Deck 15: Electric Charge, Forces, and Fields

Question 1

State the charge-force law.

Answer 1

Like charges repel, and unlike charges attract.

Question 2

State the principle of conservation of charge.

Answer 2

The net charge of an isolated system remains constant.

Question 3

What does it mean to say something (for example charge) is "quantized"?

Answer 3

A "quantized" something comes in basic units and occurs as an integer number of these basic units. For example, isolated objects will be found to have a charge plus or minus ne where n is an integer and e = 1.6 × 10^-19 Coulombs.

Question 4

Explain how objects can get charged by FRICTION.

Question 5

State the underlying physical principle of Gauss's Law.

Question 6

The coulomb, which is the unit of charge, is the charge on one electron.

Question 7

Electrons carry a

A) negative charge.
B) variable charge.
C) positive charge.
D) neutral charge.

Question 8

A quark can have a charge of

A) e/2.
B) -1/3 e.
C) -3/2 e.
D) e/4.

Question 9

When an electron is removed from a neutral atom, it becomes

A) a negative ion.
B) more massive.
C) a positive ion.
D) heavier.
E) a bipolar atom.

Question 10

A glass rod is rubbed with a piece of silk. During the process the glass rod acquires a positive charge and the silk

A) acquires a positive charge also.
B) could either be positively charged or negatively charged. It depends on how hard the rod was rubbed.
C) acquires a negative charge.
D) remains neutral.

Question 11

Two charged objects attract each other with a certain force. If the charges on both objects are doubled with no change in separation, the force between them

A) halves.
B) increases, but we can't say how much without knowing the distance between them.
C) becomes zero.
D) doubles.
E) quadruples.

Question 12

An electron and a proton are separated by a distance of 1 m. What happens to the size of the force on the proton if the electron is moved 0.5 m closer to the proton?

A) It decreases to one-fourth its original value.
B) It decreases to one-half its original value.
C) It increases to 4 times its original value.
D) It increases to 2 times its original value.
E) It increases to 8 times its original value.

Question 13

Sphere A carries a net charge and sphere B is neutral. They are placed near each other on an insulated table. Which statement best describes the electrostatic force between them?

A) There is no force between them since one is neutral.
B) The force is attractive if A is charged positively and repulsive if A is charged negatively.
C) There is a force of repulsion between them.
D) There is a force of attraction between them.

Question 14

A point charge of +Q is placed at the centroid of an equilateral triangle, as shown in Figure 15-1. When a second charge of +Q is placed at one of the triangle's vertices, an electrostatic force of 4 N acts on it.

What is the magnitude of the force that acts on the center charge when a third charge of +Q is placed at one of the other vertices?

A) zero
B) 8 N
C) 16 N
D) 4 N

Question 15

In electricity, what quantity is analogous to the "acceleration of gravity" g (which is a force per unit mass)?

A) an electric dipole
B) electric charge
C) electric force
D) electric potential
E) electric field

Question 16

Electric dipoles always consist of two charges that are

A) equal in magnitude; opposite in sign.
B) equal in magnitude; both are positive.
C) equal in magnitude; both are negative.
D) unequal in magnitude; opposite in sign.

Question 17

An electric dipole placed into a uniform electric field feels a net force

A) of zero magnitude.
B) along the field.
C) perpendicular to the field.
D) opposite the field.

Question 18

Which of the following makes an approximate uniform electric field?

A) a metal charged cylinder
B) very large, closely separated, parallel oppositely charged plates
C) two long parallel, closely separated, oppositely charged lines of charge
D) a very long line of positive charge

Question 19

Electric field lines

A) are closer together the stronger the field.
B) start on negative charges and end on positive charges.
C) were invented by Isaac Newton.
D) were discovered by Franklin.
E) are perpendicular to the lines of force.

Question 20

The electric field shown in Figure 15-3

A) increases to the right.
B) is uniform.
C) increases down.
D) decreases to the right.
E) decreases down.

Question 21

An electric dipole placed into a non-uniform electric field feels a net force

A) parallel to the field.
B) of zero magnitude.
C) 45° with respect to the field.
D) perpendicular to the field.

Question 22

Two stationary point charges q₁ and q₂ are shown in Figure 15-4 the sketch along with some electric field lines representing the field between them.

What can you deduce from the sketch?

A) q₁is negative and q₂ is positive; the magnitudes are equal.
B) q₁and q₂ have the same sign; the magnitudes are equal.
C) q₁is positive and q₂ is negative; the magnitude of q₁ is greater than the magnitude of q₂.
D) q₁is positive and q₂ is negative; the magnitude of q₁ is less than the magnitude of q₂.
E) q₁and q₂ have the same sign; the magnitude of q₁ is greater than the magnitude of q₂.

Question 23

The electric field at the surface of a conductor is

A) parallel to the surface.
B) never zero.
C) perpendicular to the surface.
D) always zero.

Question 24

Several electrons are placed on a hollow metal sphere. They

A) clump together on the sphere's outer surface.
B) become uniformly distributed on the sphere's outer surface.
C) become uniformly distributed on the sphere's inner surface.
D) clump together on the sphere's inner surface.

Question 25

A solid block of metal is placed in a uniform electric field. Which statement is correct concerning the electric field in the block's interior?

A) The interior field points in a direction opposite to the exterior field.
B) The interior field points in a direction that is at right angles to the exterior field.
C) The interior field points in a direction that is parallel to the exterior field.
D) There is no electric field in the block's interior.

Question 26

If a solid metal sphere and a hollow metal sphere of equal diameters are each given the same charge, the electric field (E) midway between the sphere center and the surface is

A) zero for both.
B) greater for the solid sphere than for the hollow sphere.
C) greater for the hollow sphere than for the solid sphere.
D) equal in magnitude for both, but one is opposite in direction from the other.

Question 27

To be more effective, how should one shape the tip of a lightning rod?

A) sharpened to a point
B) flat (cut off perpendicular to the rod axis)
C) with a rounded tip (hemispherical)

Question 28

Which of the following is an accurate statement?

A) If a solid metal sphere carries a net charge, the charge will be uniformly distributed throughout the volume of the sphere.
B) The electric field at the surface of a conductor is not necessarily perpendicular to the surface in all cases.
C) If a solid metal sphere carries a net charge, the charge will move to the sphere surface.
D) A conductor cannot carry a net charge.

Question 29

The statement that "the number of field lines passing through a surface is proportional to the net charge enclosed" is known as

A) Franklin's Law.
B) Coulomb's Law.
C) Gauss's Law.
D) The Law of Enclosure.
E) Faraday's Law.

Question 30

-Figure 15-5 shows four Gaussian surfaces surrounding a distribution of charges. Which Gaussian surfaces have an electric flux of +q/ _o through them?

A) a.
B) b.
C) b and c.
D) c.
E) b and d.

Question 31

-Figure 15-5 shows four Gaussian surfaces surrounding a distribution of charges. Which Gaussian surfaces have no electric flux through them?

A) a.
B) b.
C) b and d.
D) b and c.
E) c.

Question 32

Consider the x-axis with 4.0 μC at x = 1.0 meter and -2.0 μC at the origin. Where should 6.0 μC be placed so that the net force on it is zero?

Question 33

Two volleyballs, each of mass 0.300 kg, are charged by an electrostatic generator. Each is attached to an identical string and suspended from the same point, as shown in Figure 15-6. They repel each other and hang with separation 50.0 cm. The length of the string from the point of support to the center of a ball is 250. cm.

Determine the charge on each ball.

Question 34

Consider a container of 2.0 grams of hydrogen (one gram mole) Suppose you removed all the electrons and moved them to the other side of the Earth (Earth diameter 12740. Km).
(a) How much charge is left behind?
(b) What is the attractive force between the protons here and the electrons at the other side of the Earth?

Question 35

Charge +2q is placed at the origin and charge -q is placed at x = 2a. Where can a third positive charge +q be placed so that the force on it is zero?

Question 36

A proton and electron are separated by 3.5 nm.
(a) What is the magnitude of the force on the electron?
(b) What is the magnitude of the force on the proton?
(c) What is the electric field of the proton at the electron position?

Question 37

The charge carried by one electron is e = -1.6 × 10^-19 C. The number of excess electrons necessary to produce a charge of 1.0 C is

A) 6.3 × 10⁶.
B) 1.6 × 10¹⁸.
C) 1.6 × 10¹⁹.
D) 6.3 × 10⁹.
E) 6.3 × 10¹⁸.

Question 38

A piece of plastic has a net charge of +2.00 $\mu$ C. How many more protons than electrons does this piece of plastic have?

A) 2.50 × 10¹³
B) 2.50 × 10¹⁹
C) 1.25 × 10¹³
D) 1.25 × 10¹⁹
E) 0

Question 39

Two point charges of magnitudes + 8.00 $\mu$ C, and + 10.0 $\mu$ C are placed along the x-axis at x = 0 cm and x = 100 cm, respectively. Where must a third charge be placed along the x-axis so that it does not experience any net force because of the other two charges?

A) 47.2 cm
B) 50 cm
C) 91.2 cm
D) 9.12 cm
E) 4.72 cm

Question 40

Two point charges of magnitude + 4.00 $\mu$ C and - 6.00 $\mu$ C are placed along the x-axis at x = 0 cm and x = 40.0 cm, respectively. Where must a third charge, q, be placed along the x-axis so that it does not experience any net force because of the other two charges?

A) 0.200 m
B) 0.180 m
C) - 0.180 m
D) - 1.78 m
E) 1.78 m

Question 41

A metal sphere of radius 2.0 cm carries a charge of 3.0 $\mu$ C. What is the electric field 6.0 cm from the center of the sphere?

A) 5.7 × 10⁶ N/C
B) 4.2 × 10⁶ N/C
C) 9.3 × 10⁶ N/C
D) 6.4 × 10⁶ N/C
E) 7.5 × 10⁶ N/C

Question 42

Consider point charges of +Q and +4Q, which are separated by 3 m. At what point, on a line between the two charges, would it be possible to place a charge of -Q such that the electrostatic force acting on it would be zero?

A) 1 m from the +4 charge
B) 3 m from the +4 charge
C) There is no such point possible.
D) 1 m from the +Q charge
E) 3/5 m from the +Q charge

Question 43

A force of 10 N acts on a charge of 5.0 $\mu$ C when it is placed in a uniform electric field. What is the magnitude of this electric field?

A) 0.50 MN/C
B) 1.0 MN/C
C) 1000 MN/C
D) 2.0 MN/C
E) 50 MN/C

Question 44

A point charge of +Q is placed at the center of a square, and a second point charge of -Q is placed at the upper-left corner. It is observed that an electrostatic force of 2 N acts on the positive charge at the center.

What is the magnitude of the force that acts on the center charge if a third charge of -Q is placed at the lower-left corner?

A) 2 N
B) 2/ N
C) zero
D) 4 N

Question 45

Two point charges of + 30.0 $\mu$ C and - 9.00 $\mu$ C are separated by a distance of 20.0 cm. A +7.00 $\mu$ C charge is placed midway between these two charges. What is the electric force acting on this charge because of the other two charges?

A) 2.45 N directed towards the positive charge
B) 0.453 N directed towards the negative charge
C) 245 N directed towards the positive charge
D) 245 N directed towards the negative charge
E) 2.45 N directed towards the negative charge

Question 46

Two point charges of + 6.00 $\mu$ C and + 9.00 $\mu$ C are placed inside a cube of edge length 0.100 m. The net electric flux due to these charges is given by

A) 1.69 × 10⁶ Nm²/C
B) 4.20 × 10⁶ Nm² /C
C) 0.450 × 10⁶ Nm²/C
D) 3.80 × 10⁶ Nm²/C
E) 0.340 × 10⁶ Nm²/C