Deck 24: Electric Fields

Question 1

A uniformly charged rod (length = 2.0 m, charge per unit length = 5.0 nC/m) is bent to form one quadrant of a circle. What is the magnitude of the electric field at the center of the circle?

A)62 N/C
B)56 N/C
C)50 N/C
D)44 N/C
E)25 N/C

Answer 1

50 N/C

Question 2

A +15-nC point charge is placed on the x axis at x = 1.5 m, and a −20-nC charge is placed on the y axis at y = −2.0m. What is the magnitude of the electric field at the origin?

A)105 N/C
B)15 N/C
C)75 N/C
D)45 N/C
E)60 N/C

Answer 2

75 N/C

Question 3

A 16-nC charge is distributed uniformly along the x axis from x = 0 to x = 4 m. Which of the following integrals is correct for the magnitude (in N/C) of the electric field at x = +10 m on the x axis?

A)
B)
C)
D)
E)none of these

Answer 3

Question 4

A charge of 80 nC is uniformly distributed along the x axis from x = 0 to x = 2.0 m. Determine the magnitude of the electric field at a point on the x axis with x = 8.0 m.

A)30 N/C
B)15 N/C
C)48 N/C
D)90 N/C
E)60 N/C

Question 5

A 12-nC charge is distributed uniformly along the y axis from y = 0 to y = 4 m. Which of the following integrals is correct for the x component of the electric field at x = 2 m on the x axis?

A)
B)
C)
D)
E)none of these

Question 6

If Q = 80 nC, a = 3.0 m, and b = 4.0 m in the figure, what is the magnitude of the electric field at point P?

A)45 N/C
B)70 N/C
C)29 N/C
D)47 N/C
E)92 N/C

Question 7

A uniform linear charge of 2.0 nC/m is distributed along the x axis from x = 0 to x = 3 m. Which of the following integrals is correct for the y component of the electric field at y = 4 m on the y axis?

A)
B)
C)
D)
E)none of these

Question 8

A charge (uniform linear density = 9.0 nC/m) is distributed along the x axis from x = 0 to x = 3.0 m. Determine the magnitude of the electric field at a point on the x axis with x = 4.0 m.

A)81 N/C
B)74 N/C
C)61 N/C
D)88 N/C
E)20 N/C

Question 9

If a = 60 cm, b = 80 cm, Q = −6.0 nC, and q = 6.0 nC, what is the magnitude of the electric field at point P in the figure?

A)65 N/C
B)55 N/C
C)60 N/C
D)52 N/C
E)67 N/C

Question 10

A +2.0-nC point charge is placed at one corner of a square (1.5 m on a side), and a −3.0-nC charge is placed on a corner diagonally away from the first charge. What is the magnitude of the electric field at either of the two unoccupied corners?

A)20 N/C
B)14 N/C
C)4.0 N/C
D)12 N/C
E)8.0 N/C

Question 11

A +20-nC point charge is placed on the x axis at x = 2.0 m, and a −25-nC point charge is placed on the y axis at y = −3.0 m. What is the direction of the electric field at the origin?

A)209°
B)61°
C)29°
D)241°
E)151°

Question 12

A uniformly charged rod (length = 2.0 m, charge per unit length = 3.0 nC/m) is bent to form a semicircle. What is the magnitude of the electric field at the center of the circle?

A)64 N/C
B)133 N/C
C)48 N/C
D)85 N/C
E)34 N/C

Question 13

If a = 60 cm, b = 80 cm, Q = −6.0 nC, and q = 4.0 nC, what is the magnitude of the electric field at point P?

A)35 N/C
B)42 N/C
C)52 N/C
D)64 N/C
E)104 N/C

Question 14

If a = 60 cm, b = 80 cm, Q = −6.0 nC, and q = 3.0 nC in the figure, what is the magnitude of the electric field at point P?

A)71 N/C
B)56 N/C
C)60 N/C
D)53 N/C
E)67 N/C

Question 15

A charge Q is placed on the x axis at x = +4.0 m. A second charge q is located at the origin. If Q = +75 nC and q = −8.0 nC, what is the magnitude of the electric field on the y axis at y = +3.0 m?

A)19 N/C
B)23 N/C
C)32 N/C
D)35 N/C
E)21 N/C

Question 16

If Q = 16 nC, a = 3.0 m, and b = 4.0 m, what is the magnitude of the electric field at point P?

A)33 N/C
B)31 N/C
C)24 N/C
D)19 N/C
E)13 N/C

Question 17

A 40-μC charge is positioned on the x axis at x = 4.0 cm. Where should a −60-μC charge be placed to produce a net electric field of zero at the origin?

A)−5.3 cm
B)5.7 cm
C)4.9 cm
D)−6.0 cm
E)+6.0 cm

Question 18

Charge of uniform density 4.0 nC/m is distributed along the x axis from x = −2.0 m to x = +3.0 m. What is the magnitude of the electric field at the point x = +5.0 m on the x axis?

A)16 N/C
B)13 N/C
C)19 N/C
D)26 N/C
E)5.0 N/C

Question 19

If a = 60 cm, b = 80 cm, Q = −4.0 nC, and q = 1.5 nC, what is the magnitude of the electric field at point P?

A)68 N/C
B)72 N/C
C)77 N/C
D)82 N/C
E)120 N/C

Question 20

A charge of 25 nC is uniformly distributed along a circular arc (radius = 2.0 m) that is subtended by a 90-degree angle. What is the magnitude of the electric field at the center of the circle along which the arc lies?

A)81 N/C
B)61 N/C
C)71 N/C
D)51 N/C
E)25 N/C

Question 21

When gravitational, magnetic and any forces other than static electric forces are not present, electric field lines in the space surrounding a charge distribution show

A)the directions of the forces that exist in space at all times.
B)only the directions in which static charges would accelerate when at points on those lines
C)only the directions in which moving charges would accelerate when at points on those lines.
D)tangents to the directions in which either static or moving charges would accelerate when passing through points on those lines.
E)the paths static or moving charges would take.

Question 22

A rod (length = 2.0 m) is uniformly charged and has a total charge of 40 nC. What is the magnitude of the electric field at a point which lies along the axis of the rod and is 3.0 m from the center of the rod?

A)40 N/C
B)45 N/C
C)24 N/C
D)90 N/C
E)36 N/C

Question 23

The velocity of a particle (m = 10 mg, q = −4.0 μC) at t = 0 is 20 m/s in the positive x direction. If the particle moves in a uniform electric field of 20 N/C in the positive x direction, what is the particle's speed at t = 5.0 s?

A)60 m/s
B)20 m/s
C)45 m/s
D)40 m/s
E)70 m/s

Question 24

Charge Q is uniformly distributed over a line segment of length 2L, as shown below. When the x-coordinate of point P is x, the magnitude of the y-component of the electric field at point P is

A)0.
B) .
C) .
D) .
E) .

Question 25

A 24-nC charge is distributed uniformly along the x axis from x = 2 m to x = 6 m. Which of the following integrals is correct for the magnitude (in N/C) of the electric field at x = +8 m on the x axis?

A)
B)
C)
D)
E)none of these

Question 26

A uniform linear charge of 2.0 nC/m is distributed along the x axis from x = 0 to x = 3 m. What is the x component of the electric field at y = 2 m on the y axis?

A)−5.0 N/C
B)−4.0 N/C
C)−5.7 N/C
D)−6.2 N/C
E)−9.0 N/C

Question 27

A particle (q = 3.0 mC, m = 20 g) has a speed of 20 m/s when it enters a region where the electric field has a constant magnitude of 80 N/C and a direction which is the same as the velocity of the particle. What is the speed of the particle 3.0 s after it enters this region?

A)68 m/s
B)44 m/s
C)56 m/s
D)80 m/s
E)36 m/s

Question 28

A uniform linear charge density of 7.0 nC/m is distributed along the y axis from y = 2 m to y = 5 m. Which of the following integrals is correct for the magnitude (in N/C) of the electric field at y = 0 on the y axis?

A)
B)
C)
D)
E)none of these

Question 29

A uniform linear charge of 3.0 nC/m is distributed along the y axis from y = −3 m to y = 2m. Which of the following integrals is correct for the magnitude of the electric field at y = 4 m on the y axis?

A)
B)
C)
D)
E)none of these

Question 30

A particle (m = 20 mg, q = −5.0 μC) moves in a uniform electric field of 60 N/C in the positive x direction. At t = 0, the particle is moving 30 m/s in the positive x direction and is passing through the origin. Determine the maximum distance beyond x = 0 the particle travels in the positive x direction.

A)25 m
B)20 m
C)15 m
D)30 m
E)60 m

Question 31

A particle (mass = 5.0 g, charge = 40 mC) moves in a region of space where the electric field is uniform and is given by Ex = −2.3 N/C, Ey = Ez = 0. If the position and velocity of the particle at t = 0 are given by x = y = z = 0 and vz = 20 m/s, vx = vy = 0, what is the distance from the origin to the particle at t = 2.0 s?

A)60 m
B)54 m
C)69 m
D)78 m
E)3.2 m

Question 32

A charge of 50 nC is uniformly distributed along the y axis from y = 3.0 m to y = 5.0 m. What is the magnitude of the electric field at the origin?

A)18 N/C
B)50 N/C
C)30 N/C
D)15 N/C
E)90 N/C

Question 33

A uniform linear charge of 2.0 nC/m is distributed along the x axis from x = 0 to x = 3 m. Which of the following integrals is correct for the x component of the electric field at y = 2 m on the y axis?

A)
B)
C)
D)
E)none of these

Question 34

A particle (q = 4.0 mC, m = 50 g) has a velocity of 25 m/s in the positive x direction when it first enters a region where the electric field is uniform (60 N/C in the positive y direction). What is the speed of the particle 5.0 s after it enters this region?

A)49 m/s
B)35 m/s
C)32 m/s
D)44 m/s
E)24 m/s

Question 35

A particle (m = 20 mg, q = −5.0 μC) moves in a uniform electric field of 60 N/C in the positive x direction. At t = 0, the particle is moving 25 m/s in the positive x direction and is passing through the origin. How far is the particle from the origin at t = 2.0 s?

A)80 m
B)20 m
C)58 m
D)10 m
E)30 m

Question 36

A particle (mass = 5.0 g, charge = 40 mC) moves in a region of space where the electric field is uniform and is given by Ex = 2.5 N/C, Ey = Ez = 0. If the velocity of the particle at t = 0 is given by vy = 50 m/s, vx = vz = 0, what is the speed of the particle at t = 2.0 s?

A)81 m/s
B)72 m/s
C)64 m/s
D)89 m/s
E)25 m/s

Question 37

Which one of the diagrams below is not a possible electric field configuration for a region of space which does not contain any charges?

A)
B)
C)
D)
E)

Question 38

When a positive charge q is placed in the field created by two other charges Q1 and Q2, each a distance r away from q, the acceleration of q is

A)in the direction of the charge Q1 or Q2 of smaller magnitude.
B)in the direction of the charge Q1 or Q2 of greater magnitude.
C)in the direction of the negative charge if Q1 and Q2 are of opposite sign.
D)in the direction of the positive charge if Q1 and Q2 are of opposite sign.
E)in a direction determined by the vector sum of the electric fields of Q1 and Q2.

Question 39

A particle (mass = 5.0 g, charge = 40 mC) moves in a region of space where the electric field is uniform and is given by Ex = −5.5 N/C, Ey = Ez = 0. If the position and velocity of the particle at t = 0 are given by x = y = z = 0 and vx = 50 m/s, vy = vz = 0, what is the distance from the origin to the particle at t = 2.0 s?

A)60 m
B)28 m
C)44 m
D)12 m
E)88 m

Question 40

A particle (mass = 4.0 g, charge = 80 mC) moves in a region of space where the electric field is uniform and is given by Ex = −2.5 N/C, Ey = Ez = 0. If the velocity of the particle at t = 0 is given by vx = 80 m/s, vy = vz = 0, what is the speed of the particle at t = 2.0 s?

A)40 m/s
B)20 m/s
C)60 m/s
D)80 m/s
E)180 m/s

Question 41

A negatively charged particle is moving in the +x-direction when it enters a region with a uniform electric field pointing in the +x-direction. Which graph gives its position as a function of time correctly? (Its initial position is x = 0 at t = 0.)

A)
B)
C)
D)
E)

Question 42

A positively charged particle is moving in the +y-direction when it enters a region with a uniform electric field pointing in the +x-direction. Which of the diagrams below shows its path while it is in the region where the electric field exists. The region with the field is the region between the plates bounding each figure. The field lines always point to the right. The x-direction is to the right; the y-direction is up.

A)
B)
C)
D)
E)

Question 43

In a diagram of charges and electric field lines charge has twelve field lines going outward from it and charge has three field lines going into it. If one of the charges is 100 nC, what is the other one?

A)25 nC
B)100 nC
C)-25 nC
D)-100 nC
E)Both answers b and c can be correct.

Question 44

Two uniform rods, each of length 2.0 m, are bent to form semicircles. One rod has a charger per unit lent of 1.5 nC/m, and the other has a charge per unit length of -1.5 nC/m. The semicircles are joined to make a circle. What is the magnitude of the electric field at the center of the circle?

A)42 N/C
B)84 N/C
C)34 N/C
D)68 N/C
E)0

Question 45

Two imaginary spherical surfaces of radius R and 2R respectively surround a positive point charge Q located at the center of the concentric spheres. When compared to the number of field lines N1 going through the sphere of radius R, the number of electric field lines N2 going through the sphere of radius 2R is

A) .
B) .
C)N2 = N1.
D)N2 = 2N1.
E)N2 = 4N1.

Question 46

Suppose a uniform electric field of 4 N/C is in the positive x direction. When a charge is placed at and fixed to the origin, the resulting electric field on the x axis at x = 2 m becomes zero. What is the magnitude of the electric field at x = 4 m on the x axis at this time?

A)0
B)1 N/C
C)2 N/C
D)4 N/C
E)More information is needed to find the resulting field magnitude at this position.

Question 47

The electron gun in a television tube accelerates electrons (mass = 9.11 × 10⁻³¹ kg, charge = 1.60 × 10⁻¹⁹ C) from rest to 3.00 × 10⁷ m/s within a distance of 2.00 cm. What electric field is required?

Question 48

A proton moving at 3 × 10⁴ m/s is projected at an angle of 30° above a horizontal plane. If an electric field of 400 N/C is directed downwards, how long does it take the proton to return to the horizontal plane? (HINT: Ignore gravity.) [mProton = 1.67 × 10⁻²⁷ kg, qProton = +1.6 × 10⁻¹⁹ C.]