Because the relationship between voltage and current in a capacitor is:
i = C*dv/dt
An instantaneous change in the voltage across a capacitor would require that the rate of change of the voltage (dv/dt) be infinite, and hence the current would have to be infinite.
For inductors, the relationship is:
v = L*di/dt
In order for the rate of change of current to be infinite (instantaneous change), the applied voltage would have to be infinite.
Infinite currents and voltages are hard to create and therefore instantaneous "response" is hard to obtain. :smile: Capisce?
capacitor does not allow instantaneous change in voltage because of stored electric field ...and inductor does not allow change in current because of stored magnetic field...
Regarding capacitors... there is always a certain amount of resistance inline.
If resistance could be zero, then the time constant would be zero, and capacitor action would be instantaneous.
The OP asked why the voltage across a capacitor can't change instantaneously. You are saying that "capacitor action" would be instantaneous. Just what do you mean by "capacitor action"? Do you mean the voltage across the capacitor? Please be more specific.
Yes, the charge on the capacitor.
The inrush of electrons into one plate, and the exit of electrons from the other plate. Either charging or discharging.
If when you say "inrush of electrons" you mean current, why not say current? If you mean something else, you should define it.
The current, which is the rate of change of charge into a capacitor, can change instantaneously, but the amount of charge on the capacitor can't change instantaneously. For the amount of charge on the capacitor to change in an infinitesimally small time (which is what is meant by instantaneous change), an infinite current would be required.
I guess I meant the amount of inrush and exit, of electrons.
I can go along with what you stated.
I realize the need to be careful how I phrase things, since we want accurate details, from several angles, to compile them in our minds and reach an intuitive understanding.
My perspective was expanded at finding Bill Beatty's website, and his articles on the nature of electricity and electrical components.
Example:
'CAPACITOR COMPLAINTS'
http://amasci.com/emotor/cap1.html
there is still some link missing in your post as per the previous one i feel that you are saying the response from the cap and induc may be instantaneous
can you pls clarify it
Explained in a very very elaborated way. For real understanding has to go through whole article reading carefully.In any circuit no change is reflected until there is no change in energy.
If we could make the resistance zero, then the RC time constant would be zero. Every capacitor would instantly charge or discharge.
If we could make the resistance zero, then the RC time constant would be zero. Every capacitor would instantly charge or discharge.
However it is not possible to make the resistance zero.
As for inductors...
Making resistance zero would cause current change to happen slower.
On the other hand, to make resistance infinite would not allow any current to flow.
I've read that even a piece of straight wire has a small amount of inductance. This means current changes can not occur instantly even in a plain wire.
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