Understanding Capacitor Principles and Capacitance Formulas

Capacitors

Definition

A capacitor is a device whose function is to store electrical charges for later use.

Types of Capacitors

Capacitors are divided into two groups: fixed and variable.

• Fixed capacitors: These include paper, ceramic, and electrolytic types. In paper capacitors, the plates are made of high-purity aluminum sheets and the dielectric is high-quality paper. In ceramic capacitors, the plates are silver and ceramic is used as the dielectric. In electrolytic capacitors, one plate is aluminum and the other is an electrolyte, using aluminum oxide as the dielectric.
• Variable capacitors: These are capacitors that can vary their capacity through mechanical means, using air or plastic as the dielectric.

Dielectric

Materials that do not conduct electricity are called dielectrics.

Capacitance

Definition

Capacitance is the magnitude measured by the ratio between the charge on either of the two conductors and the potential difference between them.

Formula

C = q / V

• C: The capacitance of the capacitor.
• V: The potential difference between the plates.
• q: The charge on each of the plates.

Note: It is important to note that the charge q is the magnitude of the charge on one of the plates, as the net charge of the capacitor is zero.

Units of Capacity

If the equation C = q / V is expressed with q in Coulombs and V in Volts, the capacity is expressed in Coulomb/Volt. This relationship is called a Farad (F), which is the unit of capacity in the International System of Units (SI).

The Farad

A Farad is the capacitance acquired when a charge of one Coulomb is applied with a potential difference of one Volt.

Equivalents

Parallel Plate Capacitors

Characteristics

A plane parallel plate capacitor is a device that has the following features:

• It consists of a pair of parallel plates of finite area.
• The separation between the plates is negligible compared to its dimensions.

Energy of a Charged Capacitor

Equations

In the process of charging a capacitor, the potential difference between the plates is not constant; it passes from an initial value (Vi = 0) to a final value (V). The average potential difference in the charging process is given by: