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# Why it does not change suddenly?

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#### Electronman

##### New Member
Hi,

What this means on real?:
The voltage (current) of a cap (inductor) does not change suddenly??

P.s why they show an inductor by letter "L" and not "I"? what "L" letter Stands for?

capacitors and inductors are having electric and megnetic field respectively that stores energy as per the value of the component and applied voltage(capacitor) or current(inductor).

when you apply a current (not voltage) to a capacitor it slowly builds up the voltage, you can not make it suddenly since it will make like a short circuit to the source.

similary when you apply a voltage to an inductor the current slowly increass, you can not establish an instant current through it. you may have experienced getting a shock when you break even a small current through an inductor, it wil try to maintain its current not changed suddenly by inducing high voltage to create a spark or a new path that gives you a shock.

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Ok thanks,
But If there is no resistor in series with a capacitor it charges up suddenly, so?!

yes it instantly draw a infinity current (short circuit) that we cannot feel. also the wiring will limit it, you can see in some power supplies where large capacitors are used, there will be a resistor and a relay to by pass it when its charged. its to prevent high load to the supply.

E=L*di/dt and i=C*dv/dt

Neither of those have a "resistance term" (ideal components), however, as mbarazeen points out, there are parasitic elements... capacitors have ESR (also ESL) and inductors have the resistance of the wire itself as well as inter-winding capacitance.

E=L*di/dt and i=C*dv/dt

Neither of those have a "resistance term" (ideal components), however, as mbarazeen points out, there are parasitic elements... capacitors have ESR (also ESL) and inductors have the resistance of the wire itself as well as inter-winding capacitance.

I do know the above formula bur I am not able to understand the physical meaning of what I told at my first post?
It seems to me that you are saying that what I told at first post is not due to the cap itself bur due to ESR and ESL, right??!!!

besides Why they show inductors by sign "L".

may be they alrady allocated "I" to current, not to confuse it may became as a standard "L" for inductors.

if any one knows historically they can explain better.

I do not know how "L" came to be used... maybe because "i" is used for current.

As for E=L*di/dt and i=C*dv/dt... they show that the current varies with time through an inductor and voltage varies with time in a capacitor.

Just like ohms law tells about the voltage/current relationship in a resistor, those two formulas tell us the voltage/current relationship in capacitors and inductors.

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Hi,

What this means on real?:
The voltage (current) of a cap (inductor) does not change suddenly??

P.s why they show an inductor by letter "L" and not "I"? what "L" letter Stands for?
Much of our physical world is governed by differential equations which relate physical quantities and their derivatives. "Changing suddenly" is an imprecise way of saying tha some real physical quantity has an infinite derivative. Many relationships would become impossible to deal with if we allow things to go to infinity. My question is if you had access to an infinite quantity of voltage, current, charge, energy, or whatever. How would you handle it?

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