Capacitor: definition, types, unit, formula, symbol

Generally, a capacitor is a Charge-storing element. It consumes the electrical energy and stores charge inside the Dielectric, up to the equilibrium attained with the applied voltage. As it stores electrical energy, it can be a source. When the source is absent and it connects to other passive elements. Which are like Resistor, Inductor, Capacitor. But, If the potential difference lasts inside the device. It provides energy as a source. As in the charging and discharging of a Battery. Also, I am discussing the capacitor definition, types, unit, formula, and symbol.F

What is a capacitor definition?

The terminal voltage is proportional to the integral of the current with respect to time. Alter, the current in a capacitor is equal to capacitance C times the rate of change of voltage. Hence, this is known as the definition of the capacitor.


Capacitor as Passive element

Since, the active elements should be able to provide power or power gain to the circuit for an infinite duration of time. That is why the charged inductor and capacitor are not ACTIVE elements. Hence, these are PASSIVE elements.

What is Capacitance?

By definition, Capacitance is the ratio of Charge and voltage across the element. The unit of the capacitor capacitance is Farad, the symbol is “F”.


Types of the capacitors

  1. Parallel plates.
  2. Mica capacitor.
  3. Electrolytic.
  4. Paper capacitor.
  5. Film capacitor.
  6. Non-polarized .
  7. Ceramic.

To illustrate we will discuss only a few capacitors of important types.

1. Parallel plates capacitor

The name itself explains that there are two parallel plates. Generally, parallel plates contain Dielectric material between them. These dielectric stores charge. When there is a potential difference between them. Hence, the charge storing capability depends on the dielectric inside.

C=\frac{\epsilon * A}{d} 
  • C= charge in coulomb.
  • A= Area of the plates.
  • d= distance between the plates.
  • epsilon for air is 1.
\epsilon \rightarrow depends~on~the~dielectric~placed~inside!

Therefore, the Capacitance of the air as a dielectric is lesser. Than any other dielectric material inside. Because capacitance is directly proportional to the dielectric constant.

2. Mica capacitor

Mica capacitor is of two types. One uses natural minerals and the other uses silver mica as a dielectric.

“Clamped capacitor” uses natural minerals as a dielectric. Whereas “Silver mica capacitor” uses silver mica as a dielectric.

Clamped mica capacitors are obsolete due to their unwanted characteristics. The mica sheets are sandwiched together. Edges are coated with the metal to form silver mica capacitors. And then, this assembly dipped in the epoxy to protect the environment.

Mica capacitor meets the requirements for Stability, Reliability, and Small size.

Mica capacitors are low electrical loss capacitors. Used at higher frequencies and this is stable chemically, mechanically, and electrically. Due to its crystalline structure binding, it is having typical layer to layer structure.

The most commonly used types of mica are phlogopite and muscovite mica. Muscovite mica has better electrical properties. Whereas phlogopite mica has better temperature resistance property.

3. Electrolytic capacitor

Generally, if there is a requirement of large capacitance, the Electrolytic capacitor has that capability.

A thin metal layer is in use, for the one terminal, and on the other terminal, has a gelatinous substance (jelly or semi-liquid). The dielectric plate is a thin layer of oxide, it forms electro-chemically in production with the thickness of the film and it is less than the ten microns.

Electrolytic capacitors are having thin insulating layer around them. And it is also possible to make a capacitor of large capacitance. Which is having a very small distance between the terminals.

Capacitors must have a polarity check for the applied voltage. Otherwise, it will be not working as of need, if it is having some charge previously. If the polarity is not as of need, then its insulating oxide layer will break and the device will damage permanently.

The use of the Electrolytic capacitor is mainly in the DC power supply, to reduce harmonics in voltage waveform. Because these are having large Capacitance and small size. Also used for coupling and decoupling.

The disadvantage is their relatively low voltage rating. Because of the polarization of electrolytic capacitors.

4. Paper capacitor

The paper or oil paper or thin wax paper separates two tin foil sheets. These paper sheets act as a dielectric. These sandwiched foils roll in cylindrical form. A plastic capsule encloses it. The two terminals of the capacitors connect to the two tin plates separately.

In the early ages, it uses paper as a dielectric. As of now, the capacitors are using the materials like plastic sheets. That’s why it is called a “paper capacitor“.

The range of the paper capacitor varies from 0.001 to 2 micro farad. And voltage rating is very high like 2000V.


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