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AP Physics 2
Electric Potential Energy
1. An electron with mass 9.1 x 10-31 kg and charge of -1.6 x 10-19 C and a proton with a mass of
1.67 x 10-27 kg and a charge of 1.6x10-19 C are 1 m apart.
𝑚 𝑚
a) What is the force of gravitational attraction between the two charges? Hint: 𝐹 = 𝐺 𝑟1 2 2
b) What is the force of electrical attraction between the two charges?
2. Use field line conventions to draw the field lines associated with two charges separated by a short
distance: +3q and -6q.
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3. Use field line conventions to draw field lines associated with three charges spaced equilaterally:
each with +2q.
4. Four objects, each with charge +q, are held fixed on a square with
sides of length d, as shown in the figure to the right. Objects X and
Z are at midpoints of the sides of the square. The electrostatic
force exerted by object W on object X is F. What is the magnitude
of the net force exerted on object X by objects W, Y, and Z?
Explain your answer. (AP sample test)
5. Three charges are arranged as shown in the diagram to the
right. In what direction will the resulting electric field at spot
P point? P is on the same line as the -12q charge and the +3q
charge, but twice as far from -12q charge as it is from the +3q
charge. Justify your answer. (Knight 20-28)
d
-1q
P
+3q
-12q
½d
d
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6. The figure at right shows electric field lines due to a point charge. What can
you say about the field at point 1 compared to the field at point? (Giancoli,
MS 16-4)
A. The field at point 2 is larger, because point 2 is on a field line.
B. The field at point 1 is larger, because point 1 is NOT on a field line.
C. The field at point 1 is zero, because point 1 is NOT on a field line.
D. The field at point 1 is larger, because the field lines are closer
together in that region.
2
1
+
Explain why the wrong answers are wrong.
7. A charge Q is transferred from an initially uncharged plastic ball to an identical ball. If the force of
attraction 17 mN when the balls are 0.24 m apart, how many electrons were transferred from one
ball to the other? (Giancoli 16-12)
8. Briefly describe how a photocopier uses electrostatics to produce an image.
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9. A +1.0-C charged object and a +2.0-C charged object are separated by 100 m. Where should a
-1.0 x 10-3-C-charged object be located on a line between the positively charged objects so that the
net electrical force on the negatively-charged object is zero? (Etkina, 14-18)
10. Earth has an excess of 60 electrons on each square centimeter of surface. (Etkina, 14-5)
a. Determine the electric charge (in coloumbs) on each square centimeter.
b. If 10-22 kg of electrons transfer to your body as you walk across the rug, estimate the
number of electrons and the total charge (in coloumbs) on your body.
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