mcconnell (kam2342) – oldhomework 11 – Turner – (60230)
1
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printout
should
have
6
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001
(part 1 of 2) 10.0 points
The quantity of charge passing through a sur
face of area 0
.
99 cm
2
varies with time as
q
=
q
1
t
3
+
q
2
t
+
q
3
,
where
q
1
= 4
.
5 C
/
s
3
,
q
2
= 2
.
3 C
/
s,
q
3
= 7
.
5 C,
and
t
is in seconds.
What is the instantaneous current through
the surface at
t
= 0
.
5 s?
Correct answer: 5
.
675 A.
Explanation:
Let :
q
1
= 4
.
5 C
/
s
3
,
q
2
= 2
.
3 C
/
s
,
q
3
= 7
.
5 C
,
and
t
= 0
.
5 s
.
I
≡
d q
dt
= 3
q
1
t
2
+
q
2
= 3
(
4
.
5 C
/
s
3
)
(0
.
5 s)
2
+ 2
.
3 C
/
s
=
5
.
675 A
.
002
(part 2 of 2) 10.0 points
What is the value of the current density at
t
= 0
.
5 s?
Correct answer: 57323
.
2 A
/
m
2
.
Explanation:
Let :
a
= 0
.
99 cm
2
= 9
.
9
×
10

5
m
2
and
t
= 0
.
5 s
.
J
≡
I
A
=
5
.
675 A
9
.
9
×
10

5
m
2
=
57323
.
2 A
/
m
2
.
003
10.0 points
The compressor on an air conditioner draws
55.0 A when it starts up.
If the startup time is 0.65 s, how much
charge passes a crosssectional area of the
circuit in this time?
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 Spring '10
 Turner
 Correct Answer, Electric charge, McConnell

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