Chapter 12: Electrostatic Phenomena
1. An electron situated near another electron would feel
A. a repulsive electrical force.
B. an attractive electrical force.
C. a repulsive magnetic force.
D. an attractive magnetic force.
E. no forces from the other electron.
Answer: A
2. Consider a proton and an electron placed near one another with no other objects close by.
They would
A. accelerate away from each other.
B. remain motionless.
C. accelerate toward each other.
D. be pulled together at constant speed.
E. move away from each other at constant speed.
Answer: C
3. Compared to the magnitude of the charge on a proton, the magnitude of the electrical charge
carried by an electron is
A. about the same.
B. exactly the same.
C. is only ½ as large.
D. is only ⅓ as large.
Answer: B
4. The charge of a proton is due to
A. physicists are not yet quite sure but explain charge as a property of the proton.
B. periodic pulsations of the surface of the proton.
C. the high density of the proton.
D. rapid spinning of the proton.
Answer: A
5. Two equal positive charges are near each other. If we increase the amount of charge on just
one of them, then
A. both charges feel an increased electrical force.
B. only smaller charge feels an increased electrical force.
C. the electric field felt by both charges increases.
D. the electric field felt by the smaller charge increases.
E. Both answers A and D
Answer: E
6. An atom has
A. just as many electrons as protons.
B. no neutrons in the nucleus.
C. more protons than electrons.
D. as many electrons as protons and neutrons combined.
E. at least 1 neutron.
Answer: A
7. A strip of fur is rubbed against a hard rubber rod. The rod thereby acquires a negative charge
because
A. frictional forces create electrons.
B. rubbing caused electrons to move from the fur to the rod.
C. friction caused protons to be removed from the rod.
D. electrons from the air molecules are transferred to the rod.
Answer: B
8. The electrical force between two charged objects depends on
A. the mass of the objects.
B. the color of the objects.
C. the amount of combined charge of both objects.
D. the amount of charge on each of the two objects.
E. which object has the greatest charge.
Answer: D
9. The electrical force between any two charged objects is
A. always attractive.
B. always repulsive.
C. always balanced by the action-reaction forces.
D. dependent on the sign of the charge on each object.
Answer: D
10. Our model for explaining the electrical interaction between charged objects
A. depends on the existence of three kinds of charge.
B. postulates that an electric field surrounds each charged object.
C. makes sense only at very high speeds.
D. depends very strongly on the mass of the two objects.
Answer: B
11. If the distance between two spherical charged objects increases by a factor of two, then the
electrical force between the objects
A. decreases by a factor of four.
B. is half as big.
C. does not change.
D. doubles.
E. increases by a factor of four.
Answer: A
12. The electric field created by a moving negative charge
A. points toward the charge.
B. points away from the charge.
C. describes concentric circles about the direction of motion.
D. points in the direction of motion.
E. points in the direction opposite to the velocity.
Answer: A
13. If the potential at point A is one volt it means that
A. an object at A has charge equal to one coulomb.
B. an electron at A can perform one joule of work.
C. there is a small battery present.
D. a charge at A has potential energy one joule for each coulomb of charge.
Answer: D
14. A metallic object has a net charge on it. For steady state conditions, the excess charge is
located
A. on the bottom of the object .
B. on the surface of the object.
C. near the side closest to the North magnetic pole.
D. at the center of mass of the object.
E. at the top of the object.
Answer: B
15. After a glass rod is rubbed with a nylon cloth
A. the rod will have a positive charge and the cloth negative.
B. both the rod and cloth will have a positive charge.
C. the rod will have a negative charge and the cloth positive.
D. both the rod and cloth will have a negative charge.
E. the rod will have a negative charge and the cloth will be neutral.
Answer: A
16. A rubber rod is rubbed with fur, so that the fur becomes positive. The rod is then used to
charge an electroscope. The charge on the electroscope will be
A. positive if charged by contact.
B. positive if charged by induction.
C. neutral.
D. negative if charged by induction.
Answer: B
17. A positively charged rod is brought close to an uncharged electroscope. While the rod is
close, one’s finger touches the far side of the metal ball on the electroscope. The finger is
removed and then the rod is taken away. The electroscope is
A. positively charged.
B. negatively charged.
C. uncharged.
Answer: B
18. A negatively charged rod is brought close to an uncharged electroscope. While the rod is
close one’s finger touches the far side of the metal ball on the electroscope. After the charged
rod has been removed the finger is removed. The electroscope is
A. positively charged.
B. negatively charged.
C. uncharged.
Answer: C
19. Comparing the electrostatic force and the gravitational force we can say that
A. both have the same dependence on distance, both involve attraction and repulsion but the
gravitational force is stronger.
B. both have the same dependence on distance, both involve attraction and repulsion but the
electrostatic force is stronger.
C. both have the same dependence on distance, the electrostatic force can be either attractive or
repulsive while the gravitational force is only repulsive, and the electrostatic force is weaker.
D. both have the same dependence on distance, the electrostatic force can be either attractive or
repulsive while the gravitational force is only attractive, and the electrostatic force is stronger.
E. the electrostatic force falls off more rapidly with distance, the electrostatic force can be either
attractive or repulsive while gravitation is only attractive and the electrostatic force is stronger.
Answer: D
20. A 10 µC charge is at the origin. A -5 µC charge is on the x-axis 10 cm to the right of the
origin. At what point other than at infinity can a 1 µC charge be placed so that there will be no
net electrostatic force on it?
A. At one point between the two charges.
B. At one point on the x-axis to the right of the negative charge.
C. At one point on the x-axis to the left of positive charge.
D. At some point off the x-axis either above or below.
E. At no point.
Answer: B
21. Two equal charges repel one another with a force of 4.0 × 10-4 N when they are 10 cm apart.
If they are moved until the separation is 5.0 cm, the repulsive force will be
A. 16.0 × 10-4N.
B. 8.0 × 10-4N.
C. 4.0 × 10-4N.
D. 2.0 × 10-4N.
E. 1.0 × 10-4N.
Answer: A
22. A positive charge is fixed at the origin. A negative charge is moved along the x-axis from
x = 50 cm to x = 10 cm. The potential energy of the negative charge
A. does not change.
B. increases.
C. decreases.
Answer: C
23. Imagine four equal positive charges, q, placed on points of a circle of radius r at the 3, 6, 9
and 12 o’clock positions. The magnitude of the electric field at the center of the circle is given
by
A. 4kq/r.
B. 4kq/r2.
C. kq/r.
D. kq/r2.
E. zero.
Answer: E
24. Three equal negative charges are placed at three of the four corners of a square. The
direction of the electric field at the remaining corner of the square is
A. along a side of the square toward one of the charges.
B. along a side of the square away from one of the charges.
C. along the diagonal connecting this corner and another charge, away from the other charge.
D. along the diagonal connecting this corner and another charge, toward the other charge.
E. no direction, zero field.
Answer: D
25. A uniform electric field has a magnitude of 10 N/C and is directed upward. A charge
brought into the field experiences a force of 5.0 N downward. The charge must be
A. +50 C.
B. -50 C.
C. +0.5 C.
D. -0.5 C.
E. -2.0 C.
Answer: D
26. A capacitor consisting of two parallel plates separated by 2.0 cm has a potential of 100 V on
the top plate and a potential of 0 V on the bottom plate. The value of the electric field in the
middle is
A. 5.0 N/C.
B. 50 N/C.
C. 500 N/C.
D. 5000 N/C.
E. 200 N/C.
Answer: D
27. A capacitor consisting of two separated parallel horizontal plates has a uniform electric field
directed upward. If a negative charge is placed exactly midway between the two plates, it will
A. remain at rest.
B. be accelerated upward.
C. be accelerated downward.
D. be accelerated to the right.
E. be accelerated to the left.
Answer: C
28. The unit for electric field, N/C can be written equivalently as
A. V.
B. m/V.
C. V/C.
D. C/V.
E. V/m.
Answer: E
29. A plastic rod is rubber with fur. The rod is then touched to the metal knob of an
electroscope. The sign of the charge on the electroscope after contact is ___________________.
Answer: negative
30. A glass rod is rubbed with nylon. The rod is then brought close to the metal knob of an
electroscope. A person’s finger briefly touches the knob on the far side and is then removed.
After the rod is removed the charge on the electroscope will be _________.
Answer: negative
31. A positive test charge is moved closer to another positive charge. The potential of the test
charge _____________________ (indicate change).
Answer: increases
32. It is observed that a positive charge released between the parallel plates of a capacitor moves
upward. The direction of the electric field between the capacitor plates is __________________.
Answer: upward
33. A negative charge released between the parallel plates of a capacitor moves downward. The
potential energy of the negative charge _________________________ (indicate change).
Answer: decreases
34. In a certain region the electric lines of force get farther apart as one moves to the right. The
force on a positive charge will decrease as the charge is moved to the ____________________.
Answer: right
35. Four equal positive charges are placed at the corners of a square. The force on a +1 C
charge placed at the center due to any single charge is 10 N. The value of the electric field at the
center due to all charges is ____________________ N/C.
Answer: zero
36. A small bit of paper is electrically neutral. A charged rod can attract the bit of paper by the
process of __________________.
Answer: polarization