Deck 21: Electric Charge and Electric Field

Question 1

A positive charge placed in an electric field experiences a force in the direction of the field.

Answer 1

True

Question 2

A negatively charged rod is brought near one end of an uncharged metal bar. The end of the metal bar farthest from the charged rod will be charged

A)positive.
B)negative.
C)neutral.
D)none of the given answers

Answer 2

negative.

Question 3

If an atom has become a positive ion, it has

A)gained an electron or electrons.
B)lost an electron or electrons.
C)gained a proton or protons.
D)gained a proton and an electron.
E)lost a proton or protons.

Answer 3

lost an electron or electrons.

Question 4

If a conductor is placed in an electric field under electrostatic conditions, the electric field is excluded from the inside of the conductor.

Question 5

A material is a good conductor because it

A)has numerous free electrons.
B)has unattached protons.
C)is not an insulator.
D)is an insulator.
E)is a metal.

Question 6

Materials in which the electrons are bound very loosely to the nuclei and can move about freely within the material are referred to as

A)insulators.
B)conductors.
C)semiconductors.
D)superconductors.
E)polar.

Question 7

If an electroscope is charged by induction

A)nothing will happen since electroscopes require being charged by conduction.
B)it will acquire a negative charge.
C)its leaves will separate because of the interaction of the charges.
D)its leaves will remain attached.
E)it will acquire a positive charge.

Question 8

An originally neutral electroscope is briefly touched with a positively charged glass rod. The electroscope

A)remains neutral.
B)becomes negatively charged.
C)becomes positively charged.
D)could become either positively or negatively charged, depending on the time of contact.

Question 9

An originally neutral electroscope is grounded briefly while a positively charged glass rod is held near it. After the glass rod is removed, the electroscope

A)remains neutral.
B)is negatively charged.
C)is positively charged.
D)could be either positively or negatively charged, depending on how long the contact with ground lasted.

Question 10

A neutral atom always has

A)more neutrons than protons.
B)more neutrons than electrons.
C)more protons than electrons.
D)the same number of neutrons as protons.
E)the same number of protons as electrons.

Question 11

A positive object touches a neutral electroscope, and the leaves separate. Then a negative object is brought near the electroscope, but does not touch it. What happens to the leaves?

A)They separate further.
B)They move closer together.
C)They are unaffected.
D)cannot be determined without further information

Question 12

An atom has more protons than electrons. The atom is

A)a negative ion.
B)a positive ion.
C)an insulator.
D)a conductor.
E)a semiconductor.

Question 13

If two uncharged objects are rubbed together and one of them acquires a positive charge then the other one

A)remains the same.
B)also acquires a positive charge.
C)acquires a negative charge.
D)may or may not acquire a positive charge.
E)may or may not acquire a negative charge.

Question 14

Electric field lines can cross only if both positive and negative charges are involved.

Question 15

State the law of conservation of electric charge.

Question 16

State three properties of conductors in static equilibrium.

Question 17

When atom A loses an electron to atom B,

A)atom A becomes more negative than atom B.
B)atom A acquires more neutrons than atom B.
C)atom A acquires less neutrons than atom B.
D)atom A becomes a positive ion and atom B becomes a negative ion.
E)atom A becomes a negative ion and atom B becomes a positive ion.

Question 18

Compare insulators and conductors on the atomic level.

Question 19

The number of protons in the nucleus of an electrically neutral atom is equal to

A)the number of neutrons in the nucleus.
B)the number of neutrons surrounding the nucleus.
C)the number of electrons surrounding the nucleus.
D)the number of electrons in the nucleus.
E)None of the other choices is correct.

Question 20

Materials in which the electrons are bound very tightly to the nuclei are referred to as

A)insulators.
B)conductors.
C)semiconductors.
D)superconductors.
E)polar.

Question 21

FIGURE 21-6
Four point charges of varying magnitude and sign are arranged on the corners of the square of side d as shown in Fig. 21-6. Which of the arrows shown represents the net force acting on the point charge with a charge +Q?

A)A
B)B
C)C
D)D
E)none of the above

Question 22

When five equal positive charges are uniformly spaced along the x-axis, the force on the next to last charge on the right is directed

A)to the right.
B)possibly in the negative y-direction.
C)zero.
D)possibly in the positive y-direction.
E)to the left.

Question 23

FIGURE 21-8
Three equal point charges are placed at the corners of a square of side d as shown in Fig. 21-8. Which of the arrows shown represents the direction of the net electric field at the center of the square?

A)A
B)B
C)C
D)D
E)none of the above

Question 24

Is it possible to have a zero electric field value between a negative and positive charge along the line joining the two charges?

A)Yes, if the two charges are equal in magnitude.
B)Yes, regardless of the magnitude of the two charges.
C)No, a zero electric field cannot exist between the two charges.
D)cannot be determined without knowing the separation between the two charges
E)cannot be determined without knowing the magnitude of the charges

Question 25

Two charged objects are separated by a distance d. The first charge is larger in magnitude than the second charge.

A)The first charge exerts a larger force on the second charge.
B)The second charge exerts a larger force on the first charge.
C)The charges exert forces on each other equal in magnitude and opposite in direction.
D)The charges exert forces on each other equal in magnitude and pointing in the same direction.

Question 26

FIGURE 21-7
Two charges Q₁ and Q₂ of equal magnitudes and opposite signs are positioned as shown in Fig. 21-7. Which of the shown arrows represents correctly the electric field at point P?

A)A
B)B
C)C
D)D
E)The field is equal to zero at point P.

Question 27

A long line of charge with charge per unit length λ1 is located on the x-axis and another long line of charge with charge per unit length λ2 is located on the y-axis with their centers crossing at the origin. In what direction is the electric field at point z = a on the positive z-axis if λ1 and λ2 are positive?

A)the positive z-direction
B)halfway between the x-direction and the y-direction
C)the negative z-direction
D)all directions are possible parallel to the x-y plane
E)cannot be determined

Question 28

Four equal negative point charges are located at the corners of a square, their positions in the x-y plane being (1, 1), (-1, 1), (-1, -1), (1,-1). The direction of the electric field on the x-axis at (1, 0) is

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

Question 29

FIGURE 21-2
Four point charges of equal magnitudes but with varying signs are arranged on three of the corners and at the center of the square of side d as shown in Fig. 21-2. Which of the arrows shown represents the net force acting on the center charge?

A)A
B)B
C)C
D)D
E)none of the above

Question 30

Two large, flat, horizontally oriented plates are parallel to each other, a distance d apart. Half-way between the two plates the electric field field has a magnitude E. If the separation of the plates is reduced to d/2 what is the magnitude of the electric field half-way between the plates?

A)4E
B)E/2
C)0
D)2E
E)E

Question 31

FIGURE 21-4
Four point charges of equal magnitude and varying signs are arranged on corners of the square of side d as shown in Fig. 21-4. Which of the arrows shown represents the net force acting on the charge at the upper right hand corner of the square?

A)A
B)B
C)C
D)D
E)none of the above

Question 32

Equal charges are located at the vertices of a 3-4-5 triangle. The charge experiencing the largest force is located at

A)the 90° vertex.
B)the 37° vertex.
C)a vertex that depends on the size of the charges.
D)the 53° vertex.
E)cannot be determined.

Question 33

FIGURE 21-9
Three equal point charges are placed at three of the corners of a square of side d as shown in Fig. 21-9. Which of the arrows shown represents the direction of the net electric field at the center of the square?

A)A
B)B
C)C
D)D
E)none of the above

Question 34

FIGURE 21-5
Four point charges of equal magnitude and sign are arranged on the corners of the square of side d as shown in Fig. 21-5. Which of the arrows shown represents the net force acting on the charge at the upper right hand corner of the square?

A)A
B)B
C)C
D)D
E)none of the above

Question 35

In deriving the axial electric field for the ring-shaped charge distribution and the electric field from a long line of charge, the component perpendicular to the resulting field is zero because of what physical property?

A)only net charge is important
B)positive and negative charges cancel
C)superposition
D)integration
E)symmetry

Question 36

Is it possible to have a zero electric field value between two positive charges along the line joining the two charges?

A)Yes, if the two charges are equal in magnitude.
B)Yes, regardless of the magnitude of the two charges.
C)No, a zero electric field cannot exist between the two charges.
D)cannot be determined without knowing the separation between the two charges
E)cannot be determined without knowing the magnitude of the charges

Question 37

FIGURE 21-1
Three equal charges are at three of the corners of a square of side d. A fourth charge of equal magnitude is at the center of the square as shown in Fig. 21-1. Which of the arrows shown represents the net force acting on the charge at the center of the square?

A)A
B)B
C)C
D)D
E)none of the above

Question 38

FIGURE 21-10
Which of the arrows shown in Fig. 21-10 represents the correct direction of the electric field between the two metal plates?

A)A
B)B
C)C
D)D
E)none of the above

Question 39

FIGURE 21-3
Four point charges of equal magnitude but with varying signs are arranged on three of the corners and at the center of the square of side d as shown in Fig. 21-3. Which of the arrows shown represents the net force acting on the center charge?

A)A
B)B
C)C
D)D
E)none of the above

Question 40

The direction of the electric field halfway between an electron and a proton is

A)undefined since the electric field is zero.
B)directed toward the proton.
C)directed toward the electron.
D)perpendicular to the line from the electron to the proton.
E)cannot be determined.

Question 41

Three 3.0 μC charges are at the three corners of an square of side 0.50 m. The last corner is occupied by a -3.0 μC charge. Find the electric field at the center of the square.

Question 42

Q₁ = 6.0 nC is at (0.30 m, 0); Q₂ = -1.0 nC is at (0, 0.10 m); Q₃ = 5.0 nC is at (0, 0). What is the magnitude and direction of the net force on the 5.0 nC charge?

Question 43

FIGURE 21-13
The electric field shown in Fig. 21-13

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

Question 44

In a region where the electric field is uniform, the electric field lines

A)are parallel to one another but the spacing can change from point to point.
B)are parallel to one another and equally spaced.
C)diverge at a constant rate.
D)converge if a negative charge is involved.
E)cannot be determined.

Question 45

A 5.0-μC charge is placed at the 0 cm mark of a meter stick and a -4.0 μC charge is placed at the 50 cm mark. At what point on a line joining the two charges is the electric field zero?

Question 46

A conductor is placed in an electric field under electrostatic conditions. Which of the following statements is correct for this situation?

A)The electric field is zero inside the conductor.
B)All valence electrons go to the surface of the conductor.
C)The electric field on the surface of the conductor is perpendicular to the surface.
D)All of the previous answers apply.
E)None of the answers apply.

Question 47

FIGURE 21-8
Three equal point charges are placed at the corners of a square of side d as shown in Fig. 21-8. What is the correct expression of the net electric field at the center of the square?

Question 48

A ring of negative, uniform charge density is placed on the xz-plane with the center of the ring at the origin. A positive charge moves along the y axis toward the center of the ring. At the moment the charge passes through the center of the ring

A)its velocity and its acceleration reach their maximum values.
B)its velocity is maximum and its acceleration is zero.
C)its velocity and its acceleration have non-zero values but neither is at its maximum.
D)its velocity and its acceleration are both equal to zero.
E)its velocity is zero and its acceleration is maximum.

Question 49

FIGURE 21-11
Fig. 21-11 shows 3 electric charges labeled Q₁, Q₂, Q₃, and some electric field lines in the region surrounding the charges. What are the signs of the 3 charges?

A)Q₁ is positive, Q₂ is negative, Q₃ is positive.
B)Q₁ is negative, Q₂ is positive, Q₃ is negative.
C)Q₁ is positive, Q₂ is positive, Q₃ is negative.
D)All 3 charges are negative.
E)All 3 charges are positive.

Question 50

When static equilibrium is established for a charged conductor, the electric field just inside the surface of the conductor is

A)opposite to the field outside.
B)equal to the perpendicular component of the field outside.
C)equal to the field outside.
D)zero.
E)cannot be determined.

Question 51

Three point charges are placed on the x-axis. A charge of +2.0 μC is placed at the origin, -2.0 μC to the right at x = 50 cm, and +4.0 μC at the 100 cm mark. What are the magnitude and direction of the electrostatic force which acts on the charge at the origin?

Question 52

FIGURE 21-15
Three equal point charges of varying signs are placed on the corners of a square of side d as shown in Fig. 21-15. What is the correct expression for the magnitude of the net electric field at the center of the square?

Question 53

FIGURE 21-14
Fig. 21-14 shows electric field lines near two electric point charges. If Q₁ = -1 μC, what is the value of Q₂?

A)-1 μC
B)0
C)+1 μC
D)+2 μC
E)-2 μC

Question 54

A solid block of metal in electrostatic equilibrium is placed in a uniform electric field. Give a statement 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 points in a direction that is parallel to the exterior field.
D)There is no electric field in the block's interior.
E)Not enough information is given to make a statement concerning the elecric field on the block's interior.

Question 55

FIGURE 21-12
Fig. 21-12 shows two electric charges of equal magnitudes and opposite signs. Electric field lines surrounding the charges are also shown. Which of the shown arrows correctly represents the electric field vector at point P?

A)A
B)B
C)C
D)D
E)The electric field is zero at point P.

Question 56

A 5.0-C charge is 10 m from a small test charge. What is the magnitude and direction of the electric field at the location of the test charge?

Question 57

An electron and a proton, are released simultaneously from rest and start to move towards each other because of the attractive Coulomb force between them. They are initially separated by a distance d. The two particles eventually collide. When they collide,

A)they are closer to the electron's initial position.
B)they are at the midpoint of their initial separation.
C)they are closer to the proton's initial position.
D)Not enough data is given to predict where they collide.

Question 58

Four charges of magnitude +q are placed at the corners of a square whose sides have a length d. What is the magnitude of the total force exerted by the four charges on a charge Q located a distance b along a line perpendicular to the plane of the square and equidistant from the four charges?

Question 59

Can electric field lines intersect in free space?

A)Yes, but only at the midpoint between two equal like charges.
B)Yes, but only at the midpoint between a positive and a negative charge.
C)Yes, but only at the centroid of an equilateral triangle with like charges at each corner.
D)No.

Question 60

Two large, flat, horizontally oriented plates are parallel to each other, a distance d apart. Plate A has a uniform, positive charge density of magnitude σ_A. Plate B has a uniform, negative charge density of magnitude σ_B. What is the magnitude of the electric field half-way between the two plates?

Question 61

A copper penny has a mass of 3.0 g. A total of 4.0 × 10¹² electrons are transferred from one neutral penny to another. If the electrostatic force of attraction between the pennies is equal to the weight of a penny, what is the separation between them?

A)31 cm
B)33 cm
C)35 cm
D)37 cm
E)39 cm

Question 62

A 5.0-C charge is 10 m from a small test charge. What is the magnitude of the force experienced by a 1.0 nC charge placed at the location of the test charge?

A)0.045 N
B)0.45 N
C)4.5 N
D)45 N
E)450 N

Question 63

An atomic nucleus has a charge of +40e. What is the magnitude of the electric field at a distance of 1.0 m from the nucleus?

A)5.4 × 10^-8 N/C
B)5.6 × 10^-8 N/C
C)5.8 × 10^-8 N/C
D)6.0 × 10^-8 N/C
E)6.2 × 10^-8 N/C

Question 64

Three point charges are located at the following positions: Q₁ = 2.00 μC at x = 1.00 m; Q₂ = 3.00 μC at x = 0; Q₃ = -5.00 μC at x = -1.00 m. What is the magnitude of the force on the 3.00-μC charge?

A)5.40 × 10^-2 N
B)0.135 N
C)0.158 N
D)8.10 × 10^-2 N
E)0.189 N

Question 65

FIGURE 21-16
As shown in Fig. 21-16, 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 2.0 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)zero
B)2.0 N
C)2.8 N
D)4.0 N
E)5.3 N

Question 66

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

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

Question 67

A 10 microcoulomb charge is placed at the origin and a 20 microcoulomb charge is placed on the x-axis at x = 40 cm. If an electron is placed on the y-axis at y = 30 cm, what is the magnitude of the force it will experience?

A)0.615 × 10^-12 N
B)2.46 × 10^-13 N
C)4.92 × 10^-13 N
D)1.23 × 10^-13 N
E)2.46 × 10^-14 N

Question 68

Two point charges, initially 2.0 cm apart, experience a 1.0-N force. If they are moved to a new separation of 8.0 cm, what is the electric force between them?

A)1.0 N
B)4.0 N
C)16 N
D)1/4 N
E)1/16 N

Question 69

Three equal charges are located in the x-y plane with coordinates (0, 3m), (4m, 3m), and (4m, 0). The direction of the force on the charge located at (4m, 3m) is the same as the direction of ________

A)4 + 3
.
B)12 + 6
.
C)16 + 9
.
D)9 + 16
.
E)3 + 4
.

Question 70

The electric field along the axis of a ring-shaped charge of total charge Q distributed uniformly is given by E = Qx/(4π ^ε0 (x²+ a²)^3/2) where a is the radius of the ring and x is the distance from the center of the ring. The electric field at the center of the ring is zero and at great distances from the ring approaches zero. At what position is the electric field a maximum for positive values of x?

Question 71

A charge Q = 3 μC is located at the origin. The electric field created by this charge at a point of coordinates (x = 2 m, y = 0m) is equal to ________.

A)( 0.75 × 10³ N/C)
B)( 13.5 × 10³ N/C)
C)( 13.5 × 10⁹ N/C)
D)( 6.75 × 10³ N/C)
E)( 6.75 × 10³ N/C)

Question 72

Two point charges of magnitudes + 5.00 μC, and + 7.00 μC 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)4.58 cm
B)45.8 cm
C)50 cm
D)9.12 cm
E)91.2 cm

Question 73

What are the magnitude and direction of the electric field at a distance of 1.50 m from a 50.0-nC charge?

A)20 N/C away from the charge
B)20 N/C toward the charge
C)10 N/C away from the charge
D)200 N/C away from the charge
E)200 N/C toward the charge

Question 74

Two equal charges of magnitude +1 C are separated by a distance of 1 km. What is the force acting between these two charges?

A)0.9 N
B)9 N
C)90 N
D)900 N
E)9000 N

Question 75

Two point charges of magnitude + 7.00 μC and - 9.00 μC 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)2.99 m
C)- 0.187 m
D)- 2.99 m
E)0.187 m

Question 76

FIGURE 21-17
As shown in Fig. 21-17, a point charge of +Q is placed at the centroid of an equilateral triangle. When a second charge of +Q is placed at one of the triangle's vertices, an electrostatic force of 4.0 N acts on it. What is the magnitude of the force that acts on the center charge due to a third charge of +Q placed at one of the other vertices?

A)zero
B)2.0 N
C)4.0 N
D)8.0 N
E)16 N

Question 77

A charge +3q is placed at x = 0 and a charge +11q is placed at x = 5 units. Where, along the x-axis is the net force on a charge Q equal to zero?

A)x = 1.72 units
B)x = 0.48 units
C)x = 0.27 units
D)x = 0.21 units
E)x = 0.52 units

Question 78

An atomic nucleus has a charge of +40e. An electron is 10^-9 m from the nucleus. What is the force on the electron?

A)2.9 nN
B)1000 C
C)3.7 nN
D)6.8 nN
E)9.2 nN

Question 79

The force of attraction between a - 40.0 μC and + 108 μC charge is 4.00 N. What is the separation between these two charges?

A)2.10 m
B)3.67 m
C)3.12 m
D)2.49 m
E)1.13 m

Question 80

A 1.0-C charge is 15 m from a second charge, and the force between them is 1.0 N. What is the magnitude of the second charge?

A)25 C
B)1.0 C
C)10 nC
D)0.025 C
E)25 nC