Capacitors - Understanding Basics and Applications

Capacitors

• Capacitors are devices designed to store electric charge.
• They are used in various applications like radio reception, filtering, and heart defibrillators.
• Capacitors typically have two conducting parts separated by an insulator.
• Connecting the capacitor terminals to a battery causes a charge to build up on the plates.

Learning Objectives

• Understand capacitance, charge, and potential difference in capacitors.
• Learn the role of dielectrics in modifying capacitance and reducing electric field.
• Calculate equivalent capacities and charges on individual capacitors, along with potential differences.

Capacitor

• A capacitor stores electrical charge.
• Applications include radio reception, filtration, and heart defibrillators.
• Consists of two conducting parts separated by an insulator.
• When connected to a battery, a charge builds up.

Parallel Plate Capacitors

• Two parallel conducting plates separated by a distance constitute a parallel plate capacitor .
• The charge and voltage are related via an electric field.
• More electric field lines correspond to greater charge.
• The magnitude of the electric field is directly related to the voltage and inversely proportional to the separation between the plates (d)

Charge Stored

• Amount of charge a capacitor can hold depends on the applied voltage and the capacitor's size and physical characteristics.

Capacitance

• Ability of a capacitor to store charges.
• Represented as C = Q / V, where Q is the charge and V is the voltage.
• Unit of capacitance is the farad (F), named after Michael Faraday.
• Capacitance depends on factors like the area of plates, the distance between the plates, and the insulating material in between.

Factors Affecting Capacitance

• Plate Area (A): Larger area leads to higher capacitance.
• Plate Separation (d): Smaller separation leads to higher capacitance.
• Dielectric Material: The permittivity constant (€) influences capacitance; higher values result in higher capacitance.

Parallel Plate Capacitor Formula

• C = ε₀ A / d, where ε₀ is the permittivity of free space, A is the area of one plate, and d is the distance between them.

Permittivity of Materials

• Different materials have different permittivity values.
• The permittivity of some common dielectric materials are listed in a table (this table is provided in the image).

Example Problem

• An example of a problem demonstrates how to calculate capacitance given plate area, separation, and dielectric type.
• Another example problem demonstrates how to determine capacitance and potential given values for electric field, charge, and the separation between parallel plates.

Combination of Capacitors

• Parallel Combination:
  • Total capacitance equals the sum of individual capacitances.
  • Increases the effective plate area.
  • The total capacitance of parallel capacitors is found/calculated similarly to the total resistance of series resistors.
• Series Combination:
  • 1/Total Capacitance = 1/Capacitor 1 + 1/Capacitor 2 + 1/Capacitor 3
  • Similar to inverting and adding resistances of resistors connected in series, which are in a series circuit are added
  • The charges on the individual plates are the same.

Role of Dielectrics

• Dielectrics are insulating materials like glass, plastic, or ceramic.
• They do not conduct electricity easily.
• They increase capacitance when inserted between the capacitor plates.
• Polarization: The electric field from the plates causes the dielectric molecules to slightly separate positive and negative charges.
• Reduced Field Strength: This internally generated field opposes the external field, reducing the overall field strength between the plates.

This quiz explores the fundamental concepts of capacitors, including their structure, function, and applications in real-life scenarios like radio reception and medical devices. You'll learn about capacitance, dielectrics, and how to calculate equivalent capacities. Test your knowledge on how capacitors store electric charge and their role in electrical circuits.