AC Voltage Applied To Capacitor

By Kunal Kapoor

In case of a DC circuit, a capacitor almost acts as an open circuit allowing no flow of current through it over longer durations. It only allows flow of current until the capacitor is charged. Once charging is complete, it offers very high resistance.

But in case of an AC circuit the capacitor equations are:

a capacitor circuit connected to an AC power source:

In case of above circuit, the Capacitor limits or resists the flow of current but does not offers extremely high resistance as in case with DC power source. 

If there is q amount of charge on the capacitor at any given time t. The instantaneous voltage v across the capacitor: 

According to Kirchhoff’s loop rule, the voltage equation is : 


hence the above equation becomes : 

Further simplifying the equation becomes: i

In above equation, oscillating current is equal to   or 

THus Capacitive Reactance is equal to 

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