Question 1

Which of the following best describes the physical meaning of electric flux through a closed surface?

Accepted Answer

It is the total charge enclosed by the surface, divided by the electric constant.

Question 2

A long, straight wire carries a uniform positive linear charge density $$\lambda. $$Using Gauss’s law, what is the magnitude of the electric field at a distance $$r$$ from the wire?

Accepted Answer

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

Question 3

A thin, infinite sheet of charge has a uniform surface charge density $$\sigma. $$What is the electric field just outside the sheet?

Accepted Answer

$$E = \dfrac{\sigma}{2\$$epsilon_0$$}$$

Question 4

Which of the following is a necessary condition for using Gauss’s law to easily calculate the electric field?

Accepted Answer

The Gaussian surface must match the symmetry of the electric field.

Question 5

A solid conductor contains a hollow cavity with no charge inside. What is the net electric flux through a Gaussian surface inside the cavity?

Accepted Answer

It is zero.

Question 6

A point charge $$q is $$placed at the center of a spherical cavity inside a neutral conductor. What is the charge induced on the inner surface of the cavity?

Accepted Answer

$$-q$$

Question 7

Which of the following statements about conductors in electrostatic equilibrium is correct?

Accepted Answer

All excess charge resides on the surface of the conductor.

Question 8

A Faraday cage is used to shield sensitive equipment from external electric fields. Why does this work?

Accepted Answer

The cage redistributes charges on its surface so that the field inside is zero.

Question 9

A positive test charge moves in the direction of a uniform electric field. What happens to its electric potential energy?

Accepted Answer

It decreases.

Question 10

If a negative charge moves opposite to the direction of a uniform electric field, what is the sign of the work done by the field and what happens to the potential energy?

Accepted Answer

Positive work, potential energy decreases.

Question 11

The electric potential energy of two point charges $$q$$ and $$q_0$$ separated by a distance $$r is $$given by which formula?

Accepted Answer

$$U = \dfrac{q q_0$}{4\pi\$$epsilon_0$$ r}$$

Question 12

For two charges of the same sign, what is the sign of their electric potential energy and how does it change as the distance between them increases?

Accepted Answer

Positive; decreases toward zero as distance increases.

Question 13

Which of the following best describes the electric potential at a point in space?

Accepted Answer

It is the potential energy per unit charge at that point.

Question 14

A point charge of $$-3.00\ \mu	ext{C} is $$located at the center of a spherical cavity of radius $$6.60\ 	ext{cm}$$ inside an insulating solid sphere with charge density $$7.35 	imes 10$$^{-4}$$\ 	ext{C/m}^3. $$What is the total charge enclosed by a Gaussian surface at $$r = 9.20\ 	ext{cm}$$ from the center?

Accepted Answer

$$Q_{enc} = -3.00\ \mu	ext{C} + \dfrac{4}{3}\pi (0.0920^3$ - 0.0660^3$) 	imes 7.35 	imes 10$$^{-4}$$\ 	ext{C}$$

Question 15

Which of the following is true about the electric field inside a conductor in electrostatic equilibrium?

Accepted Answer

It is always zero.

Question 16

A battery has a potential difference of $$1.5\ 	ext{V}$$ between its terminals. What is the change in electric potential energy when a $$2.0\ \mu	ext{C}$$ charge moves from the negative to the positive terminal?

Accepted Answer

$$3.0 	imes 10$$^{-6}$$\ 	ext{J}$$

Question 17

Which of the following is a correct application of Gauss’s law?

Accepted Answer

Calculating the electric field outside a uniformly charged sphere.

Question 18

A water hose is used as an analogy for electric flux. Which of the following best matches the analogy?

Accepted Answer

The total water passing through a surface is analogous to electric flux.

Question 19

A collection of point charges $$q_1$$, $$q_2$$, $$q_3$$, ...$$ are located at distances r_1$, r_2$, r_3$, ...$$ from a test charge $$q_0. $$What is the total electric potential energy of the system?

Accepted Answer

$$U = \dfrac{q_0$}{4\pi\$$epsilon_0$$} \sum_i \dfrac{q_i}{r_i}$$

Gauss's Law and Electric Potential: Study Notes for Physics College Students

Study Guide - Practice Questions

Study Guide - Flashcards