# Capacitors dielectric

Discussion in 'General Electronics Chat' started by Chassis, Apr 21, 2015.

1. ### Chassis Thread Starter New Member

Apr 21, 2015
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Good day.can someone please explain to me how does current flow through a capacitors dielectric.I'm confuse as I know the dielectric is a insulator

2. ### Jony130 AAC Fanatic!

Feb 17, 2009
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1,116
Try watch this

And sometime ago I find this humorous drawing about capacitor.

3. ### Chassis Thread Starter New Member

Apr 21, 2015
6
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Jony thanks for your reply.I cannot view your 1st pic,but I can view the 2nd one that explains ac and dc.makes a lot sense.now how does a bulp light up when its connected to a circuit with a source via a capacitor.how does the current flow through,coz the bulb does light up,but your pic shows it should stop at the 1st plate.

4. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,993
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This is not a pic it is a youtube video
Code (Text):
This pic is a joke.
Capacitor current is proportional the rate of voltage change across it (proportional to how quickly the voltage across capacitor is changing).
The faster the voltage change (frequency of a AC signal is high) the large the current flow through capacitor (short at high frequencies).

I = C*dV/dt

This means that to sustain current through a capacitor the applied voltage must change. The more rapidly voltage changes the larger the current. On the other hand if voltage is kept constant no current will flow no matter how large the voltage.
Likewise if the current through a capacitor is found to be zero, this means that the voltage across it must be constant, not necessarily zero.

5. ### #12 Expert

Nov 30, 2010
16,705
7,358
Electrons do not flow through the dielectric. The force of the changing AC voltage pushes and pulls electrons on the other side of the dielectric. It is about electrons repelling each other. When electrons are forced against one plate of a capacitor, their charge pushes the electrons on the other plate away. When the AC voltage pulls electrons away from the first plate, the electrons on the other plate rush back in because they are being repelled less.

6. ### crutschow Expert

Mar 14, 2008
13,516
3,386
Do you understand how a capacitor stores charge when a DC voltage is applied?
In AC the process is similar except the capacitor is charged, and then discharged and charged in the reverse direction by the constantly reversing AC voltage.
This charge movement into and out of the capacitor is what appears as a current in the AC circuit.

7. ### nsaspook AAC Fanatic!

Aug 27, 2009
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I love EEVblog but Dave's video is the most waffling and confusing thing he's ever done. Charge is moved to and fro but not through the plates of the capacitor and in the material dielectric, molecules are reoriented (distorted from their fixed rest structure or possibly physically reoriented) in their relationship with other molecules by the electric field (from charge separation) of the plates to store energy. What actually moves through the capacitor is EM energy in fields. As usual a system approach is needed. The charges and fields work together to make it work. Isolating current instead of energy/work as a yes, no, how answer will be confusing.

Last edited: Apr 21, 2015
8. ### Chassis Thread Starter New Member

Apr 21, 2015
6
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(EM energy and fields) now I got it.thanks spook,and thanks for the link jony.it all makes sense now.