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AP Physics 2
Electric Potential & Voltage
1. If two points are at the same potential , does it mean that no net work is done in moving a
test charge from one point to the other? Does this imply that no force must be exerted?
Explain. (Giancoli 17 Q1)
2. A conducting sphere carries charge Q and a second conducting sphere is neutral. The two
are initially isolated but then they are placed in contact. What can you say about the
potential of each when they are in contact? Will the charge flow from one to the other? If
so, how much? (Giancoli 17 Q11)
3. Four identical point charges are arranged at the corners of a square. The electric field E
and the potential V at the center of the square are…
o A. E = 0, V = 0
o B. E = 0, V  0
o C. E  0, V  0
o D. E = 0, V = 0
o E. E = V, regardless of value
Explain your answer. (Giancoli 17 MQ3)
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4. Four charges of equal magnitude, but possibly different signs, are placed on the corners of a
square. What arrangement of charges will produce an electric field with the greatest
magnitude at the center of the square? (Giancoli, Exercise 16.G)
o A. All four charges of the same sign
o B. Three charges of the same sign and one charge with a different sign
o C. Two positive charges and two negative charges
Explain your answer.
5. A +2.0 C charge is in an electric field. What happens if that charge is replaced by a
-2.0 C charge?
o A. The electric potential changes sign, but the electrical potential energy stays the
same.
o B. The electric potential stays the same, but the electric potential energy changes
sign.
o C. Both the electric potential and electric potential energy change sign.
o D. Both the electric potential and electric potential energy stay the same.
Explain your answer. (Giancoli 17 MQ11)
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6. In a thunderstorm, charge is separated though a complicated mechanism that is ultimately
powered by the sun. A simplified model of the charge in a thundercloud represents positive
charge accumulated at the top and the negative charge accumulated at the bottom. What is
the electric potential energy of a 50 C charge and a -20 C charge separated by 8 km?
(Giambattista, ex 17.1)
7. Two point charges, X=+6.0 C and Y=+5.0 C, are separated by 15.0 m. (adapted from
Giambattista, practice problem 17.1)
a) What is the electric potential energy between X and Y?
b) Assume charge X is fixed in place. Even if no other forces act on charge Y, charge Y will
move away from charge X. Is energy conserved in this situation? Explain why or why
not.
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Use the diagram at right to answer questions 8-9.
8. Find the electric potential energy for the array of charges
shown at right.
q2 = +2.0 C
4.0 m
3.0 m
q1 = +4.0 C
q3 = -3.0 C
9. What would the potential energy be if q3 were positive instead of negative?
10. Draw a conductor in the oblong shape of a football. This conductor carries a net negative
charge, -Q. Draw in a dozen or so electric field lines and equipotential lines. (Giancoli
17.17)
11. In a photocell, ultraviolet light provides enough energy to some electrons in barium metal
to eject them from the surface at high speed. To measure the maximum energy of the
electrons, another above the barium is kept at a negative
enough potential that the emitted electrons are slowed
down and stopped, and return to the barium surface. If
the plate voltage is -3.02 V (compared to the barium)
when the fastest electrons are stopped, what are the
speed of these electrons when they were emitted?
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Equipotential Problem Set
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