Capacitor definition
Capacitor is a device capable of accumulating electrical charges when one potential difference is established between your terminals. THE capacitance of capacitors, in turn, is the measure of how much charge the device is capable of accumulating for a given potential difference.
Capacitors are generally produced in a simple way, formed by two parallel conducting plates, called armatures, which may or may not be filled with a highly medium. dielectric (insulating).
What are capacitors for?
Capacitors can be used for other purposes besides their main function, which is store electrical charges. These devices can be used on circuits powered by alternating electrical currents, when the formation of a continuous electrical current is desired, as in the case of household appliances, such as refrigerators, blenders, machines washing and so on.
An electrical current, however, will not flow through the circuit until the capacitors are fully charged. This can reduce wear produced by the big
variations of electrical current generated when an electronic device is switched on or off.Due to their great ease in storing electrical charges, capacitors can also be used to meet the demand for high electrical currents required by some high-power circuit, such as the large stereos used in shows.
Lookalso: Capacitor Association
Capacitance Formula
Capacitance is a physical quantity related to the amount of electrical charges a capacitor is capable of storing for a given potential difference. The greater its capacitance, the greater the amount of charge stored by the capacitor for the same electrical voltage.
We can calculate capacitance by the ratio between the amount of stored charges and the electrical voltage:
Subtitle:
Ç – capacitance (F – farad)
Q – stored electrical charge (C-coulomb)
U – electrical voltage or potential difference (V – volts)
The capacitance unit in the International System of Units (SI) is the farad (F), unit that equals coulomb per volt (C/V).
Capacitance is also affected by geometric factors of the capacitors: the distance (d) between the armature plates of the capacitors and their area (THE) influence the maximum amount of charges that can be accumulated by them. Another factor that can affect the capacitance and the permissivenessdielectric (ε) from the middle inserted between the plates of a capacitor: the greater the dielectric permittivity of the medium, the greater will be the maximum amount of charge stored in a capacitor.
Thus, the capacitance of a parallel plate capacitor can be calculated using the following relationship:
Subtitle:
Ç – capacitance (F)
ε – electrical permittivity of the medium (F/m)
THE – area of the capacitor plates (m²)
d – distance between capacitor plates (m)
The figure below shows a schematic of a parallel plate capacitor:
In the figure above, A is the area of one of the plates, and d is the distance between them.
Formula of energy stored in capacitors
We can calculate the amount of electrical potential energy stored between the armatures of a capacitor using the following equation:
Subtitle:
ANDPOT – electrical potential energy (J – joules)
Q – electric charge (C – coulombs)
U – Electrical voltage (or potential difference) (V – volts)
Through the above equation and the capacitance formula, we can also deduce a second equation, given by:
Subtitle:
ANDPOT – electrical potential energy (J)
Ç – capacitance (F)
U – Electrical voltage or potential difference (V)
Exercise solved
A parallel-plate capacitor of capacitance equal to 2.0 µF is connected to a potential of 220.0 V. Calculate the magnitude of the electrical charge stored between the capacitor's armatures and its electrical potential energy.
Resolution:
To solve this exercise, initially, we will use the capacitance formula that relates charge and electrical voltage. Watch:
According to the data provided by the exercise statement, we have to:
Then, to calculate the electrical potential energy stored in the capacitor, we use the following formula:
In this way, we will have the following resolution:
By Rafael Hellerbrock
Graduated in Physics
Source: Brazil School - https://brasilescola.uol.com.br/o-que-e/fisica/o-que-e-capacitor.htm