homework 12 – LEE, BENJAMIN – Due: Oct 2 2007, 4:00 am
1
Question 1, chap 27, sect 1.
part 1 of 1
10 points
How long does it take for 14 C of charge to
pass through a crosssectional area of a copper
wire if
I
= 15 A?
Correct answer: 0
.
933333 s (tolerance
±
1
%).
Explanation:
Let :
I
= 15 A and
Δ
Q
= 14 C
.
I
=
Δ
Q
Δ
t
Δ
t
=
Δ
Q
I
=
14 C
15 A
=
0
.
933333 s
.
Question 2, chap 27, sect 2.
part 1 of 3
10 points
Consider two cylindrical conductors made
of the same ohmic material. Conductor 1 has
a radius
r
1
and length
ℓ
1
while conductor 2
has a radius
r
2
and length
ℓ
2
.
Denote:
The currents of the two conductors
as
I
1
and
I
2
, the potential diFerences between
the two ends of the conductors as
V
1
and
V
2
,
and the electric ±elds within the conductors
as
E
1
and
E
2
.
V
1
v
E
I
ℓ
r
1
b
2
r
2
b
If
ρ
2
=
ρ
1
, r
2
= 2
r
1
, ℓ
2
= 3
ℓ
1
and
V
2
=
V
1
, ±nd the ratio
R
2
R
1
of the resistances.
1.
R
2
R
1
= 4
2.
R
2
R
1
= 2
3.
R
2
R
1
=
2
3
4.
R
2
R
1
=
1
3
5.
R
2
R
1
=
3
2
6.
R
2
R
1
=
3
4
correct
7.
R
2
R
1
=
4
3
8.
R
2
R
1
=
1
4
9.
R
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 Fall '07
 Turner
 Charge, Work, Ratio, Resistor, Harshad number, Electrical resistance, E1 E2 E1

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