AP Physics C: Electricity and Magnetism Practice Quiz: Electric Fields

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026

Test your understanding with short quizzes. This quiz has 14 questions to check your progress.

Question 1 of 14

The electric field at a point in space is defined as which of the following?

A)The total charge divided by the distance from the charge.B)The electric force per unit charge exerted on a test charge at that point.C)The total electric force on all charges in the vicinity.D)The work done to move a charge from infinity to that point.

All Questions (14)

The electric field at a point in space is defined as which of the following?

A) The total charge divided by the distance from the charge.

B) The electric force per unit charge exerted on a test charge at that point.

C) The total electric force on all charges in the vicinity.

D) The work done to move a charge from infinity to that point.

Correct Answer: B

This is the direct definition of the electric field, as given by the equation $\vec{E}=\frac{\vec{F_{E}}}{q}$. It describes the force that would be felt by a standardized 'test' charge placed at that location.

A solid, uncharged conducting sphere is placed in a uniform external electric field. Which statement is true once the sphere reaches electrostatic equilibrium?

A) The electric field inside the sphere is equal to the external field.

B) The electric field inside the sphere is zero.

C) Excess positive charge accumulates at the center of the sphere.

D) The electric field lines pass through the sphere unchanged.

Correct Answer: B

A key property of a conductor in electrostatic equilibrium is that the net electric field within its volume is zero. The free charges on the conductor rearrange themselves on the surface to cancel out the external field inside.

Two point charges, +Q and -Q, are placed on the x-axis at x = -a and x = +a, respectively. At the origin (x=0), the net electric field...

A) is zero.

B) points in the positive x-direction.

C) points in the negative x-direction.

D) points in the positive y-direction.

Correct Answer: B

The positive charge at x=-a creates an electric field at the origin pointing in the +x direction (away from +Q). The negative charge at x=+a also creates an electric field at the origin pointing in the +x direction (towards -Q). Since both individual fields point in the same direction, their vector sum is non-zero and points in the positive x-direction.

A hollow conducting sphere is given a net negative charge. Once the system reaches electrostatic equilibrium, where will the excess charge be located?

A) Uniformly distributed throughout the volume of the sphere's material.

B) Concentrated at the geometric center of the sphere.

C) Distributed on the outer surface of the sphere.

D) Distributed on the inner surface of the sphere.

Correct Answer: C

For a conductor in electrostatic equilibrium, any excess charge resides entirely on its surface because the like charges repel each other and move as far apart as possible. For a hollow sphere with no charges inside the cavity, the charge will be on the outer surface.

A small test charge of +q is placed at a point P where the electric field has a magnitude E. The electric force on the charge is F. If the test charge is replaced by a new test charge of -2q, what is the new electric force on this charge at point P?

A) F, in the same direction.

B) 2F, in the same direction.

C) F/2, in the opposite direction.

D) 2F, in the opposite direction.

Correct Answer: D

The electric force is given by $\vec{F_E} = q\vec{E}$. The original force is $\vec{F} = (+q)\vec{E}$. The new force is $\vec{F}_{new} = (-2q)\vec{E} = -2(q\vec{E}) = -2\vec{F}$. The magnitude is 2F, and the negative sign indicates the direction is opposite to the original force.

Two positive point charges, +Q and +4Q, are separated by a distance L. At what point on the line connecting the two charges is the net electric field equal to zero?

A) At a distance of L/2 from the +Q charge.

B) At a distance of L/3 from the +Q charge.

C) At a distance of L/4 from the +Q charge.

D) The electric field is never zero between the charges.

Correct Answer: B

For the net field to be zero, the fields from the two charges must be equal in magnitude and opposite in direction. This can only happen at a point between the two positive charges. Let the point be a distance x from +Q. The magnitudes of the fields must be equal: $kQ/x^2 = k(4Q)/(L-x)^2$. This simplifies to $1/x^2 = 4/(L-x)^2$. Taking the square root gives $1/x = 2/(L-x)$, which solves to L-x = 2x, or x = L/3.

Which of the following best describes the electric field created by a single, isolated positive point charge?

A) The field lines point radially inward toward the charge.

B) The field lines point radially outward from the charge.

C) The field lines form concentric circles around the charge.

D) The field is uniform in all directions.

Correct Answer: B

By convention, the electric field lines originate from positive charges and point radially outward, indicating the direction of the force that would be exerted on a positive test charge.

A student measures the electric field at a specific point to be $\vec{E}$. If the student doubles the magnitude of the test charge used for the measurement, what will be the new measured value of the electric field at that same point?

A) $\vec{E}/2$

B) $\vec{E}$

C) $2\vec{E}$

D) $4\vec{E}$

Correct Answer: B

The electric field at a point is a property of the source charges creating the field, not the test charge used to measure it. While the force on the test charge will double ($\vec{F_E} = q\vec{E}$), the ratio $\vec{F_E}/q$ remains constant. Therefore, the electric field $\vec{E}$ is unchanged.

A key difference in the electrostatic behavior of a charged conductor compared to a charged insulator is that...

A) only conductors can hold a net charge.

B) the electric field inside a charged insulator must be zero.

C) excess charge on a conductor resides on its surface, while in an insulator it can be distributed throughout the volume.

D) electric field lines can end on an insulator but not on a conductor.

Correct Answer: C

In a conductor, charges are free to move and will repel each other until they are as far apart as possible, which is on the surface. In an insulator, charges are not free to move, so if charge is placed inside the volume, it will remain there.

An electric force of 10 N is exerted on a charge of +2 C placed at a certain point in space. What is the magnitude of the electric field at that point?

A) 20 N/C

B) 10 N/C

C) 5 N/C

D) 0.2 N/C

Correct Answer: C

Using the definition of the electric field, $E = F_E / q$. Plugging in the values, $E = 10 \text{ N} / 2 \text{ C} = 5 \text{ N/C}$.

At a point P, an electric field $\vec{E}_1$ points due north and an electric field $\vec{E}_2$ of equal magnitude points due east. Both fields are created by nearby charged objects. What is the direction of the net electric field at point P?

A) North

B) East

C) Southwest

D) Northeast

Correct Answer: D

The net electric field is the vector sum of the individual fields. Adding a vector pointing north and a vector of equal magnitude pointing east results in a resultant vector that points exactly northeast (at a 45-degree angle between north and east).

For a conductor in electrostatic equilibrium, which of the following quantities must be zero everywhere inside the material of the conductor?

A) The excess charge density.

B) The electric potential.

C) The electric field.

D) The electric force on the entire conductor.

Correct Answer: C

A fundamental property of a conductor in electrostatic equilibrium is that the net electric field inside the material of the conductor is zero. If it were not, the free charges would move, and it would not be in equilibrium.

Consider a configuration of several fixed point charges. To determine the electric field at a specific empty point in space, one must...

A) calculate the scalar sum of the magnitudes of the fields from each charge.

B) find the electric field from only the closest charge to the point.

C) calculate the vector sum of the electric fields produced individually by each charge.

D) place a test charge at the point and measure the total charge of the configuration.

Correct Answer: C

The principle of superposition states that the net electric field at any point due to a group of charges is the vector sum of the electric fields produced by each charge individually at that point.

A neutral, solid conducting block is placed in a uniform external electric field that points to the right. After electrostatic equilibrium is reached, which statement correctly describes the charge distribution and internal field?

A) The left side of the block is positively charged, the right side is negatively charged, and the internal electric field is zero.

B) The left side of the block is negatively charged, the right side is positively charged, and the internal electric field is zero.

C) The entire block has a net positive charge, and the internal electric field points to the left.

D) The block remains neutral everywhere, and the internal electric field is equal to the external field.

Correct Answer: B

The external field (pointing right) exerts a force on the free electrons in the conductor, pushing them to the left. This leaves a net positive charge (a deficit of electrons) on the right side and a net negative charge (an excess of electrons) on the left side. This induced charge separation creates an internal electric field pointing to the left that exactly cancels the external field, resulting in a net electric field of zero inside the conductor.