song (shs546) – Practice HW 5 Solutions – weathers – (22202)
1
This printout should have 19 questions.
Multiplechoice questions may continue on
the next column or page – fnd all choices
beFore answering.
001 (part 1 of 9) 10.0 points
A point charge
−
1 pC is concentric with two
spherical conducting thick shells, as show in
the fgure below. The smaller spherical con
ducting shell has a net charge oF
−
28 pC and
the larger spherical conducting shell has a net
charge oF
−
14 pC.
−
14 pC
−
28 pC
−
1 pC
P
1
P
2
P
3
P
4
P
5
0
.
8 cm
2
.
5 cm
4
.
2 cm
6
.
15 cm
8
.
45 cm
1
.
6 cm
3
.
4 cm
5 cm
7
.
3 cm
What is the charge on the inner surFace oF
the smaller spherical conducting shell, 1
.
6 cm
From the
−
1 pC point charge? Under static
conditions, the charge on a conductor resides
on the surFace oF the conductor.
Correct answer: 1 pC.
Explanation:
Let :
q
1
=
−
1 pC
and
r
P
2
= 2
.
5 cm
.
The net charge inside a Gaussian surFace lo
cated at
P
2
(
r
P
2
= 2
.
5 cm) must be zero
since the feld in the conductor must be zero.
ThereFore, the charge on the inner surFace oF
the smaller spherical conducting shell must be
−
q
1
.
002 (part 2 of 9) 10.0 points
What is the charge on the outer surFace oF
the smaller spherical conducting shell, 3
.
4 cm
From the
−
1 pC point charge?
Correct answer:
−
29 pC.
Explanation:
Let :
r
P
3
= 4
.
2 cm
and
q
2
=
−
28 pC
.
The net charge inside a Gaussian surFace
located at
P
3
(
r
P
3
= 4
.
2 cm) must be
q
1
+
q
2
since charge is conserved. ThereFore, the
charge on the outer surFace oF the smaller
spherical conducting shell must be
q
1
+
q
2
.
003 (part 3 of 9) 10.0 points
What is the charge on the inner surFace oF the
larger spherical conducting shell, 5 cm From
the
−
1 pC point charge?
Correct answer: 29 pC.
Explanation:
Let :
r
P
4
= 6
.
15 cm
.
The net charge inside a Gaussian surFace
located at
P
4
(
r
P
4
= 6
.
15 cm) must be zero
since the feld in the conductor must be zero.
ThereFore, the charge on the inner surFace oF
the large spherical conducting shell must be
−
(
q
1
+
q
2
).
004 (part 4 of 9) 10.0 points
What is the charge on the outer surFace oF the
larger spherical conducting shell, 7
.
3 cm From
the
−
1 pC point charge?
Correct answer:
−
43 pC.
Explanation:
Let :
r
P
5
= 8
.
45 cm
,
and
q
3
=
−
14 pC
.
The net charge inside a Gaussian surFace
located at
P
4
(
r
P
5
= 8
.
45 cm) must be
q
1
+
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2
q
2
+
q
3
since charge is conserved. Therefore,
the charge on the outer surface f the smaller
spherical conducting shell must be
q
1
+
q
2
+
q
3
.
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 Spring '00
 Littler
 Charge, Electrostatics, Potential Energy, Correct Answer, Electric charge

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