instantaneous response of capacitors and inductors

[the moon is back]

hi, can anybody explain me why inductors and capacitors doesn't respond instantaneously?
i mean, i know that voltage across a capacitor cannot change instantaneously and current thro the inductor cannot change instantaneously, so why is that so?
i'l be waiting for your useful posts.
thank u!

 

[Magvitron]

they are energy storing elements. they will provide the energy for any instantaneous change.

 

[jeffrey samuel]

when a voltage is applied to charge a capacitor initially charge is 0 and it increases till it reaches maximum

when the supply is turned off the capacitor starts discharging based on the potential difference you know that ac signal has a maximum peak when this voltage is more than that of the capacitor voltage the discharge is stopped even during the negative half cycle

it starts to discharge only when the negative half cycle voltage goes below the capacitor voltage

thus there is a delay if the max voltage is less than the cap voltage the discharge is instantaneous

this applies to inductor also

 

[The Electrician]

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?

 

[jeffrey samuel]

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?

splendid explantion in deed

we can get some capacitors and inductors having very low response time

 

[peeyushsigma]

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...

 

[jeffrey samuel]

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...

yeah true but the response time can be altered to suit our need

 

[Raza]

In any circuit no change is reflected until there is no change in energy. This is the Natural Law that in any Capacitive circuit the Current lags the Voltage by 90° and in Inductive circuit the Voltage lags by 90°. Hence until the energy is not available no change can be effective. A very good explanation can be found here.

https://www.learnabout-electronics.org/ac_theory/ac_ccts_51.php

 

[BradtheRad]

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.

I have a Youtube video which shows animated simulations of capacitor action, under different waveforms.

It portrays current flowing in the wires. It portrays capacitors charging and discharging.

www.youtube.com/watch?v=eIWEU4pObJw

A coil presents immediate counter-EMF to any sudden change in applied voltage. It does this by way of impeding a change in current flow (the definition of inductance).

It has to do with the magnetic field of each wire resisting neighboring magnetic fields.

I have Youtube videos of animated simulations of coil behavior.

It shows flux fields building and collapsing. It shows changing emf.

Inductor behavior with DC:

www.youtube.com/watch?v=LVNxrN4jgvs

Inductor behavior with AC:

www.youtube.com/watch?v=Os3jF9UeMoE

 

[The Electrician]

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.

 

[BradtheRad]

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.

 

[jeffrey samuel]

if the electron inrush is at t=0 then when will the out rush from the plate be

 

[The Electrician]

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.

 

[jeffrey samuel]

i can say the response by memory devices can not instantaneous in short they have their own response time

as infinite current generation is not feasible

 

[BradtheRad]

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

 

[jeffrey samuel]

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

 

[BradtheRad]

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

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.

 

[Raza]

As I said earlier in my post #8, this is very clearly explained in the referred site address in post #15.

In any circuit no change is reflected until there is no change in energy.

Explained in a very very elaborated way. For real understanding has to go through whole article reading carefully.
Perfect " An electric charge is not stored in capacitor but an Electrical Energy ".

 

[The Electrician]

If we could make the resistance zero, then the RC time constant would be zero. Every capacitor would instantly charge or discharge.

A real capacitor having non-zero resistance can be modeled as a perfect capacitor in series with a resistance. Such an RC network (series resistor R and capacitor C) has a time constant. If R is non-zero, the capacitor is initially uncharged, and you apply a step of voltage by suddenly applying a voltage source of V volts, the capacitor voltage will increase in an exponential fashion. The initial current will be V/R amps, decaying exponentially.

If the resistance R decreases to zero, the time constant will indeed become zero, but the initial current will be V/R, where R=0; this initial current will be infinite. So, even though the time constant is zero the capacitor cannot instantly charge unless infinite current is available from the applied voltage source.

The explanation I gave in post #4 was specifically for an ideal capacitor, with associated resistance being zero.

The voltage across a capacitor cannot change instantly without applying an infinite current, regardless of what the time constant is.

 

[jeffrey samuel]

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.

that proves it

but each cap and induc has its own reactance which accounts for it
right

so the statement of 0 resistance in a ckt is hypothetical if i am not wrong

and there is a theoretical explanation only in your post as infinite resistance is yet to be achieved in real world