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AP Physics C: Electricity and Magnetism Practice Quiz: Dielectrics

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

Test your understanding with short quizzes. This quiz has 10 questions to check your progress.

Question 1 of 10

How do electric charges within a dielectric material typically respond when placed in an external electric field?

All Questions (10)

How do electric charges within a dielectric material typically respond when placed in an external electric field?

A) They move freely from one end of the material to the other.

B) They are completely unaffected by the external electric field.

C) The material becomes polarized as the charges shift slightly.

D) They are ejected from the material, creating a current.

Correct Answer: C

The provided text states that in a dielectric material, 'the material becomes polarized in the presence of an external electric field' because the charges are not as free to move as in a conductor.

When a dielectric is placed between the plates of an isolated parallel-plate capacitor, what is the effect on the electric field between the plates?

A) The electric field increases.

B) The electric field decreases.

C) The electric field remains unchanged.

D) The electric field reverses direction.

Correct Answer: B

The content explicitly states: 'The electric field between the plates of an isolated parallel-plate capacitor decreases when a dielectric is placed between the plates.'

The dielectric constant, κ, is defined as the ratio of the electric permittivity of a material (ε) to the permittivity of free space (ε₀). Which equation correctly represents this relationship?

A) κ = ε × ε₀

B) κ = ε₀ / ε

C) κ = ε / ε₀

D) κ = ε - ε₀

Correct Answer: C

The content provides the relevant equation directly: κ = ε / ε₀.

The electric field in an isolated, air-filled capacitor is E₀. After a dielectric material is inserted, the new electric field is E. How is the dielectric constant, κ, of the material determined from these two values?

A) κ = E / E₀

B) κ = E₀ / E

C) κ = E₀ × E

D) κ = E₀ - E

Correct Answer: B

The provided text gives the derived equation relating the dielectric constant to the initial and final electric fields: κ = E₀ / E.

An isolated parallel-plate capacitor has an electric field of 200 V/m. A dielectric slab with a dielectric constant κ = 4 is inserted, completely filling the space between the plates. What is the magnitude of the new electric field?

A) 800 V/m

B) 200 V/m

C) 100 V/m

D) 50 V/m

Correct Answer: D

Using the equation κ = E₀ / E, we can solve for the new field E. E = E₀ / κ = (200 V/m) / 4 = 50 V/m.

What key characteristic distinguishes a dielectric material from a conductor in terms of electric charge behavior?

A) Charges in a dielectric are positively charged, while in a conductor they are negatively charged.

B) Charges in a dielectric are not as free to move throughout the material as they are in a conductor.

C) Dielectrics cannot be polarized, whereas conductors can.

D) Dielectrics increase the external electric field, while conductors decrease it.

Correct Answer: B

The content states, 'In a dielectric material, electric charges are not as free to move as they are in a conductor.'

According to the provided text, what is the overall consequence of inserting a dielectric into a capacitor?

A) It has no effect on the capacitor.

B) It changes the properties of the capacitor.

C) It causes the capacitor to discharge immediately.

D) It converts the capacitor into a resistor.

Correct Answer: B

The first point in the content is to 'Describe how a dielectric inserted between the plates of a capacitor changes the properties of the capacitor,' which directly implies that its properties are changed.

The electric field inside an isolated capacitor drops from 60 N/C to 20 N/C when a dielectric is inserted. What is the dielectric constant (κ) of the material?

A) 1/3

B) 3

C) 40

D) 1200

Correct Answer: B

The dielectric constant is the ratio of the original electric field to the final electric field: κ = E₀ / E = (60 N/C) / (20 N/C) = 3.

A certain material has an electric permittivity (ε) that is five times the permittivity of free space (ε₀). What is the dielectric constant (κ) of this material?

A) 0.2

B) 1

C) 5

D) 25

Correct Answer: C

Given ε = 5ε₀ and the formula κ = ε / ε₀, we can substitute to find κ = (5ε₀) / ε₀ = 5.

The reduction of the electric field inside a capacitor by a dielectric is a direct consequence of which phenomenon?

A) The conduction of free charges across the dielectric.

B) The increase in charge on the capacitor plates.

C) The polarization of the dielectric material.

D) The decrease in the permittivity of the space.

Correct Answer: C

The text explains that a dielectric 'becomes polarized in the presence of an external electric field.' This polarization creates an internal field that opposes the external field from the capacitor plates, leading to a decrease in the net electric field.