# Capacitor

The capacitor is a passive component like the inductor and the resistor. The capacitor is a two terminals component and can store energy. Capacitor have multiples uses like signal filtering, noise suppression, coupling/decoupling and voltage spike suppression during big current transient. The capacitance of a capacitor vary and capacitor are build to have a specific capacitance. The unit of capacitance is the farad (F). A farad is define as 1 C/V (coulomb per volt). The capacitance gives you the amount of energy (charge) a capacitor can store. The higher the capacitance is, the more charge it can store.

Capacitors are generally in the range of pF to mF. Bigger capacitors exists but are used for specific applications (1 farad or more). A simple example : the capacitor used in cars for subwoofer amplifier. The capacitor is connected close to the amplifier to supply power during high current spike. This is done so the voltage of the car battery doesn’t drop too much. While not necessary, this helps avoid the lights of your car from dimming during current spike.

The capacitor has two symbols:

The symbol on the left has no polarity. The symbol on the right with the curved line is a polarized capacitor. A polarized capacitor is generally an electrolytic capacitor. A polarized capacitor can only be place in one direction. If it is placed in the wrong direction, it could potentially explode, smoke, spark or stop working. When working with polarized components, always be careful since you could potentially hurt yourself. There is also a third symbol for variable capacitor. It is the symbol on the left with an arrow at 45 degrees going through the two lines. Variable capacitor are use mostly for radio tuning applications.

##### Capacitors in Series

The total capacitance of capacitors placed in series is calculated like parallel resistors :

$\cfrac{1}{Ctot}=\cfrac{1}{C1}+\cfrac{1}{C2}+\cfrac{1}{C3}$

This means that we could replace all 3 capacitors with one capacitor of capacitance Ctot and it would be an equivalent circuit.

The generic formula for capacitors in series would be :

$\cfrac{1}{Ctot}=\cfrac{1}{C1}+\cfrac{1}{Cn}$

##### Capacitors in Parallel

The total capacitance of capacitors placed in parallel is the sum of all capacitances.

In the image above, the total capacitance would be :

$Ctot=C1+C2+C3+C4$

This means that we could replace all four capacitors with one capacitor of capacitance Ctot and it would be an equivalent circuit.

The generic formula for capacitors in parallel would be :

$Ctot=C1+Cn+\dots$