capacitors

[ROOP]

why current decreases while charging a capacitor?

[alpha2cen]

There are two different property device in the electric circuit, one is capacitor and the other is coil.

At the capacitor high frequency electromagnetic wave can easily pass, but low frequency wave can not do.

While, at the coil high frequency electromagnetic wave can not easily pass, but low frequency wave easily pass it.

[Xittenn]

why current decreases while charging a capacitor?

 

In a purely capacitive circuit there is no complete path for the current to flow through. Inside a capacitor there are plates separated by a dielectric or an electrical insulator that prevents current from flowing through. As a cause of this, charge builds up on each plate. This build up of charge produces a counter electromotive force canceling the force applied by the power source. This charge grows until the forces cancel each other and all current ceases to flow at all.

 

The time to charge a capacitor, or its counter emf at a given time is given by

 

[math] v(t) = V_0(1 - e^{\frac{-t}{RC}}) [/math]

 

generally speaking charging a capacitor will take five RC time constants(the accepted reality) :|

 

but the current in an AC circuit will be determined by it's capacitive reactance given by

 

[math] X_c = \frac{1}{2 \pi f C} [/math]

Edited January 17, 2011 by Xittenn