Deck 22: Electric Fields

Question 1

An isolated charged point particle produces an electric field with magnitude E at a point 2 m away. At a point 1 m from the particle the magnitude of the field is:

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

Answer 1

4E

Question 2

The units of the electric field are:

A) J/(C.m)
B) J/C
C) J.C
D) J/m
E) none of these

Answer 2

J/(C.m)

Question 3

The equation E = kq/r² applies to:

A) only pointlike particles
B) any symmetric objects
C) all objects
D) any spherical object
E) it applies to all objects as long as they are not moving

Answer 3

only pointlike particles

Question 4

The diagrams below depict four different charge distributions. The charged particles are all the same distance from the origin. The electric field at the origin:

A) is least for situation 1
B) is greatest for situation 3
C) is zero for situation 4
D) is downward for situation 1
E) is downward for situation 3

Question 5

Two thin spherical shells, one with radius R and the other with radius 2R, surround an isolated charge point particle. The ratio of the number of field lines through the larger sphere to the number through the smaller is:

A) 1
B) 2
C) 4
D) 1/2
E) 1/4

Question 6

Two protons (p₁ and p₂) are on the x axis, as shown below. The directions of the electric field at points 1, 2, and 3 respectively, are:

A) $\rightarrow$ , $\leftarrow$ , $\rightarrow$
B) $\leftarrow$ , $\rightarrow$ , $\leftarrow$
C) $\leftarrow$ , $\rightarrow$ , $\rightarrow$
D) $\leftarrow$ , $\leftarrow$ , $\leftarrow$
E) $\leftarrow$ , $\leftarrow$ , $\rightarrow$

Question 7

Choose the correct statement concerning electric field lines:

A) field lines may cross
B) field lines are close together where the field is large
C) field lines point away from negatively charged particle
D) a point charge particle released from rest moves along a field line
E) none of these are correct

Question 8

A certain physics textbook shows a region of space in which two electric field lines cross each other. We conclude that:

A) at least two point charges are present
B) an electrical conductor is present
C) an insulator is present
D) the field points in two directions at the same place
E) the author made a mistake

Question 9

The diagram shows the electric field lines in a region of space containing two small charged spheres (Y and Z). Then:

A) Y is negative and Z is positive
B) the magnitude of the electric filed is the same everywhere
C) the electric field is strongest midway between Y and Z
D) Y is positive and Z is negative
E) Y and Z must have the same sign

Question 10

Two point particles, with charges of q₁ and q₂, are placed a distance r apart. The electric field is zero at a point P between the particles on the line segment connecting them. We conclude that:

A) q₁ and q₂ must have the same magnitude and sign
B) P must be midway between the particles
C) q₁ and q₂ must have the same sign but may have different magnitudes
D) q₁ and q₂ must have equal magnitudes and opposite signs
E) q₁ and q₂ must have opposite signs and may have different magnitudes

Question 11

The units of the electric field are:

A) N.C²
B) C/N
C) N
D) N/C
E) C/m²

Question 12

The diagram shows the electric field lines due to two charged parallel metal plates. We conclude that:

A) the upper plate is positive and the lower plate is negative
B) a proton at X would experience the same force if it were placed at Y
C) a proton at X experiences a greater force than if it were placed at Z
D) a proton at X experiences less force than if it were placed at Z
E) an electron at X could have its weight balanced by the electrical force

Question 13

An electric field is most directly related to:

A) the momentum of a test charge
B) the kinetic energy of a test charge
C) the potential energy of a test charge
D) the force acting on a test charge
E) the charge carried by a test charge

Question 14

As used in the definition of electric field, a "test charge":

A) has zero charge
B) must be a proton
C) has charge of magnitude 1.6 *10^-19 C
D) must be an electron
E) none of the above

Question 15

Electric field lines:

A) are trajectories of a test charge
B) are vectors in the direction of the electric field
C) form closed loops
D) cross each other in the region between two point charges
E) are none of the above

Question 16

Experimenter A uses a test charge q₀ and experimenter B uses a test charge 2q₀ to measure an electric field produced by stationary charges. A finds a field that is:

A) the same as the field found by B
B) greater than the field found by B
C) less than the field found by B
D) either greater or less than the field found by B, depending on the masses of the test charges
E) either greater or less than the field found by B, depending on the accelerations of the test charges

Question 17

An isolated point charged point particle produces an electric field with magnitude E at a point 2 m away from the charge. A point at which the field magnitude is E/4 is:

A) 0.5 m away from the charge
B) 1 m away from the charge
C) 2 m away from the charge
D) 4 m away from the charge
E) 8 m away from the charge

Question 18

Let k denote 1/4 $\pi$$\varepsilon$ ₀. The magnitude of the electric field at a distance r from an isolated point charge q is:

A) kq/r
B) kr/q
C) kq/r³
D) kq/r²
E) kq²/r²

Question 19

The electric field at a distance of 10 cm from an isolated point particle with a charge of 2 *10^-9 C is:

A) 1.8 N/C
B) 18 N/C
C) 180 N/C
D) 1800 N/C
E) none of these

Question 20

The diagram shows a particle with positive charge Q and a particle with negative charge-Q. The electric field at point P on the perpendicular bisector of the line joining them is:

A) $\uparrow$
B) $\downarrow$
C) $\rightarrow$
D) $\leftarrow$
E) zero

Question 21

An electric dipole consists of two charges, ±2.5 µC, separated by 1.0 x 10^-4 m and centered on the origin. If the dipole is oriented along the x axis, what is the electric field at x = 15 cm?

A) 0 N/C
B) 100 N/C
C) 200 N/C
D) 670 N/C
E) 1300 N/C

Question 22

Positive charge +Q is uniformly distributed on the upper half of a semicircular rod and negative charge -Q is uniformly distributed on the lower half. What is the direction of the electric field at point P, the center of the semicircle?

A) $\uparrow$
B) $\downarrow$
C) $\leftarrow$
D) $\rightarrow$
E)

Question 23

Positive charge Q is uniformly distributed on a semicircular rod. What is the direction of the electric field at point P, the center of the semicircle?

A) $\uparrow$
B) $\downarrow$
C) $\leftarrow$
D) $\rightarrow$
E)

Question 24

A spherical shell has an inner radius of 3.7 cm and an outer radius of 4.5 cm. If charge is distributed uniformly throughout the shell with a volume density of 6.1* 10^-4 C/m³ the total charge is:

A) 1.0 * 10^-7 C
B) 1.3 * 10^-7 C
C) 2.0 *10^-7 C
D) 1.7 *10^-6 C
E) 5.0 * 10^-6 C

Question 25

The diagram shows two identical particles, each with positive charge Q. The electric field at point P on the perpendicular bisector of the line joining them is:

A) $\uparrow$
B) $\downarrow$
C) $\rightarrow$
D) $\leftarrow$
E) zero

Question 26

A total charge of 6.3 * 10^-8 C is distributed uniformly throughout a 2.7-cm radius sphere. The volume charge density is:

A) 3.7 *10^-7 C/m³
B) 6.9* 10^-6 C/m³
C) 6.9 *10^-6 C/m²
D) 2.5*10^-4 C/m³
E) 7.6*10^-4 C/m³

Question 27

Charge is placed on the surface of a 2.7-cm radius isolated conducting sphere. The surface charge density is uniform and has the value 6.9* 10^-6 C/m². The total charge on the sphere is:

A) 5.7 * 10^-10 C
B) 1.6 * 10^-8 C
C) 3.2 *10^-8 C
D) 6.3 * 10^-8 C
E) 7.5 * 10^-4 C

Question 28

Comparing the field of a single point charge with the field of an electric dipole,

A) the field of the point charge decreases more rapidly with distance
B) the field of the point charge decreases less rapidly with distance
C) the field of the point charge decreases more rapidly with distance but only along the dipole axis
D) the field of the point charge decreases less rapidly with distance but only perpendicular to the dipole axis
E) the fields decrease equally rapidly with distance

Question 29

Two point particles, one with charge +8 *10^-9 C and the other with charge-2 * 10^-9 C, are separated by 4 m. The electric field midway between them is:

A) 9 * 10⁹ N/C
B) 13,500 N/C
C) 135,000 N/C
D) 36 *10^-9 N/C
E) 22.5 N/C

Question 30

Two point particles, with the same charge, are located at two vertices of an equilateral triangle. A third charged particle is placed so the electric field at the third vertex is zero. The third particle must:

A) be on the perpendicular bisector of the line joining the first two charges
B) be on the line joining the first two charges
C) be identical to the first two charges
D) have the same magnitude as the first two charges but may have a different sign
E) be at the center of the triangle

Question 31

Two charged point particles are located at two vertices of an equilateral triangle and the electric field is zero at the third vertex. We conclude:

A) the two particles have charges with opposite signs and the same magnitude
B) the two particles have charges with opposite signs and different magnitudes
C) the two particles have identical charges
D) the two particles have charges with the same sign but different magnitudes
E) at least one other charged particle is present

Question 32

An electric dipole consists of a particle with a charge of +6 * 10^-6 C at the origin and a particle with a charge of -6 * 10^-6 C on the x axis at x = 3 * 10^-3 m. Its dipole moment is:

A) 1.8 * 10^-8 C.m, in the positive x direction
B) 1.8 *10^-8 C.m, in the negative x direction
C) 0 C.m, because the net charge is 0
D) 1.8 *10^-8 C.m, in the positive y direction
E) 1.8 * 10^-8 C.m, in the negative y direction

Question 33

A charged particle is placed in an electric field that varies with location. No force is exerted on this charge:

A) at locations where the electric field is zero
B) at locations where the electric field strength is 1/(1.6 F*10^-19) N/C
C) if the particle is moving along a field line
D) if the particle is moving perpendicular to a field line
E) if the field is caused by an equal amount of positive and negative charge

Question 34

A disk with a uniform positive surface charge density lies in the x-y plane, centered on the origin. Along the positive z axis, the direction of the electric field is:

A) in the +z direction
B) in the -z direction
C) in the +x direction
D) in the +y direction
E) there is no field along the positive z axis

Question 35

Two point charges are arranged as shown. In which region could a third charge +1 C be placed so that the net electrostatic force on it is zero?

A) I only
B) I and II only
C) III only
D) I and III only
E) II only

Question 36

The electric field due to a uniform distribution of charge on a spherical shell is zero:

A) everywhere
B) nowhere
C) only at the center of the shell
D) only inside the shell
E) only outside the shell

Question 37

Positive charge +Q is uniformly distributed on the upper half of a rod and a negative charge -Q is uniformly distributed on the lower half. What is the direction of the electric field at point P, on the perpendicular bisector of the rod?

A) $\uparrow$
B) $\downarrow$
C) $\rightarrow$
D) $\leftarrow$
E)

Question 38

A disk with a uniform positive surface charge density lies in the x-y plane, centered on the origin. The disk contains 2.5 x 10^-6 C/m² of charge, and is 7.5 cm in radius. What is the electric field at z = 15 cm?

A) 30 N/C
B) 300 N/C
C) 3000 N/C
D) 3.0 x 10⁴ N/C
E) 3.0 x 10⁷ N/C

Question 39

An electric dipole consists of a particle with a charge of +6 *10^-6 C at the origin and a particle with a charge of -6 *10^-6 C on the x axis at x = 3 *10^-3 m. The direction of the electric field due to the dipole at points on the x axis is:

A) in the positive x direction
B) in the negative x direction
C) in the positive y direction
D) in the negative y direction
E) in the positive x direction between the charges and in the negative x direction elsewhere

Question 40

A cylinder has a radius of 2.1 cm and a length of 8.8 cm. Total charge 6.1 * 10^-7 C is distributed uniformly throughout. The volume charge density is:

A) 7.4 * 10^-11 C/m³
B) 5.3 *10^-5 C/m³
C) 5.3 * 10^-5 C/m²
D) 8.5 *10^-4 C/m³
E) 5.0 * 10^-3 C/m³

Question 41

The magnitude of the force of a 400-N/C electric field on a 0.02-C point charge is:

A) 8 N
B) 5* 10^-5 N
C) 8 * 10^-3 N
D) 0.08 N
E) 2 * 10³ N

Question 42

An electric dipole is oriented parallel to a uniform electric field, as shown. It is rotated to one of the five orientations shown below. Rank the final orientations according to the change in the potential energy of the dipole-field system, most negative to most positive.

A) 1, 2, 3, 4
B) 4, 3, 2, 1
C) 1, 2, 4, 3
D) 3, then 2 and 4 tie, then 1
E) 1, then 2 and 4 tie, then 3

Question 43

The force exerted by a uniform electric field on a dipole is:

A) parallel to the dipole moment
B) perpendicular to the dipole moment
C) parallel to the electric field
D) perpendicular to the electric field
E) none of the above

Question 44

When the dipole moment of a dipole in a uniform electric field rotates to become more nearly aligned with the field:

A) the field does positive work and the potential energy increases
B) the field does positive work and the potential energy decreases
C) the field does negative work and the potential energy increases
D) the field does negative work and the potential energy decreases
E) the field does no work

Question 45

A 200-N/C electric field is in the positive x direction. The force on an electron in this field is:

A) 200 N in the positive x direction
B) 200 N in the negative x direction
C) 3.2 * 10^-17 N, in the positive x direction
D) 3.2 * 10^-17 N, in the negative x direction
E) 0 N

Question 46

A charged oil drop with a mass of 2 *10^-4 kg is held suspended by a downward electric field of 300 N/C. The charge on the drop is:

A) +1.5 * 10⁶ C
B) -1.5 * 10⁶ C
C) +6.5 * 10^-6 C
D) -6.5 *10^-6 C
E) 0 C

Question 47

A uniform electric field of 300 N/C makes an angle of 25 $\degree$ with the dipole moment of an electric dipole. If the torque exerted by the field has a magnitude of 2.5 *10^-7 N.m, the dipole moment must be:

A) 8.3 *0 10^-10 C.m
B) 9.2 * 10^-10 C.m
C) 2.0 * 10^-9 C.m
D) 8.3 * 10^-5 C.m
E) 1.8 * 10^-4 C.m

Question 48

The purpose of Milliken's oil drop experiment was to determine:

A) the mass of an electron
B) the charge of an electron
C) the ratio of charge to mass for an electron
D) the sign of the charge on an electron
E) viscosity

Question 49

The dipole moment of a dipole in a 300-N/C electric field is initially perpendicular to the field, but it rotates so it is in the same direction as the field. If the moment has a magnitude of 2 *10^-9 C.m the work done by the field is:

A) -12 * 10^-7 J
B) -6 *10^-7 J
C) 0 J
D) 6 *10^-7 J
E) 12 *10^-7 J

Question 50

An electron traveling north enters a region where the electric field is uniform and points north. The electron:

A) speeds up
B) slows down
C) veers east
D) veers west
E) continues with the same speed in the same direction

Question 51

An electron traveling north enters a region where the electric field is uniform and points west. The electron:

A) speeds up
B) slows down
C) veers east
D) veers west
E) continues with the same speed in the same direction

Question 52

The diagrams show four possible orientations of an electric dipole in a uniform electric field Rank them according to the magnitude of the torque exerted on the dipole by the field, least to greatest.

A) 1, 2, 3, 4
B) 4, 3, 2, 1
C) 1, 2, 4, 3
D) 3, then 2 and 4 tie, then 1
E) 1, then 2 and 4 tie, then 3

Question 53

An electric dipole of dipole moment 4.5 x 10^-9 C·m is in a 250 N/C electric field. If the electric field points east, and the dipole moment vector points 37° west of south, what is the potential energy?

A) -6.8 x 10^-8 J
B) -9.0 x 10^-7 J
C) 0 J
D) 6.8 x 10^-8 J
E) 9.0 x 10^-7 J

Question 54

The torque exerted by an electric field on a dipole is:

A) parallel to the field and perpendicular to the dipole moment
B) parallel to both the field and dipole moment
C) perpendicular to both the field and dipole moment
D) parallel to the dipole moment and perpendicular to the field
E) not related to the directions of the field and dipole moment

Question 55

An electric field exerts a torque on a dipole only if:

A) the field is parallel to the dipole moment
B) the field is not parallel to the dipole moment
C) the field is perpendicular to the dipole moment
D) the field is not perpendicular to the dipole moment
E) the field is uniform