AC voltage
applied to a capacitor
1) Consider a capacitor of capacitance (C) is connected to an alternating
source voltage
2) In capacitor, the AC current deposits charges on the plates of the
capacitor and after a each half-cycle discharge of the capacitor happens.
3) Again the capacitor get charges but this time, the direction of charging is opposite, and
applied current or voltage is also opposite.
4) The process repeats as the alternating voltage is periodically changes
it’s direction.
5) Suppose at any moment the charge on the capacitor is q. then potential due to this charge is
6) Now we know that
Therefore
Now the current flowing through the circuit is
Where
Therefore we see that the current in the circuit is leading
by 
or 
Then alternating voltage.
Phasor diagram of AC circuit
containing capacitance:
As we see the current is lead by or than the alternating voltage, in
an AC circuit containing a capacitance.
We see that
Where
is called the capacitive reactance. Capacitive reactance XC has same dimensions like resistance (ohm) in SI unit.
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