Patel, Kinal – Homework 8 – Due: Feb 19 2008, 7:00 pm – Inst: Weathers
1
This
printout
should
have
11
questions.
Multiplechoice questions may continue on
the next column or page – find all choices
before answering.
The due time is Central
time.
001
(part 1 of 2) 10 points
The quantity of charge passing through a sur
face of area 1
.
96 cm
2
varies with time as
q
=
q
1
t
3
+
q
2
t
+
q
3
,
where
q
1
= 4
.
7 C
/
s
3
,
q
2
= 3
.
7 C
/
s,
q
3
= 2
.
4 C,
and
t
is in seconds.
What is the instantaneous current through
the surface at
t
= 0
.
8 s?
Correct answer: 12
.
724 A.
Explanation:
Let :
q
1
= 4
.
7 C
/
s
3
,
q
2
= 3
.
7 C
/
s
,
q
3
= 2
.
4 C
,
and
t
= 0
.
8 s
.
I
≡
d q
dt
= 3
q
1
t
2
+
q
2
= 3
(
4
.
7 C
/
s
3
)
(0
.
8 s)
2
+ 3
.
7 C
/
s
=
12
.
724 A
.
002
(part 2 of 2) 10 points
What is the value of the current density at
t
= 0
.
8 s?
Correct answer: 64918
.
4 A
/
m
2
.
Explanation:
Let :
a
= 1
.
96 cm
2
= 0
.
000196 m
2
and
t
= 0
.
8 s
.
J
≡
I
A
=
12
.
724 A
0
.
000196 m
2
=
64918
.
4 A
/
m
2
.
keywords:
003
(part 1 of 1) 10 points
A conductor with crosssectional area 7 cm
2
carries a current of 12 A.
If the concentration of free electrons in the
conductor is 9
×
10
28
electrons
/
m
3
, what is
the drift velocity of the electrons?
Correct answer: 0
.
00118886 mm
/
s.
Explanation:
Let :
I
= 12 A
,
n
= 9
×
10
28
electrons
/
m
3
,
q
e
= 1
.
60218
×
10

19
C
,
and
A
= 7 cm
2
= 0
.
0007 m
2
.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '08
 Weathers
 Electron, Work, Correct Answer, 1 min, 0.219 mm, 0.438 mm

Click to edit the document details