17.43. Set Up:
For a point charge,
is toward a negative charge and away from a positive charge. Let
and
For the net electric field to be zero,
and
must have equal magnitudes
and opposite directions.
Figure 17.43
Solve:
The two charges and the directions of their electric fields in three regions are shown in Figure 17.43a. Only in
region II are the two electric fields in opposite directions. Consider a point a distance
x
from
so a distance
from
gives
and
is the positive solution. The electric field is zero at a point between the two charges, 0.24 m from the
0.500 nC charge.
(b)
Let
be the negative charge. The two charges and the directions of their electric fields in three
regions are shown in Figure 17.43b.
and
are in opposite directions in regions I and III. But for the magni
tudes of the fields to be equal the point must be closer to the charge
that has smaller magnitude, and that
occurs only for region I. Consider a point a distance
x
to the left of
so
from
gives
and
is the positive solu
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This note was uploaded on 03/06/2009 for the course PHYS 114 taught by Professor Shoberg during the Spring '07 term at Pittsburg State Uiversity.
 Spring '07
 Shoberg
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