How Dc current flows from capacitor

[nikhil arora]

I know Dc current does not flow from capacitor.
But when it is just power on Dc current flows through it.
now when there is not electrical connection between capacitor plates how current can flow.
I remeber my class lecutures which say that there is displacement current rather then the current due to electrons. Displacement current is due to Electric fields between plates.

But I am not able to physicall visualize the situation here. can anyone here can explain this physically or mathematically.

 

[falmeshon]

think of displacement current like this.

you put one magnet on a table and push another magnet towards it. If you are trying to push towards a pole of the same polarity, the magnet that you are not pushing will begin to "displace" or move as you get closer.

In a similar manner, charges building up on one plate of the capacitor cause the charges on the other plate to move or displace an equal amount. The faster the charges build up, the faster the charges will displace on the other plate. So if we look at the capacitor as a whole, there is no current going THROUGH the capacitor, but current is going in and current is going out so we can effectively say there is current flow.

 

[nikhil arora]

and according to this theory how the currents stops.
i.e when both plates have equal charge then current stops and this can be called as the capacitor has attain the equilibrium.

Can u tell me how can i read more on this type theories.

for example
When two charge spheres having charge q on them and radius R and 2R and contact is made between them and after separating the charges on them will be q/3 and 2q/3.

I have the book resnick and krane but it does not have sufficient examples i am looking for more examples

can any one suggest me book which can help me in preparing such question of electricity and magnetism.

 

[falmeshon]

and according to this theory how the currents stops.
i.e when both plates have equal charge then current stops and this can be called as the capacitor has attain the equilibrium.

incorrect. plates will only have equal charges when the capacitor is totally discharged. when it is partially or full charged there is an excess of charge on one plate and a deficiency on the other. That is why there is a voltage across it.

current will stop flowing ONLY when the voltage across it is steady. Why? because the charge stored on the plate will no longer is adjusted (hence no displacement current) to reflect the voltage across it.

i would recommend some sort of physics textbook for you q about charge spheres.

 

[Brrain]

bi-polar vs polarized

is the concept the same for both polar/bi-polar caps?

 

[Nigel Goodwin]

Re: bi-polar vs polarized

is the concept the same for both polar/bi-polar caps?

Yes, it's for 'capacitance' not any specific type of capacitor.

As a matter of interest, capacitance is defined as "the property of a circuit to store energy in the form of an electro-static field".

 

[Styx]

its not actually DC current, it is exponential current, ie AC

DC does NOT flow through a capacitor

 

[nikhil arora]

For understanding such concepts I have to study Electrostatics and magnetism.

Which is good book or tutorial we can download.

 

[ljcox]

I suggest that displacement current is a "real current" even though there is no flow of charge carriers, reasons:-

1. Maxwell's equations indicate that the displacement current is proportional to the rate of change of the electric field, has the dimensions of current, and it generates a magnetic field identical to one that would be produced by a "real" current in a conductor. For example, consider a capacitor constructed from 2 parallel metal plates. When it is charging, the electric field between the plates is increasing in intensity. The changing electric field creates the displacement current which is said to flow between the plates and is perpendicular to them. The magnetic field is perpendicular to the current and the lines of electric flux.

2. Generations of physics teachers have taught that "real current" is the movement of charge carriers such as electrons. But I suggest that future developments may alter this viewpoint. Physicists from Einstein onwards (and possibly earlier) have been searching for the "theory of everything". I feel that, when this theory is devised, it may include a new definition of electric current.

As I understand it, the most promising contender for the "theory of everything" is string theory. So electric current may be a flow of strings. Such a current may be able pass through dielectrics such a vacuum, air, plastic, etc. The movement of charge carriers may be simply because they are being pulled along by the "string current". As an analogy, consider a river of clear, slowly flowing (ie. non turbulent) water. The current is virtually impossible to see unless there is a marker of some kind such as a floating leaf or a colouring of the water by a blob of dye, etc.