Download Phys115 attend Epotentials sol

Phy 115: Attend: Electrical Potential Energy Name ________________________
1. At the right is a diagram showing some equipotential
lines resulting from the charged surface shown and
some lettered locations (A-G). (7 pts)
E
D
F
C
a) Draw at least 5 Electric Field lines.
I drew 2. Make sure to keep them perpendicular to
equipotential lines and put on arrows.
b) Is the shaded charged surface positive or negatively
charged? How do you know?
Negative as the E-Field lines are downhill toward it.
c) Find the location (A-G) where the Electric Field
will be the least.
G
B
A
-100V
-75V
E where equipotential lines are most spread.
d) Is the work done by the electric field in moving a
-50V
+4 C point charge from B to D, positive, negative,
or zero? Explain.
Work is F * delta r. Force is opposite motion so work
is negative.
e) How much work is done by the electric field in moving a +4 C point
charge from B to D? Explain.
-25V
f) Find a location (A-G) that is at a higher electrical potential than at D.
There is not one.
g) Find a location (A-G) where a positive test charge would have a higher
electrical potential energy than at D.
There is not one.
2. Charges are placed as indicated in diagram A. The electrical potential energy
in this situation is UA. The same charges are used in diagram Band the shaded
charge was moved. The electrical potential energy for this situation will be
called UB. (3 pts)
a) Is UA positive or negative? Positive
+
UB
UA
U=0
b) Place UA and UB on the energy number-line at the right so that the
relative sizes might be compared. r is less so U is greater
A
B
Phy 115-Attend6
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