feld is di
rected horizontally, perpendicular to the wire,
and points out oF the page at all points as rep
resented by the symbol
±
. The magnetic feld
is very nearly uniForm along the horizontal
portion oF the wire
ab
(length is 0
.
1 m) which
is near the center oF a large magnet produc
ing the feld. The top portion oF the wire loop
is Free oF the feld. The loop hangs From a
balance which measures a downward Force (in
addition to the gravitational Force) oF 3
×
10

2
N when the wire carries a current 0
.
2 A.
a
b
II
F
(
B
What is the magnitude oF the magnet feld
B
at the center oF the magnet?
Correct answer: 1
.
5 T.
Explanation:
Let :
F
=3
×
10

2
,
(
.
,
and
I
.
2A
.
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View Full Document ragsdale (zdr82) – HW7 – ditmire – (58335)
2
The magnetic forces on the two vertical sec
tions of the wire loop point to the left and
right, respectively.
They are equal but in
opposite directions, so they add up to zero.
Thus the net magnetic force on the loop is that
on the horizontal section
ab
whose length is
(
=0
.
1 m (and
θ
= 90
◦
so sin
θ
= 1), and
B
=
F
I (
=
3
×
10

2
N
(0
.
2 A) (0
.
1 m)
=
1
.
5T
.
004
(part 1 of 4) 10.0 points
Two wires each carry a current
I
in the
xy
plane and are subjected to an external uni
form magnetic Feld
)
B
, which is directed along
the positive
y
axis as shown in the Fgure.
R
I
wire #2
I
wire #1
B
L
L
x
y
What is the magnitude of the force on wire
#1 due to the external
)
B
Feld?
1.
±
)
B
±
= (2
L
+
R
)
IB
2.
±
)
B
±
=
I
2
(2
L
+2
R
)
B
3.
±
)
B
±
=
±
L
+
R
2
²
4.
±
)
B
±
=2
I R L B
5.
±
)
B
±
=
I
(
L
+
R
)
B
6.
±
)
B
±
I
(
L
+
R
)
B
correct
7.
±
)
B
±
I L B
8.
±
)
B
±
=4
I
(
L
+
R
)
B
9.
±
)
B
±
=
(2
BL
R
)
I
10.
±
)
B
±
I R B
Explanation:
)
F
=
I
³
d)s
×
)
B
=
I
)
(
×
)
B.
±or wire 1,
)
(
⊥
)
B,
so the magnitude of
)
F
is
just
F
=
I ( B .
±or wire #1,
(
L
R.
Thus
F
=
2
I
(
R
+
L
)
B
.
005
(part 2 of 4) 10.0 points
What is the magnitude of the force on the
curved part of wire #2 due to the external
magnetic Feld?
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This note was uploaded on 11/03/2010 for the course PHYSICS 303 taught by Professor Shih during the Spring '10 term at University of Texas at Austin.
 Spring '10
 SHIH
 Current

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