brown (twb493) – Ch18-h4 – chiu – (56565)
1
This
print-out
should
have
29
questions.
Multiple-choice questions may continue on
the next column or page – find all choices
before answering.
001(part1of6)5.0points
Conventional current flows through the ring
shown in the figure below in such a way that
if you stand at location A on the +
x
axis
and look towards the ring, current appears to
be flowing clockwise. The ring lies in the
yz
plane, encircling the
x
axis.
x
z
y
A
B
C
D
E
F
What is the direction of the magnetic field
due to the ring at A?
1.
ˆ
B
A
=
(
0
,
1
,
0
)
2.
ˆ
B
A
=
(
0
,
0
,
1
)
3.
ˆ
B
A
=
(
0
,
0
,
−
1
)
4.
ˆ
B
A
=
(
0
,
−
1
,
0
)
5.
ˆ
B
A
=
(−
1
,
0
,
0
)
correct
6.
ˆ
B
A
=
(
1
,
0
,
0
)
Explanation:
Given the direction in which the current
is traveling around the ring, we can use the
right hand rule to find that the magnetic field
must point along the
−
x
axis. Therefore the
correct choice for point A is
ˆ
B
A
=
(−
1
,
0
,
0
)
.
002(part2of6)5.0points
At B?
1.
ˆ
B
B
=
(
1
,
0
,
0
)
correct
2.
ˆ
B
B
=
(
0
,
−
1
,
0
)
3.
ˆ
B
B
=
(
0
,
1
,
0
)
4.
ˆ
B
B
=
(
0
,
0
,
−
1
)
5.
ˆ
B
B
=
(−
1
,
0
,
0
)
6.
ˆ
B
B
=
(
0
,
0
,
1
)
Explanation:
At any point in the plane of the ring and
inside the ring, the magnetic field is pointing
through the ring along the
−
x
axis.
At any
point in the plane of the ring but
outside
of the
ring, like B, D, E, and F, the magnetic field
lines will be wrapping back around toward the
positive
x
axis to travel back through the ring
again.
So at these points the correct choice
for the direction of the magnetic field is
ˆ
B
=
(
1
,
0
,
0
)
.
003(part3of6)5.0points
At C?
1.
ˆ
B
C
=
(
0
,
0
,
−
1
)
2.
ˆ
B
C
=
(
0
,
1
,
0
)
3.
ˆ
B
C
=
(
0
,
−
1
,
0
)
4.
ˆ
B
C
=
(
1
,
0
,
0
)
5.
ˆ
B
C
=
(
0
,
0
,
1
)
6.
ˆ
B
C
=
(−
1
,
0
,
0
)
correct
Explanation:
See the explanation for part 1.
004(part4of6)5.0points
At D?
1.
ˆ
B
D
=
(
0
,
−
1
,
0
)
2.
ˆ
B
D
=
(
0
,
1
,
0
)
3.
ˆ
B
D
=
(
0
,
0
,
1
)