Deck 12: Electrostatic Phenomena

Question 1

An electron situated near another electron would feel

A) an attractive magnetic force.
B) an attractive electrical force.
C) a repulsive magnetic force.
D) a repulsive electrical force.
E) no forces from the other electron.

Answer 1

a repulsive electrical force.

Question 2

After a glass rod is rubbed with a nylon cloth

A) both the rod and cloth will have a positive charge.
B) the rod will have a positive charge and the cloth negative.
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 2

the rod will have a positive charge and the cloth negative.

Question 3

The charge of a proton is due to

A) rapid spinning of the proton.
B) periodic pulsations of the surface of the proton.
C) the high density of the proton.
D) reasons physicists are not yet quite sure of, but they explain charge as a property of the proton.

Answer 3

reasons physicists are not yet quite sure of, but they explain charge as a property of the proton.

Question 4

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) negatively charged.
B) positively charged.
C) uncharged.

Question 5

Compared to the magnitude of the charge on a proton, the magnitude of the electrical charge carried by an electron is

A) exactly the same.
B) about the same.
C) only 1/2 as large.
D) only 1/3 as large.

Question 6

A typical, neutrally charged 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.

Question 7

Two equal positive charges are near each other. If we increase the amount of charge on just one of them, then

A) the electric field points toward the larger charge.
B) the strength of the electrical force on both decreases.
C) the electric field at the position of the smaller charge increases.
D) the larger charge feels a stronger electrical force and the other a weaker electrical force.

Question 8

Our model for explaining the electrical interaction between charged objects

A) postulates that an electric field surrounds each charged object.
B) makes sense only at very high speeds.
C) depends on the existence of three kinds of charge.
D) depends very strongly on the mass of the two objects.

Question 9

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) negative if charged by polarization.
B) positive if charged by contact.
C) negative if charged by induction.
D) positive if charged by induction.
E) neutral.

Question 10

A 10 µC charge is at the origin. A -15 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 on the x-axis to the left of the positive charge.
B) At some point off the x-axis either above or below.
C) At one point between the two charges.
D) At one point on the x-axis to the right of the negative charge.
E) At no point.

Question 11

The electric field created by a moving negative charge

A) points away from the charge.
B) describes concentric circles about the direction of motion.
C) points in the direction of motion.
D) points in the direction opposite to the velocity.
E) points toward the charge.

Question 12

The electrical force between any two charged objects is

A) always attractive.
B) always repulsive.
C) dependent on the sign of the charge on each object.
D) always balanced by the action-reaction forces.

Question 13

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 electro?static force can be either attractive or repulsive while the gravitational force is only attractive, and the electrostatic force is stronger.
D) 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.
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.

Question 14

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) negatively charged.
B) positively charged.
C) uncharged.

Question 15

A metallic object has a net charge on it. For steady state conditions, the excess charge is

A) spread evenly throughout the object.
B) in the center of the object.
C) only on the surface.
D) on the bottom of the object.
E) on the north side of the object.

Question 16

The electrical force between two charged objects depends on

A) the number of electrons in the objects.
B) the total number of protons in both objects.
C) the sum of the net charges on the objects.
D) the product of the net charge on each of the two objects.
E) just the magnitude of the largest charge.

Question 17

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) accelerate toward each other.
C) remain motionless.
D) be pulled together at constant speed.
E) move away from each other at constant speed.

Question 18

If the potential at point A is one volt it means that

A) a charge at A has potential energy one joule for each coulomb of charge.
B) an object at A has charge equal to one coulomb.
C) an electron at A can perform one Joule of work.
D) there is a small battery present.

Question 19

A strip of fur is rubbed against a hard rubber rod. The rod thereby acquires a negative charge because

A) electrons from the air molecules are transferred to the rod.
B) frictional forces create electrons.
C) rubbing caused electrons to move from the fur to the rod.
D) friction caused protons to be removed from the rod.

Question 20

If the distance between two spherical charged objects decreases by a factor of two, then the electrical force between the objects

A) decreases by a factor of four.
B) increases by a factor of four.
C) is half as big.
D) doubles.
E) does not change.

Question 21

Consider the field lines of the electric dipole in this diagram, relative to the w-axis and the z-axis. In which direction does the electric field point where the two axes intersect?

A) 45 $\degree$ up and to the right, parallel to the z-axis:
B) 45 $\degree$ down and to the right, parallel to the w-axis:
C) 45 $\degree$ down and to the left, parallel to the z-axis:
D) 45 $\degree$ up and to the left, parallel to the w-axis:

Question 22

Consider the horizontal parallel plates. The upper plate has a voltage difference of 30 V with the lower plate, and they are separated by 3 cm. You move the two plates carefully to a separation of 4 cm. What is the strength of the electric field between the plates?

A) 3000 volts/meter
B) 1000 volts/meter
C) 750 volts/meter
D) 7.5 volts/meter

Question 23

Two charges are shown below. What is the direction of the electric field at the indicated point?

A) A
B) B
C) C
D) D
E) E

Question 24

The most common form of lightning strike from a cloud to the ground involves negative charge moving from the cloud to the ground. Just before a lightning strike,

A) the electric field must point toward the sky.
B) the potential energy of the electrons in the cloud must be small.
C) the potential must be larger near the cloud.
D) there are no charges on the ground.

Question 25

Two charges of equal magnitude but opposite sign are 10 cm apart. The potential is largest

A) halfway between the two charges.
B) close to the positive charge.
C) close to the negative charge.
D) far away from the two charges.

Question 26

As a given thundercloud's base elevation gets lower and lower, the possibility of lightning strike

A) is greater, because the electric field strength increases.
B) is less, since the electric field gets weaker.
C) is unchanged, because the thundercloud has not polarized.

Question 27

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) decreases.
C) increases.

Question 28

If the plates of a charged parallel plate capacitor were moved further apart, the potential energy of each of the charges on the capacitor would

A) remain the same.
B) increase.
C) decrease.
D) increase or decrease depending on the initial plate separation.

Question 29

If two metal balls each have a charge of -10^-6 C and the repulsive force between them is 1 N, how far apart are they? (Coulomb's constant is k=9.0 $\times$ 10⁹ N^.m²/C².)

A) 9.5 m
B) 9.0 mm
C) 9.5 cm
D) 0.9 m

Question 30

Two equal charges repel one another with a force of 4.0 $\times$ 10^-4 N when they are 10 cm apart. (Coulomb's constant is k=9.0 $\times$ 10⁹ N^.m²/C².) If they are moved until the separation is 5 cm, the repulsive force will be

A) 0.25 $\times$ 10^-4 N.
B) 1.0 $\times$ 10^-4 N.
C) 4.0 $\times$ 10^-4 N.
D) 16 $\times$ 10^-4 N.
E) 64 $\times$ 10^-4 N.

Question 31

When you shuffle your feet on a carpet on a dry day, you can accumulate a charge. The fact that you accumulate a charge means that the carpet is

A) an insulator, because if it weren't, the charge would immediately leave you.
B) an insulator, because only insulators can be charged by contact.
C) a conductor, because charge cannot leave an insulator and move to you.
D) a conductor, because conductors always have extra electrons.

Question 32

Refer to the dipole in the z, w coordinate system above. Consider the electric field at a point $\degree$ out on the z-axis, above and to the right of the intersection of the axes. In which direction does the electric field point at point $\degree$ ?

A) 45 $\degree$ down and to the right, parallel to the w-axis:
B) 45 $\degree$ up and to the right, parallel to the z-axis:
C) 45 $\degree$ up and to the left, parallel to the w-axis:
D) 45 $\degree$ down and to the left, parallel to the z-axis:

Question 33

You have a pair of horizontal parallel plates, with the positive plate above and the negative plate below. How will the lines of constant potential be arranged in this perspective?

A) Spherically, since all charges are either electrons or protons.
B) Horizontally.
C) Vertically.

Question 34

The unit for electric field, N/C, can be written equivalently as

A) V/m.
B) C/V.
C) V/C.
D) m/V.
E) V.

Question 35

A point charge creates the electric field shown. At which of the points would the potential energy of a positive test charge have the largest value?

A) A
B) B
C) C
D) D

Question 36

A charged comb attracts bits of neutral dust in the air. This happens because

A) the dust becomes polarized.
B) the dust grounds the comb.
C) the dust becomes charged by induction.
D) the dust is a good conductor.

Question 37

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) be accelerated upward.
B) be accelerated downward.
C) remain at rest.
D) be accelerated to the right.
E) be accelerated to the left.

Question 38

A capacitor consisting of two parallel plates separated by 2.0 cm has a potential of 40 V on the top plate and a potential of 0 V on the bottom plate. The electric field in the middle is

A) 2000 N/C, downward.
B) 80 N/C, upward.
C) 40 N/C, downward.
D) 20 N/C, upward.

Question 39

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. Coulomb's constant is k. The magnitude of the electric field at the center of the circle is given by

A) 4 kq/r.
B) 4 kq/r².
C) kq/r.
D) kq/r².
E) zero.

Question 40

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 line connecting this corner with the opposite corner, and toward that corner.
D) along the line connecting this corner with the opposite corner, but away from that corner.
E) no direction, zero field.

Question 41

A drop of water dripping from the faucet in your kitchen is electrically neutral. A charged plastic hair comb can attract the drips and drops by the process of __________________.

Question 42

A positive test charge is moved closer to a negative charge. The potential of the test charge _____________________ (indicate whether it increases, decreases, or stays the same).

Question 43

If a charge of -3 x 10^-6 C were allowed to fall through a potential difference of +500 V, the change in potential energy for the charge would be

A) -1.5 $\times$ 10^-4 Joules
B) 1.5 $\times$ 10^-4 Joules
C) -1.5 $\times$ 10^-3 Joules
D) 1.5 $\times$ 10^-3 Joules

Question 44

Negative charges feel a force __________ (indicate direction) values of higher electric potentials.

Question 45

A plastic rod is rubbed 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 ___________________.

Question 46

Electrical force per unit charge is known as the _______________________

Question 47

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 _________.

Question 48

Two very small spherical metal objects, each with 1 Coulomb of charge, are brought together in a vacuum so that the separation distance between their centers is 1 mm. What is the force of repulsion between the two object? (Coulomb's constant is k=9.0 $\times$ 10⁹ N^.m²/C².)

A) 9 $\times$ 10¹² N
B) 9 $\times$ 10¹³ N
C) 9 $\times$ 10¹⁴ N
D) 9 $\times$ 10¹⁵ N

Question 49

If a negatively charged rod is brought close to (but not touching) an initially neutral object, the object becomes polarized and has ___________ charge.

Question 50

A device used by Charles Coulomb to measure the presence or absence of electric charge is called a(n) _____________________________

Question 51

In a certain region of space, lines of constant positive electric potential get farther apart as one moves to the right. The force on a negative charge in this region will point to the ____________________.

Question 52

A negatively charged grain of soot released between the parallel plates of a capacitor moves leftward. The potential between the parallel plates _________ (indicate whether it increases, decreases, or stays the same) from right to left, and the potential energy of the negatively charged grain of soot _________________________ (indicate whether it increases, decreases, or stays the same) from right to left.

Question 53

To bring a negative charge from an infinitely great distance away into the presence of a positive charge would require a ____________________ amount of work to be done.

A) positive
B) negative
C) zero
Fill in the Blank Questions

Question 54

The change in electrical potential energy per unit of charge that is moved from one place to another is known as ________________________

Question 55

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.

Question 56

It is observed that a negatively charged grain of soot released between the parallel plates of a capacitor moves leftward. The direction of the electric field between the capacitor plates is __________________.

Question 57

Electrostatic precipitators can effectively remove most of which of the following air pollutants from a smoke stack

A) sulfur dioxide
B) carbon monoxide
C) nitrous oxides
D) particulates