310102l Capacitance and Capacitive Reactance 2025 (TF)

Capacitance and Capacitive Reactance

Overview

• Focuses on capacitance and its applications in instrumentation technology.

• Key objectives include:

  • Understanding capacitance and capacitor construction

  • Comprehending dielectric strength

  • Analyzing AC capacitive circuits

  • Exploring power relationships in capacitive circuits

  • Identifying types and applications of capacitors

Capacitance

• Definition: The ability of an electrical device to store energy in an electrostatic field.

• Capacitor Function: Ability to store and release electrical charge.

• Opposition to Voltage Change: Capacitance opposes changes in voltage, symbolized as C.

• Measurement: Capacitance is measured in farads (F), usually noted in smaller units:

  • Microfarads (µF) = 10^-6 F

  • Picofarads (pF) = 10^-12 F

Capacitor Construction

• Basic Components: Consists of two conductive plates separated by a dielectric material.

• Factors Affecting Capacitance:

  • Type of Dielectric (E_r): Different materials affect capacitance.

  • Area of Plates (A): Larger plate area increases capacitance.

  • Distance Between Plates (d): Closer plates lead to greater capacitance.

• Capacitance Formula:[ C = \frac{(8.85 \times 10^{-12}) \cdot E_r \cdot A}{d} ]

Dielectric Strength

• Definition: Measurement of a material's ability to insulate against electric flow.

• Typical Dielectric Strengths:

  • Air: 3 kV/mm

  • Paper: 20 kV/mm

  • Mica: 200 kV/mm

  • Porcelain: 8 kV/mm

Charging and Discharging Capacitors

• Charging Process: Capacitors store energy when connected to a voltage source, characterized by charging curves.

• Discharging Process: Energy releases through a resistor, showing a decline in voltage over time.

• Key Concepts:

  • A coulomb (C) represents electric charge, defined as the quantity of electricity transported in one second by a constant current of one ampere.

AC Capacitive Circuits

• Current-Voltage Relationship: In AC circuits, current leads voltage by 90°.

• Capacitive Reactance Formula:[ X_C = \frac{1}{2 \pi f C} ]

  • Where ( X_C ) = capacitive reactance, ( f ) = frequency, ( C ) = capacitance.

Capacitor Types

• Common Types of Capacitors:

  • Oil-filled Capacitor: Used in high-voltage applications.

  • Mica Capacitor: Suitable for high frequency and stability.

  • Ceramic Capacitor: Used in various electronic applications for stability and low capacitance.

  • Electrolytic Capacitor: Known for high capacitance values, often with specific polarity.

Practical Applications

• Understanding the characteristics of various capacitors and their appropriate applications is crucial for efficient electronic circuit design.