Download 017 Electric Potential

Chapter 17 Electric Potential
1. Doubling both charges changes the potential energy for a pair of point charges by a factor of:
A. 2.
B. 4.
C. ½.
D. ¼.
E. 1 (no change).
4. What is the distance between a -2.00 μC charge and a -3.00 μC charge if their potential energy is 0.491 J?
A. 25.0 cm
B. 15.5 cm
C. 11.0 cm
D. 3.14 cm
E. 0.911 cm
8. Three 1.0 μC charges are placed along the x-axis, one charge at x = -10 cm, another at the origin, and the last
one at x = 10 cm. What is the total potential energy of this arrangement?
A. 0.27 J
B. -0.27 J
C. 0.72 J
D. 0.23 J
E. infinite (or indeterminate)
10. Three point charges, q1, q2, and q3, are located at the vertices of an equilateral triangle. If q1 = q2, what value
must q3 have so that the total potential energy of the arrangement is zero?
A. q1
B. 0.5 q1
C. -0.5 q1
D. (q1 + q2)/2
E. No value will have this result.
12. A 2.5-mC charge is on the y-axis at y = 3.0 m and a 6.3-mC charge is on the x-axis at x = 3.0 m. What is the
direction of the potential at the origin?
A. 22.0°
B. 168°
C. 292°
D. 332°
E. Potential has no direction.
14. A 3.6 μC charge is moved from a position where its electric potential energy is 7.2 mJ to a position where
its potential energy is 1.8 mJ. What is the change in potential from the initial position to the final position?
A. 1500 V
B. 2000 V
C. -2000 V
D. 3500 V
E. -1500 V
16. A charge q1 is placed on the y-axis at y = 4.0 m and the resulting potential at the position (3.0 m, 4.0 m) is
3.0 V. The charge q1 is removed and a charge q2 is placed on the x-axis at x = 3.0 m and the resulting potential
at the position (3.0 m, 4.0 m) is 4.0 V. If both charges are in place simultaneously, what is the potential at (3.0
m, 4.0 m)?
A. 1.0 V
B. 3.5 V
C. 5.0 V
D. 7.0 V
E. 12 V
18. A hollow conducting sphere of radius 12 cm had a charge of 18 μC placed on it. What is the potential 20
cm from the center of the sphere?
A. 0 V
B. 15 V
C. 73 V
D. 8.1 × 105 V
E. 4.1 × 105 V
20. A hollow conducting sphere of radius 12 cm had a charge of 18 μC placed on it. What is the potential at the
center of the sphere?
A. 0 V
B. 24 V
C. 1.4 × 106 V
D. 1.6 × 106 V
E. infinite
22. A conducting sphere of radius 20 cm is charged so that the electric field reaches 3.0 × 105 V/m at its
surface. What is the potential at the surface of the sphere?
A. 3.0 × 104 V
B. 1.5 × 104 V
C. 4.5 × 104 V
D. 6.0 × 104 V
E. 2.7 × 105 V
23. A conducting sphere of radius 20 cm has a charge Q placed on it producing a field of magnitude E0 at its
surface. More charge is added to the surface until the magnitude of the field at the surface is 2 E0. How much
charge was added to the surface?
A. Q/2
B. Q
C. 2 Q
D. 1.4 Q
E. 3 Q
24. A conducting sphere of radius 20 cm has a charge Q placed on it producing a field of magnitude E0 at its
surface. More charge is added to the surface until the magnitude of the field at the surface is 2 E0. If the
potential at the surface was V0 when the field was E0, what is the potential when the field is 2 E0?
A. V0/2
B. 2 V0
C. 4 V0
D. 5 V0
E. 16 V0
27. Which of the following statements is true?
A. Electric field lines stay inside equipotent surfaces.
B. Equipotent surfaces intersect in straight lines.
C. Equipotent surfaces intersect in curved lines.
D. Electric field lines are perpendicular to equipotent surfaces.
E. Equipotent surfaces are parallel to each other.
29. Two large equipotent surfaces are flat and parallel and separated by a relatively small distance compared to
their size. One surface is at 25.0 V and the other is at 33.0 V. The surfaces are 1.25 cm apart. What is the
magnitude of the electric field midway between the surfaces?
A. 25.0 V/m
B. 29.0 V/m
C. 33.0 V/m
D. 6.40 × 102 V/m
E. 1.00 × 103 V/m
33. If electrons are accelerated from rest in an electron gun by sending them through a potential difference of
1000 V, what is the speed of the electrons?
A. 9.41 × 106 m/s
B. 1.33 × 106 m/s
C. 1.87 × 107 m/s
D. 1.97 × 106 m/s
E. 6.22 × 106 m/s
37. If helium nuclei and protons are each accelerated from rest through the same potential difference V, which
gets the greatest kinetic energy and by what factor is it greater?
A. The protons get twice as much kinetic energy.
B. The helium nuclei get twice as much kinetic energy.
C. They both get the same kinetic energy.
D. The protons get four times as much kinetic energy.
E. The helium nuclei get four times as much kinetic energy.
38. If helium nuclei and protons are each accelerated from rest through the same potential difference, how do
the resulting speeds compare?
A. The protons attain twice the speed of the helium nuclei.
B. The protons attain 1.4 times the speed of the helium nuclei.
C. The helium nuclei attain twice the speed of the protons.
D. The helium nuclei attain 1.4 times the speed of the protons.
E. They both attain the same speed.
40. A parallel plate capacitor has plates each of area 100 cm2 and with separation 0.25 mm. What is its
capacitance?
A. 40 nF
B. 0.35 nF
C. 4.4 μF
D. 88 pdf
E. 88 μF
41. A parallel plate capacitor has a paper dielectric having dielectric strength 8.0 kV/mm and dielectric constant
3.0. The plate area is 3000 cm2 and the plate separation is 0.50 mm. What is the capacitance?
A. 16 nF
B. 4.2 nF
C. 5.3 nF
D. 1.6 nF
E. 4.2 pdf
44. A parallel plate capacitor has an air dielectric. The capacitor is charged with surface charge density σ0 and
then the voltage source is removed. When an insulator with dielectric constant 5.0 is inserted between the
plates, what happens to the electric field strength if the surface charge density does not change?
A. It increases by a factor of 5.
B. It increases by a factor of 25.
C. It decreases by a factor of 5.
D. It decreases by a factor of 25.
E. It stays the same.
45. A parallel plate capacitor is attached to a voltage source providing 12 V. When an insulator of dielectric
constant 6.0 is then used to fill the air space between the capacitor plates, what happens to the surface charge
density on the plates if the voltage source is still attached?
A. It increases by a factor of 6.0.
B. It increases by a factor of 2.0.
C. It decreases by a factor of 6.0.
D. It decreases by a factor of 2.0.
E. It stays the same.
49. If the potential difference across the plates of a capacitor is doubled, what happens to the energy stored?
A. It stays the same.
B. It doubles.
C. It quadruples.
D. It halves.
E. It increases by a factor of 1.414.
51. To store 80 mJ of energy in a 100 μF capacitor, what voltage is necessary?
A. 10 V
B. 45 V
C. 4.0 V
D. 40 V
E. more than 120 V
53. The electric field in the dielectric between the plates of a capacitor is E. What is the charge density on the
A. E·V
B. E2ε0
C. V2·E
D. ε0E
E. κε0E
54. A parallel plate capacitor with an air dielectric is attached to a voltage source and charged. The voltage
source is removed, and then the plates are separated to double their previous distance. What happens to the
electric field between the plates when they are separated?
A. It doubles.
B. It quadruples.
C. It halves.
D. It is diminished by a factor of 4.
E. It stays the same.
56. A parallel plate capacitor with an air dielectric is attached to a voltage source and charged. The voltage
source is removed, and then the plates are separated to double their previous distance. What happens to the
energy stored by the capacitor when the plates are separated?
A. It doubles.
B. It quadruples.
C. It halves.
D. It is diminished by a factor of 4.
E. It stays the same.
57. What area plates would a parallel plate 1.0 F capacitor have with a plate separation of 0.10 mm and a
dielectric of constant 10?
A. 1000 cm2
B. 5500 cm2
C. 130 m2
D. 1.1 × 106 m2
E. 4.4 × 109 m2
59. If the plate area, plate separation, and dielectric constant all are doubled for a parallel plate capacitor, what
happens to the capacitance?
A. It stays the same.
B. It doubles.
C. It quadruples.
D. It halves.
E. It quarters.