Capacitors are generally use for storing charges, they are use in both AC and DC circuits. Capacitors have different functions in different circuits, they are use for current regulation and filtering in DC circuits, Meanwhile, capacitors blocks DC and allows AC to flow through them, but why are they still used in AC circuits when they block current?
This is questions we have been coming across on the internet, so keep reading to understand how it works in AC and DC circuits! Capacitors in AC circuits.
When a capacitor is connected to an AC source it stores charges in the first cycle (when AC polarity changes from - to +).
But when the AC changes it first polarity to another the charges stored in the capacitor gets discharged quickly depending on the frequency of oscillation of the AC source.
During the changing of polarity of an AC the capacitor reacts against the change and this known as capacitance reactance (Xc).
Mathematically the Xc of a capacitor is calculated with this formular.
1/2πfc
where;
F Stands for frequency of the AC and it is measured in Hertz,
C stands for the capacitance measured in farad.
The more the capacitance of a capacitor the lesser the reactance that is why low capacitance capacitors like mica and ceramic capacitors are use in RF circuits, tesla coils, induction heater, inverters and tank circuits to fully convert DC to AC or radio frequency wave.
Example.
A 2uf capacitor is connected directly across a 60hz AC source find the reactive capacitance of the capacitor.
Solution.
Xc= 1/2πfc
= 1/2π×60×2uf
= 0.5×π×60×2×0.000001 =1.886×10^-04 ohms.
Capacitors in DC circuits. When a capacitor is connected directly to a DC power it stores charges until the capacitor's voltage is the exactly the same as the source it is connected to. When the capacitor's voltage is exactly the same as it source, it allows current to flow through it easily but it reacts against any sudden change in current or voltage, for this reason it is use in circuits for current regulation, and sometimes coupled together with an inductor for voltage regulation.
Why and how do capacitors blocks DC and allows AC to pass through them?
Firstly, Capacitors don't actually block current completely, when it is connected to a DC source it first draw current to itself until it voltage or current is exactly the same as it current source, at this time no current or little current is allowed to flow, but the time it takes to block DC depends only on it's capacitance. Therefore the more it capacitance the longer it blocks current. When it is fully charged it then allows current to flow across it because it can't allow electrons to it's plates at this time. Secondly, AC flows through capacitors easily because of it changing polarity. It charges capacitors very quickly at this point current flows through it, at high speed it discharges the capacitor when it polarity changes relative to it first state also at this moment it blocks current. Thus a capacitor connected to an AC will only allow one cycle to pass through it and this phenomenal is called half wave rectification.
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Basic Electronics