Capacitors and Electric Potential Quiz

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.

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.