# A.C. Capacitor circuit problem

#### uzair

Joined Dec 26, 2007
110
In the A.C. circuit,whether the capacitor is charged when voltage changes its magnitude or when it changes its cycle?

#### uzair

Joined Dec 26, 2007
110
I have read the relevant topic and still confused about this following line:-"Remember, the current through a capacitor is a reaction against the change in voltage across it."I am trying to know that whether the "change" which is described in the line is the cycle change or just instantaneous change.If it is for the instantaneous change,why the current can not flow in a D.C. circuit?

#### Dave

Joined Nov 17, 2003
6,970
I have read the relevant topic and still confused about this following line:-"Remember, the current through a capacitor is a reaction against the change in voltage across it."I am trying to know that whether the "change" which is described in the line is the cycle change or just instantaneous change.
It is the instantaneous change, as denoted by the dE/dt term in the capacitor-current equation at the top of the page. If the instantaneous change in the voltage across the capacitor, dE/dt, is non-zero then for a capacitor of capacitance, C, then the current i will be a non-zero value.

If it is for the instantaneous change,why the current can not flow in a D.C. circuit?
In a DC circuit the capacitor acts like an open circuit - dE/dt $$\rightarrow$$ 0, therefore i $$\rightarrow$$ 0.

Dave