Question 1

Which of the following best describes the direction of the electric field produced by an infinite plane of positive charge?

Accepted Answer

Perpendicular to the plane and away from the charge

Question 2

Given a point charge $$q$$ located at the origin, what is the magnitude of the electric field at a distance $$r$$ from the charge?

Accepted Answer

$$E = \frac{q}{4\pi\$$epsilon_0$$ r^2$}$$

Question 3

A thin, uniformly charged rod of length $$L$$ and total charge $$Q$$ lies along the $$x-$$axis. What is the linear charge density $$\lambda$$?

Accepted Answer

$$\lambda = \frac{Q}{L}$$

Question 4

Which symmetry allows you to conclude that the electric field outside a uniformly charged spherical shell is radial and depends only on the distance from the center?

Accepted Answer

Spherical symmetry

Question 5

What is the electric field at a distance $$r$$ from an infinite line of charge with linear charge density $$\lambda$$?

Accepted Answer

$$E = \frac{\lambda}{2\pi\$$epsilon_0$$ r}$$

Question 6

A parallel-plate capacitor is modeled as two infinite planes of charge. If the surface charge density on each plate is $$\eta$$, what is the electric field between the plates?

Accepted Answer

$$E = \frac{\eta}{\$$epsilon_0$$}$$

Question 7

Which of the following is a consequence of the symmetry principle in electrostatics?

Accepted Answer

The electric field must have the same symmetries as the charge distribution.

Question 8

A charged ring of radius $$R$$ carries a total charge $$Q. $$What is the electric field at a point on the axis of the ring a distance $$z$$ from its center?

Accepted Answer

$$E = \frac{1}{4\pi\$$epsilon_0$$} \frac{Qz}{(z^2$ + R^2$)^{3/2}$$}$

Question 9

Which of the following statements about the electric field inside a uniformly charged spherical shell is correct?

Accepted Answer

The electric field is zero everywhere inside the shell.

Question 10

A dipole consists of charges $$+q$$ and $$-q$$ separated by a distance $$d. $$What is the dipole moment $$\vec{p}$$?

Accepted Answer

$$\vec{p} = qd$$

Question 11

Which of the following best describes the electric field far from a dipole?

Accepted Answer

It falls off as $$1/r^3$$

Question 12

A charged particle of charge $$q is $$placed in a uniform electric field $$\vec{E}. $$What is the force on the particle?

Accepted Answer

$$\vec{F} = q\vec{E}$$

Question 13

Which of the following is NOT a type of symmetry relevant for determining electric fields?

Accepted Answer

Thermal symmetry

Question 14

A uniformly charged disk of radius $$R$$ has a surface charge density $$\sigma. $$What is the total charge $$Q on $$the disk?

Accepted Answer

$$Q = \sigma \pi R^2$

Question 15

Which of the following is true about the electric field produced by an infinite plane of charge with surface charge density $$\eta$$?

Accepted Answer

The field is constant and given by $$E = \frac{\eta}{2\$$epsilon_0$$}$$

Question 16

A coaxial cable consists of two concentric cylindrical conductors. What type of symmetry is most useful for analyzing the electric field in this system?

Accepted Answer

Cylindrical symmetry

Question 17

Which of the following integrals correctly expresses the total charge $$Q$$ distributed along a rod of length $$L$$ with linear charge density $$\lambda$$?

Accepted Answer

$$Q = \$$int_0$$^L \lambda dx$$

Electric Fields: Models, Symmetry, and Charge Distributions

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