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Electric Fields, Electric Potential Energy, and Electric Potential
Electric Fields (Note: The charge on the electron is 1.60 x 10-19C)
1. A positive charge of 1.0 x 10-5 C experiences a force of .20 N when located at a certain point. What is the
electric field intensity at that point?
2. What charge exists on a test charge that experiences a force of 1.4 x 10-8 N at a point where the electric
field intensity is 2.0 x 10-4 N/C?
3. The electric field is the atmosphere is about 150 N/C downward.
a. What is the direction of the force on a positively-charged particle?
b. Find the electric force on a proton with charge +1.6 x 10-19 C
c. Compare the force in part b with the force of gravity on the same proton
(mass 1.7 x 10-27 kg).
4. A charge, q1 = 5.00 μC, is at the origin, and a second charge q2 = -3.00 μC, is on the x-axis is 0.800 m
from the origin. Find the electric field at a point on the y-axis 0.500 m from the origin. Be sure to draw a
diagram including all of the charges and the electric field vectors.
Diagram:
5. A proton and an electron in a hydrogen atom are separated on the average by about 5.3 X 10-11 m. What
is the magnitude and direction of the electric field set up by the proton at the position of the electron?
6. If 120 J of work are done to move one coulomb of charge from a positive plate to a negative plate, what
voltage difference exists between the plates?
7. How much work is done to transfer .15 C of charge through a potential difference of 9.0 V?
Electric Potential Energy
8. Two alpha particles (helium nuclei), each consisting of two protons and two neutrons, have an electrical
potential energy of 6.32 x 10-19J. What is the distance between these particles at this time?
9. In a charging process, 1013 electrons are removed from a metal sphere and placed on a second sphere that
is initially uncharged. Then the electrical potential energy associated with the two spheres is found to be
-0.072 J.
10. A charge moves a distance of 2.0 cm in the direction of a uniform electric field having a magnitude of
215 N/C. The electrical potential energy of the charge decreases by 6.9 x 10-19 J as it moves. Find the
magnitude of the charge on the moving particle. (Hint: The electrical potential energy depends on the
distance moved in the direction of the field.)
Electrical Potential
11. Find the Electric Potential at a point 1.0 cm from a proton.
12. Two point charges of magnitude 5.0 nC and -3.0 nC are separated by 35.0 cm. What is the electric
potential at a point midway between the charges?
13. Four particles with charges of 5.0 μC, 3.0 μC, 3.0 μC, and -5.0 μC, are placed at the corners of a 2.0 m x
2.0 m square. Determine the electric potential at the center of the square.
Work done on a Charge, Uniform Electric Fields, and Capacitors
Work done on a charge moving through an electric field
1. A 12-V battery does 1200 J of work transferring charge. How much charge is transferred?
2. A force 0.053 N is required to move a charge of 37 μC a distance of 25 cm in an electric field. What is the
size of the potential difference between the two points?
Uniform Electric Fields
3. The electric field intensity between two charged plates is 1.5 x 103 N/C. The plates are 0.080 m apart.
What is the potential difference, in volts, between them?
Capacitors
4. A 5.4-μC capacitor is charged with 2.7 x 10-3 C. What potential difference exists across it?
5. A 4.00 μF capacitor is connected to a 12.0 V battery.
a. What is the charge on each plate of the capacitor?
b. If this same capacitor is connected to a 1.5 V battery, how much electrical potential energy is
stored?
6. A parallel-plate capacitor has a charge of 6.0 μC when charged by a potential difference of 1.25 B.
a. Find its capacitance.
b. How much electrical potential energy is stored when this capacitor is connected to a 1.50 V
battery?
7. A capacitor has a capacitance of 2.00 pF.
a. What potential difference would be required to store 18.0 pC?
b. How much charge is stored when the potential difference is 2.5 V?
8. Your are asked to design a parallel-plate capacitor having a capacitance of 1.00 F and a plate separation
of 1.00 mm. Calculate the required surface area of each plate. Is this a realistic size for a capacitor?