Capacitors and Electric Potential Quiz

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Questions and Answers

What happens to the charge on a parallel-plate capacitor if the potential difference doubles?

The charge on each plate decreases by half.

The charge on each plate is tripled.

The charge on each plate doubles. (correct)

The charge on each plate remains the same.

How can you increase the maximum potential difference of a parallel-plate capacitor for a fixed area of the plates and plate separation?

Decree the distance between the plates.

Use a dielectric between the capacitor plates. (correct)

Increase the size of the plates.

Remove the dielectric material completely.

Why is the Earth considered a 'ground' in electric terms?

It can only supply charges to a circuit.

It has a fixed number of charges.

It acts as a capacitor in electrical circuits.

It is capable of accepting or supplying an unlimited number of charges. (correct)

If the potential difference across a capacitor is doubled, by what factor is the electrical potential energy stored in the capacitor multiplied?

4 times as great. Signup and view all the answers

What design factors are important for creating a small capacitor with high capacitance?

The plates should be close together and have a dielectric between them. Signup and view all the answers

What happens to the charge distribution in a dielectric when an electric field is applied?

Negative charge accumulates near the positive plate. Signup and view all the answers

What effect does a dielectric have on the electric field strength in a capacitor?

It reduces the electric field strength. Signup and view all the answers

How does the presence of a dielectric influence capacitance in a parallel-plate capacitor?

Capacitance increases. Signup and view all the answers

Which factor is more significant in a material with a high dielectric constant compared to one with low permittivity?

Higher polarization in response to electric field. Signup and view all the answers

Why is a capacitor preferred over a battery in a camera's flash system?

Capacitors can deliver stored charge faster. Signup and view all the answers

What occurs in a keyboard when a key is pressed?

The capacitance increases as spacing decreases. Signup and view all the answers

What role do dielectrics play in storing energy?

They increase the energy storage capacity. Signup and view all the answers

What is the relationship between the dielectric constant and the energy stored in a dielectric material?

Higher dielectric constant allows for more energy storage. Signup and view all the answers

What is the primary function of a capacitor?

To store electrical potential energy Signup and view all the answers

Which equation represents the relationship between capacitance, electric charge, and potential difference?

$C = q / ΔV$ Signup and view all the answers

How can capacitance be increased in a parallel-plate capacitor?

By increasing the area of the plates Signup and view all the answers

What role does a dielectric play in a capacitor?

It increases capacitance by storing charge Signup and view all the answers

What is the SI unit for capacitance?

Farad Signup and view all the answers

In the context of a sphere capacitor, how does capacitance change with the size of the sphere?

It increases as the radius increases Signup and view all the answers

What material characteristics do dielectrics have?

They resist the flow of electric current Signup and view all the answers

What happens when the potential difference between capacitor plates equals that of a connected battery?

Charge transfer stops Signup and view all the answers

Signup and view all the answers

Study Notes

Capacitance

A capacitor is a device used to store electrical potential energy.
Uses include tuning radio frequencies, sparking in car ignition systems.

Parallel-Plate Capacitor

A simple capacitor design consists of two parallel metal plates separated by a small distance.
This type of capacitor is called a parallel-plate capacitor.
The other type is a sphere capacitor.

Capacitor Charging

The capacitor is energized (charged) by connecting the plates to the two terminals of a battery.
Charge transfer between the plates stops when the potential difference between the plates is equal to the potential difference between the terminals of the battery.

Capacitance Definition

The ability of a conductor to store energy in the form of electrically separated charges is called capacitance.

Capacitance Units

Capacitance (C) is measured in Farads (F).
Electric charge (q) is measured in Coulombs (C).
Potential difference (ΔV) is measured in Volts (V).
The SI unit for capacitance is 1 Farad (F).

Capacitance of a Parallel-Plate Capacitor

The capacitance of a parallel-plate capacitor in a vacuum is calculated as: C = ε₀A/d where:
ε₀ is the permittivity of a vacuum (8.85 x 10⁻¹²).
A is the area of one of the plates.
d is the distance between the plates.

Permittivity

Permittivity reflects the ability of a medium to store a charge in an electric field.

Capacitance of a Sphere Capacitor

The capacitance of a sphere capacitor is calculated as: C = 4πε₀R where:
ε₀ is the permittivity of a vacuum.
R is the radius of the sphere.

Increasing Capacitance

To increase capacitance for a parallel-plate capacitor:
Increase the area of the plates.
Decrease the distance between the plates.
Use a dielectric between the plates.

Dielectric

A dielectric (e.g., air, rubber, glass, waxed paper) inserted between the plates of a capacitor increases the capacitance.
Molecules in the dielectric align with the applied electric field, causing excess negative charge near the positive plate and excess positive charge near the negative plate.
A dielectric reduces the electric field strength.

Capacitors in Flash Attachments

A battery charges the capacitor.
When the shutter is released, the stored charge is released quickly to the flash tube.

Capacitors in Keyboards

Each key is connected to a movable plate.
This changes the capacitance, which triggers the circuit.

Electrical Potential Energy Stored in a Charged Capacitor

PE electric = ½ (q)(ΔV)

Maximum Operating Potential

In practice, there's a limit to the maximum energy (or charge) stored due to electrical breakdown between the capacitor plates when the potential difference is large enough.

Question 1: Charge on a Parallel-Plate Capacitor

If the potential difference doubles, the charge on each plate doubles.

Question 2: Increasing Maximum Potential Difference

Use a dielectric between the capacitor plates.

Question 3: 'Ground' in Electrical Terms

The Earth is considered a "ground" because it can accept or supply an unlimited number of charges.
Any object with this ability can act as a ground.

Question 4: Doubling Potential Difference Impact

If the potential difference doubles, the electrical potential energy will be quadrupled.

Question 5: Designing a Small Capacitor with High Capacitance

The plates should be close together and the dielectric should have high permittivity.

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Description

Test your knowledge on the principles of parallel-plate capacitors, including the effects of potential difference and design considerations for high capacitance. This quiz covers fundamental concepts essential for understanding electric circuits and energy storage in capacitors.