Question 1

A negatively charged particle is placed between the plates of a parallel plate capacitor and moves from point A to point B. Which of the following statements is correct about the direction of the electric field and the force on the particle?

Accepted Answer

The electric field points from the positive plate to the negative plate, and the force on the negative charge is opposite to the field.

Question 2

A permanent electric dipole is placed at rest in a uniform electric field. What happens to the dipole?

Accepted Answer

The center of the dipole does not move, but the dipole rotates to align with the field.

Question 3

A permanent electric dipole is placed at rest in a non-uniform electric field created by a positive point charge. What is the net motion of the dipole's center?

Accepted Answer

The center of the dipole moves toward the region of stronger electric field (toward the point charge).

Question 4

The torque $$	au on an $$electric dipole with dipole moment $$\vec{p} in a $$uniform electric field $$\vec{E} is $$given by which of the following expressions?

Accepted Answer

$$	au = pE \sin 	heta$$

Question 5

Two identical electric dipoles are placed in identical uniform electric fields, but in one case the field points to the right and in the other to the left. The angle between $$\vec{p}$$ and $$\vec{E} is$$ $$	heta in $$both cases. How do the magnitudes of the torques compare?

Accepted Answer

The torques are equal in magnitude in both cases.

Question 6

Which of the following best explains why water molecules heat up in a microwave oven?

Accepted Answer

The oscillating electric field exerts a torque on the permanent dipole moments of water molecules, causing them to rotate and transfer energy to thermal motion.

Question 7

Which of the following electric field patterns is consistent with the symmetry of an infinitely long, uniformly charged cylinder aligned with the $$x-$$axis?

Accepted Answer

A field that points radially outward from the axis at every point.

Question 8

An infinite plane sheet of charge lies in the $$xz-$$plane at $$y=0. $$Which of the following electric field patterns is consistent with the symmetry of the charge distribution?

Accepted Answer

A field that points perpendicular to the plane (along $$y$$), with the same magnitude everywhere.

Question 9

A spherical shell and a cubical shell are both centered at the origin and have charge uniformly distributed on their surfaces. Which of the following statements is true about the symmetry of the electric field outside each shell?

Accepted Answer

The electric field outside the sphere is spherically symmetric, but the field outside the cube has only the symmetries of the cube.

Question 10

Three charged spheres are arranged along a line. Gaussian surfaces A, B, and C enclose different combinations of these spheres. If A encloses zero net charge, B encloses $$+q$$, and C encloses $$-q$$, how should the electric fluxes $$\Phi_A$$, $$\Phi_B$$, and $$\Phi_C be $$ranked from smallest to largest?

Accepted Answer

$$\Phi_C \u003c \Phi_A \u003c \Phi_B$$

Question 11

A uniform electric field $$\vec{E}$$ points in the $$x-$$direction with magnitude $$3000\,\mathrm{N/C}. A $$surface of area $$1.0\,\mathrm{m}^2 is $$tilted $$30^\circ$$ from the $$xy-$$plane. What is the electric flux through the surface?

Accepted Answer

$$1500\,\mathrm{N\cdot m^2$/C}$$

Question 12

Which of the following is the correct mathematical statement of Gauss's Law?

Accepted Answer

$$\Phi_E = \oint \vec{E} \cdot d\vec{A} = \dfrac{Q_{	ext{encl}}}{\$$varepsilon_0$$}$$

Question 13

A metal bucket with a metal lid has zero excess charge. A metal ball with charge $$+q is $$placed inside the bucket, not touching the bucket. At electrostatic equilibrium, what is the charge on the inner and outer surfaces of the bucket?

Accepted Answer

Inner surface: $$-q$$, Outer surface: $$+q$$

Question 14

An infinitely long cylindrical rod of radius $$r_0$$ has uniform charge density $$\rho. $$What is the relationship between the magnitude of the electric field $$E$$ and the distance $$r$$ from the axis for $$r \u003e r_0$?

Accepted Answer

$$E \propto 1/r$$

Question 15

An infinitely long cylindrical rod of radius $$r_0$$ has uniform charge density $$\rho. $$What is the relationship between the magnitude of the electric field $$E$$ and the distance $$r$$ from the axis for $$r \u003c r_0$?

Accepted Answer

$$E \propto r$$

Question 16

A cubical shell centered on the origin has charge uniformly distributed on its surface. Which of the following Gaussian surfaces allows you to calculate the electric field at a point $$P on $$the shell using Gauss's law?

Accepted Answer

This field cannot be calculated using either surface.

Question 17

A closed surface encloses a region of space with no net charge. What is the net electric flux through the surface?

Accepted Answer

Zero

Question 18

An infinitely long cylindrical rod of radius $$r_0$$ has uniform charge density $$\rho. $$Consider two coaxial cylindrical Gaussian surfaces: one of length $$2l$$ and radius $$r_0$$, and one of length $$l$$ and radius $$r_0/2$. What is the ratio of the electric flux through the first surface to the second?

Accepted Answer

2

Question 19

A Gaussian surface encloses two point charges, $$+q$$ and $$-q. $$What is the net electric flux through the surface?

Accepted Answer

Zero

Electric Fields, Dipoles, and Gauss's Law: Structured Study Notes ch 24

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