homework 04 – KANUNGO, ANIL – Due: Sep 11 2007, 4:00 am
1
Question 1, chap 23, sect 3.
part 1 of 4
10 points
Consider symmetrically placed rectangular
insulators with uniformly charged distribu
tions of equal magnitude as shown in the fig
ures.
x
y
++++

Find the net electric field at the origin.
1.
aligned with the positive
y
axis
2.
aligned with the positive
x
axis
3.
aligned with the negative
y
axis
4.
nonzero and not aligned with either the
x
 or
y
axis
5.
aligned with the negative
x
axis
correct
6.
zero with the direction undefined.
Explanation:
At the origin, the positive slab of charge
produces
an
electric
field
pointed
toward
quadrant
III
(away
from
the
positively
charged slab).
The negatively charged slab
produces an electric field of equal magnitude
(as the positively charged slab) but pointing
toward quadrant II (toward the negatively
charged slab). The
x
components of the two
fields add (producing
E
x
<
0), while the
y

components cancel. Thus the electric field is
along the negative
x
axis.
Question 2, chap 23, sect 3.
part 2 of 4
10 points
x
y
++++
++++
In the figure above what is the net field at
the origin?
1.
aligned with the negative
y
axis
2.
aligned with the positive
y
axis
3.
nonzero and not aligned with either the
x
 or
y
axis
4.
aligned with the negative
x
axis
5.
zero and the direction is undefined
cor
rect
6.
aligned with the positive
x
axis
Explanation:
At the origin the upper slab produces an
electric field that points toward quadrant III
(away from the positively charged slab) and
the lower slab an electric field that is points
toward quadrant I (away from the positively
charged slab). By symmetry, these two elec
tric fields are equal in magnitude and opposite
in direction, so the total electric field sums to
zero.
Question 3, chap 23, sect 3.
part 3 of 4
10 points
x
y
   
+ + + +
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homework 04 – KANUNGO, ANIL – Due: Sep 11 2007, 4:00 am
2
In the figure above what is the net field at
the origin?
1.
aligned with the positive
y
axis
2.
zero with an undefined direction
3.
aligned with the positive
x
axis
4.
aligned with the negative
y
axis
5.
aligned with the negative
x
axis
6.
nonzero and not aligned with either the
x
 or
y
axis
correct
Explanation:
As in the previous Part, at the origin the
upper slab produces an electric field pointing
toward quadrant III (away from the positively
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 Fall '08
 Turner
 Charge, Work, Electric charge, 5 %, Anil, positively charged slab

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