Physics
4
March
1,2007
Exam
I
Calculators may be used, but no books or other
written
materials. Answer all
four
questions and show the steps leading to your answers. Credit will be given based on evidence
of your understanding of the material. Be sure to express all quantities in proper
units.
Potentially
useful information
Gauss7 Law:
jz
A
=
Qmc
/so
F=gE
4
surface area of a sphere
=
47r
r2
;
volume of a sphere
=
7r
r3
3
surface area of a cylinder
=
2n
r
L (side) +2n?(both ends); volume of a cylinder
=
7c
?L
V
=
IR
tIRC
i
=
ioe
,
charging a capacitor
Q=CV
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1.
Two
parts
(5
pts each):
a)
A
charge of
+4
nCis p1.aced at the
origin, and a charge of
+6
nC is placed
on the xaxis at
x
=
10
cm.
i.
At what location will the field
=
0
?
.
.
11.
What is the electric potential Vat this location?
b) What will be the charge on the
capacitor,
i.
Before switch
S
is closed?
.
.
11.
A
long time after switch
S
is closed?
2.
(10
pts)
6Jr.
In
the circuit shown on the right, what is the
current (magnitude and direction)
in
each of

3 0 ~
the three resistors?
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 Spring '07
 Cutts
 Physics, Electric charge, charge density, Van de Graff, volume charge density, Van De Graff Generator

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