Platt, David – Homework 17 – Due: Oct 17 2005, 4:00 am – Inst: Ken Shih
1
This
printout
should
have
6
questions.
Multiplechoice questions may continue on
the next column or page – find all choices
before answering.
The due time is Central
time.
Please learn chapter 30, section 1 by your
self to solve some of these problems.
This
section will be included in Quiz2.
001
(part 1 of 2) 10 points
Assume:
The mobile charge carriers are ei
ther
electrons
or
holes.
The
holes
have
the same magnitude of charge as the elec
trons.
The number of mobile charge car
riers
for
this
particular
material
is
n
=
8
.
49
×
10
28
electrons
/
m
3
.
Note:
In the figure, the point at the upper
edge
P
1
and at the lower edge
P
2
have the
same
x
coordinate.
A constant magnetic field of magnitude
points out of the paper.
There is a steady
flow of a horizontal current flowing from left
to right in the
x
direction.
2.2 m
4
.
9 cm
6 cm
7
.
5 A
P
1
P
2
V
~
B
B
= 1
.
2 T
y
x
The charge on the electron is 1
.
6021
×
10

19
C.
What is the magnitude of the electric field
between the upper and lower surfaces?
Correct answer: 2
.
2506
×
10

7
N
/
C.
Explanation:
Let :
a
= 6 cm = 0
.
06 m
,
b
= 4
.
9 cm = 0
.
049 m
,
B
= 1
.
2 T
,
n
= 8
.
49
×
10
28
electrons
/
m
3
,
q
= 1
.
6021
×
10

19
C
,
I
= 7
.
5 A
,
and
L
= 2
.
2 m
.
L
b
a
I
P
1
P
2
V
~
B
~
B
y
x
For the Hall effect the magnetic force bal
ances the electric force which means
q v
d
B
=
q E ,
or
E
=
v
d
B .
Also we know
I
=
n q v
d
A
or
v
d
=
I
n q A
,
so that the magnitude of the electric field is
E
=
I B
n q A
=
(7
.
5 A) (1
.
2 T)
n
(1
.
6021
×
10

19
C) (0
.
00294 m
2
)
=
2
.
2506
×
10

7
N
/
C
,
where the area
A
=
a
·
b
= (0
.
06 m) (0
.
049 m)
= 0
.
00294 m
2
.
002
(part 2 of 2) 10 points
For this part of the problem a voltmeter (with
an internal resistance less than infinity) is
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Platt, David – Homework 17 – Due: Oct 17 2005, 4:00 am – Inst: Ken Shih
2
connected to the system, where the contact
points are on the upper and lower surfaces
and are in the same vertical plane.
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 Fall '08
 Turner
 Physics, Work, Magnetic Field, Ken Shih

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