What is a capacitor

A capacitor (available from a few cents to tens of euros) is an electrical component that builds up, stores and discharges charge. The charge build-up occurs between plates or conductors that are separated from each other; This is also reflected in the symbol for a capacitor:

  • ||-

The amount of charge (Q), or the capacitance (C), of a capacitor, is expressed in farads (F).


A capacitor that has a charge of 1 coulomb, where the voltage between the plates is 1 volt, has a capacitance of 1 farad.

The relationship in formula form is:

Q = C x U

Where the charge Q in coulombs on the capacitor is the result of the multiplication between the voltage U in volts across the capacitor and the capacitance C in farads.

Types of capacitors and their application

There are different types of capacitors intended for different applications. In addition, capacitors are made of different materials. There are different types of capacitors, some of them are:

  • ceramic capacitors; small capacitance and high voltage, also called circa (ceramic capacitor)
  • mica; small capacity and high voltage
  • electrolytic capacitor; high capacitance, low ohmic resistance, often used as voltage stabilization, also called el cap (electrolytic capacitor)
  • variable; are used when fine-tuning is required, often in transmission technology, also called trimmers (such as variable resistors)

The capacitor in an electrical circuit

Like other electronic components, the capacitor also has certain properties in an electronic circuit. Without going into too much detail about the infinitely many applications of the capacitor, whether or not in combination with other types of components, only the basic circuits will be discussed here.

Parallel connection

If capacitors are included in parallel in a circuit, the sum of the individual capacitances may be regarded as replacement capacitance. In a parallel arrangement, the voltage across the capacitors is equal, however, the charge will be distributed across them.

C replacement = C1 + C2 + Cn

Series connection

In a series circuit of capacitors, the current flowing in the individual capacitors is the same. The voltage across the entire series circuit is the sum of the individual voltages across the capacitor.

Itotal = I1 = I2 = In


The replacement capacitance of capacitors in a series circuit, as is the case for resistors in series, is the inverse of the sum of the inverses of the individual capacitances.

1/Creplacement = (1/C1 + 1/C2 + 1/Cn)

Capacity indication

There are capacitors where the capacitance including the unit can be found on the housing, eg 100 F. If there is no unit after the value, then pF (picofarad) can generally be assumed.

There are also capacitors that use color coding for electronic components. The first band indicates the tens, the second band the units, and the third band the factor by which the multiplication takes place. The results of the 3 bands mentioned are in the unit pF. The fourth band represents the tolerance and the fifth band the maximum allowable tension.

In addition, there are capacitors where the capacitance is determined by an imprint of 3 digits; for example, an imprint of 103 has an actual capacitance of 10 x 103 = 10,000 pF = 10 nF

Finally, the capacity can also be measured using so-called capacity meters.

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