Question 1

The magnitude of the force on a proton sitting midway between a pair of parallel conducting plates that are at potentials of −17 V and 55 V, respectively, is 7.69 × 10−16 N. What is the separation distance between the plates?

Accepted Answer

A)  3.0 cm 
B)  1.2 cm 
C)  0.58 cm 
D)  1.5 cm

Question 2

The electric potential at a distance d from a point charge is V. At a distance d', the potential is 2V. What is the ratio of electric field at d' to that at d?

Accepted Answer

A)  4 
B)  more information is necessary 
C)  2 
D)  1/2 
E)  1/4

Question 3

A hollow conducting sphere of radius 12 cm has a net charge of 18 μC. What is the potential at the center of the sphere?

Accepted Answer

A)  0 V 
B)  24 V 
C)  1.3 × 106 V 
D)  1.6 × 106 V 
E)  infinite

Question 4

A helium nucleus is accelerated from rest through a potential difference V to a kinetic energy of 3.2 × 10−13 J. What is V?

Accepted Answer

A)  1.0 MV 
B)  2.0 MV 
C)  1.6 MV 
D)  3.2 MV 
E)  0.51 MV

Question 5

A parallel plate capacitor has a dielectric with constant 3.5. The plates are circular with radius 0.07 m, and the separation gap is 0.375 mm. What energy may be stored in this capacitor if 1250 V is the applied voltage?

Accepted Answer

A)  9.9 × 10−4 J 
B)  2.8 × 10−4 J 
C)  2.0 × 10−3 J 
D)  3.5 × 10−3 J

Question 6

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?

Accepted Answer

A)  q1 
B)  0.5 q1 
C)  −0.5 q1 
D)  (q1 + q2)/2 
E)  no value will have this result

Question 7

A parallel plate capacitor is charged to 12 V and the voltage source is then disconnected. When the air space between the plates is then filled with a dielectric of constant 6.0, what is the resulting voltage between the plates?

Accepted Answer

A)  72 V 
B)  12 V 
C)  6.0 V 
D)  2.0 V 
E)  none of these choices are correct

Question 8

If the plate area, plate separation, and dielectric constant all are doubled for a parallel plate capacitor, what happens to the capacitance?

Accepted Answer

A)  It stays the same. 
B)  It doubles. 
C)  It quadruples. 
D)  It halves. 
E)  It quarters.

Question 9

The SI unit for electric potential energy is equivalent to

Accepted Answer

A)  N·m2. 
B)  V·C. 
C)  N/m. 
D)  C·m2. 
E)  none of these choices are correct

Question 10

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?

Accepted Answer

A)  Q/2 
B)  Q 
C)  2 Q 
D)  1.4 Q 
E)  3 Q

Question 11

A parallel plate capacitor has a paper dielectric having dielectric strength 8.00 kV/mm and dielectric constant 3.00. The plate area is 3000 cm2 and the plate separation is 0.500 mm. If 10.0 V are applied to this capacitor, what is the charge on the capacitor?

Accepted Answer

A)  50.0 μC 
B)  42.0 nC 
C)  159 nC 
D)  16.0 nC 
E)  42.0 μC

Question 12

If two equipotent planes differ in potential by 1.0 volt, and the electric field between them is 20 N/C, what is the separation of the planes?

Accepted Answer

A)  20 cm 
B)  0.050 cm 
C)  5.0 cm 
D)  2.0 cm 
E)  4.0 cm

Question 13

An air-filled 3.0 nF capacitor is charged to 8.0 V. If the plate separation is 100 μm, what is the energy density in the electric field between the plates?

Accepted Answer

A)  57 J/m3 
B)  280 J/m3 
C)  57 mJ/m3 
D)  28 mJ/m3 
E)  more than 100 J/m3

Question 14

The electric field between two charged plates is 7.2 kN/C. If the plates are separated by 3.0 mm, what is the potential difference between them?

Accepted Answer

A)  Need more information 
B)  240 kV 
C)  220 V 
D)  22 V

Question 15

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 potential at the first position?

Accepted Answer

A)  1500 V 
B)  2000 V 
C)  −2000 V 
D)  3500 V 
E)  −1500 V

Question 16

A 2.00 nC charge is placed on the x-axis at x = −3.00 cm, another 2.00 nC charge is placed on the x-axis at x = 3.00 cm, and a third 2.00 nC charge is placed on the y-axis at y = 3.00 cm. What is the potential at the origin?

Accepted Answer

A)  1800 V 
B)  2700 V 
C)  3600 V 
D)  5400 V 
E)  108 V

Question 17

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 highest voltage that can be applied to this capacitor before breakdown occurs?

Accepted Answer

A)  15 V 
B)  1.2 × 102 V 
C)  4.0 × 102 V 
D)  4.0 × 103V 
E)  1.2 × 104 V

Question 18

A conducting sphere of radius 20 cm is charged to a potential of 1.0 × 106 volts. What is the charge on its surface?

Accepted Answer

A)  22 μC 
B)  4.4 μC 
C)  4.7 mC 
D)  9.0 nC 
E)  16 mC

Question 19

An air-filled parallel plate capacitor 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 in the capacitor when the plates are separated?

Accepted Answer

A)  It doubles. 
B)  It quadruples. 
C)  It halves. 
D)  It is diminished by a factor of 4. 
E)  It stays the same.

Question 20

Which of the following unit equations is correct?

Accepted Answer

A)  N·C = V/m 
B)  N·m = V·C 
C)  N·V = N·m 
D)  N/m = V/C 
E)  N/V = m/C

Exam 17: Electric Potential

The magnitude of the force on a proton sitting midway between a pair of parallel conducting plates that are at potentials of −17 V and 55 V, respectively, is 7.69 × 10⁻¹⁶ N. What is the separation distance between the plates?

The electric potential at a distance d from a point charge is V. At a distance d', the potential is 2V. What is the ratio of electric field at d' to that at d?

A hollow conducting sphere of radius 12 cm has a net charge of 18 μC. What is the potential at the center of the sphere?

A helium nucleus is accelerated from rest through a potential difference V to a kinetic energy of 3.2 × 10⁻¹³ J. What is V?

A parallel plate capacitor has a dielectric with constant 3.5. The plates are circular with radius 0.07 m, and the separation gap is 0.375 mm. What energy may be stored in this capacitor if 1250 V is the applied voltage?

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?