maini (nm7637) – hw7 – Shneidman – (12108)
1
This
printout
should
have
9
questions.
Multiplechoice questions may continue on
the next column or page – find all choices
before answering.
001
(part 1 of 2) 10.0 points
The potential difference in a simple circuit is
22 V and the resistance is 30 Ω.
What current
I
flows in the circuit?
Correct answer: 0
.
733333 A.
Explanation:
Let :
V
= 22 V
and
R
= 30 Ω
.
The current is
I
=
V
R
=
22 V
30 Ω
=
0
.
733333 A
.
002
(part 2 of 2) 10.0 points
How many electrons pass a given point in the
circuit in 9 min?
Correct answer: 2
.
475
×
10
21
.
Explanation:
Let :
I
= 0
.
733333 A
,
t
= 9 min = 540 s
,
and
q
e
= 1
.
6
×
10
−
19
C
.
I
=
q
t
, where
q
is in coulombs and
t
in seconds;
that is,
q
=
I t,
and the total charge for
n
electrons is
q
=
n q
e
,
so
n
=
q
q
e
=
I t
q
e
=
(0
.
733333 A) (540 s)
1
.
6
×
10
−
19
C
=
2
.
475
×
10
21
.
003
10.0 points
A 2
.
6 cm length of tungsten filament in a
small lightbulb has a resistance of 0
.
073 Ω.
Find
its
diameter.
(The
resistivity
is
5
.
6
×
10
−
8
Ω
·
m).
Correct answer: 0
.
159358 mm.
Explanation:
Let :
L
= 2
.
6 cm = 0
.
026 m
,
R
= 0
.
073 Ω
,
and
ρ
= 5
.
6
×
10
−
8
Ω
·
m
.
Resistance is
R
=
ρ L
A
=
ρ L
π
parenleftbigg
d
2
parenrightbigg
2
=
4
ρ L
π d
2
,
d
=
radicalbigg
4
ρ L
π R
=
radicalBigg
4 (5
.
6
×
10
−
8
Ω
·
m) (0
.
026 m)
π
(0
.
073 Ω)
×
parenleftbigg
1000 mm
1 m
parenrightbigg
=
0
.
159358 mm
.
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 Spring '08
 moro
 Resistor, SEPTA Regional Rail, Jaguar Racing, Electrical resistance, Series and parallel circuits, JenkintownWyncote

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