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Nguyen, Thanh – Homework 1 – Due: Jan 22 2008, 7:00 pm – Inst: Weathers
1
This
printout
should
have
8
questions.
Multiplechoice questions may continue on
the next column or page – fnd all choices
beFore answering.
The due time is Central
time.
001
(part 1 oF 1) 10 points
1) Two uncharged metal balls,
Y
and
X
, each
stand on a glass rod and are touching.
X
Y
2) A third ball carrying a positive charge, is
brought near the frst two.
X
Y
+
3) While the positions oF these balls are fxed,
ball
Y
is connected to ground.
X
Y
+
4) Then the ground wire is disconnected.
X
Y
+
5) While
Y
and
X
remain in touch, the ball
carring the positive charge is removed.
X
Y
6) Then ball
Y
and
X
are separated.
X
Y
AFter these procedures, the signs oF the
charge
q
Y
on
Y
and
q
X
on
X
are
1.
q
Y
is neutral and
q
X
is positive.
2.
q
Y
is neutral and
q
X
is negative.
3.
q
Y
is negative and
q
X
is negative.
cor
rect
4.
q
Y
is negative and
q
X
is positive.
5.
q
Y
is negative and
q
X
is neutral.
6.
q
Y
is positive and
q
X
is positive.
7.
q
Y
is neutral and
q
X
is neutral.
8.
q
Y
is positive and
q
X
is neutral.
9.
q
Y
is positive and
q
X
is negative.
Explanation:
When the ball with positive charge is
brought nearby, the Free charges inside
Y
and
X
rearrange themselves.
The negative
charges are attracted and go to the right (
i.e.
move to
X
), whereas the positive charges are
repelled and collect in the leFt hand side oF the
system
Y Y
,
i.e.,
in
Y
.
When we ground
Y
, the positive charges
which have collected in
Y
are allowed to es
cape (they strive to the leFt), whereas the
negative charges in
X
are still held enthralled
by the positive charge on the third ball. We
break the ground.
Now we remove the third ball with positive
charge. The charge on
X
is redistributed in
the system
Y Y
,
i.e.
they share the negative
charge (equally iF identical).
±inally we separate
Y
and
X
. The signs
oF the charge on
Y
and that on
X
are both
negative.
keywords:
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View Full DocumentNguyen, Thanh – Homework 1 – Due: Jan 22 2008, 7:00 pm – Inst: Weathers
2
002
(part 1 of 1) 10 points
Four
point
charges,
each
of
magnitude
15
.
18
μ
C, are placed at the corners of a square
79
.
2 cm on a side.
The
value
of
Coulomb’s
constant
is
8
.
98755
×
10
9
N
·
m
2
/
C
2
.
If three of the charges are positive and one
is negative, ±nd the magnitude of the force
experienced by the negative charge.
Correct answer: 6
.
32011 N.
Explanation:
Let :
k
e
= 8
.
98755
×
10
9
N
·
m
2
/
C
2
,
d
= 79
.
2 cm = 0
.
792 m
,
and
Q
= 15
.
18
μ
C = 1
.
518
×
10

5
C
.
F
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