After Capacitor Discharge a few questions

[IssacBinary]

Hey, I am back, you might remember me from the reactance topic, anyway I managed to get there in the end, only due to you guys. Thanks for that.

This time its something slightly easier..

In an AC circuit, once the capacitor is fully charged, and the voltage switches direction, from that point on is the current in the whole circuit larger than just say the current if the capacitor wasnt there?

As you will have the current produced by the battery and also the charge / current released from the capacitor, so the both add together and the result is an increased current in the circuit. (Basically you could say its a circuit with double the source voltage if you wait for the capacitor to fully charge?)

If that's the case, if you had a large capacitor, after each reversal would the current in the circuit keep increasing, due to the increased voltage (battery + capacitor discharge) causing more and more charge being stored in the capacitor each time?

From my knowledge of reactance, the larger the capacitance the small the reactance is due to there being more area to store charge thus giving the capacitor less time to charge between cycles meaning less current is blocked. But, that makes it sound like with a larger capacitance more charge can be stored meaning it could charge up to more than the source voltage (which it cant). That I don't quite understand, I think I explained myself right?

Thanks
Matthew

 

[IssacBinary]

Anyone?

 

[IssacBinary]

Bump, sorry. But even just a "this is a stupid question" or something haha

 

[I_am_learning]

If you really need some response whatever that may be here it is
After quickly reading through the paragraph I couldn't understand what you are trying to say. Perhaps if you come with some specific examples along with illustrations, someone might get interested.
good luck.

 

[IssacBinary]

Ok, ill try again. But I don't know how to make it any simpler.

AC sources goes back and fowards / switching directions.

So in a circuit, AC source and a Capacitor. The capacitor charges up and has a voltage across it. Then the AC source switches direction and the capacitor discharges, then charges back up AC switches over and same thing happens again.

From when the AC source is first turned on, it generates a voltage and current say X once the capacitor has charged and then the AC switches direction, from then on is the total current in the circuit going to be larger than X as its going to be the charge released from the capacitor plus the current from the original source. It would also mean the circuit would have a larger voltage source? As its the AC source plus the voltage across the capacitor, effectively acting as a single larger voltage source?

If that is the case, if you had a large capacitor wouldn't the current and voltage keep increasing on each cycle as the charge stored in the capacitor would keep increasing (not for ever obviously) but a few more times / for a few more cycles due to the larger voltage and current in the circuit allowing more charge to be stored in the capacitor.

From my knowledge of reactance, the larger the capacitance the small the reactance is due to there being more area to store charge thus giving the capacitor less time to charge between cycles meaning less current is blocked. But, that makes it sound like with a larger capacitance more charge can be stored making it sound like it could charge to more than the source voltage? (which it can't right?). That I don't quite understand.

Let me know if that's any better, thanks

 

[Jiggy-Ninja]

During half of the alternation, the capacitor will discharge, and the current will be greater than what would have been without the capacitor there.

During the other half of the alternation, the capacitor will charge, and current will be less than it would have been if the capacitor wasn't there.

It all balances out in the end, there's no current runaway, and energy is conserved.

If the capacitor starts out charged initially, it will discharge through the voltage source until that balance point is reached.

 

[IssacBinary]

When you say about the current being less or more than if the capacitor wasnt there are you talking about the effect of the phase shift by the current? As in there would be no current then normally but due to the shift there is current?

Im talking about overall current in the circuit, would the discharge charge / current add together with the source current meaning there's a larger current flow in the circuit? Also as if the circuit has a larger voltage source.

 

[MisterX]

For a simple circuit where an AC voltage source, a capacitor, and a resistor are in series, the current will not be greater than if the capacitor was a short circuit. The magnitude of the current phasor will give the amplitude of the current waveform. That magnitude is equal to

[tex]\frac{|\tilde{V_{s}}|}{|R + Xc|}[/tex]

Xc is purely imaginary, so the value of the denominator will never be less than R, and thus the current will never be greater than if the capacitor was an open circuit.However this may not be the case for other circuits. For example, for a series RLC circuit at its resonant frequency, the capacitive and inductive reactances will cancel and the current will be[tex]\frac{\tilde{V_{s}}}{R }[/tex]

However if the capacitor is replaced with a short circuit, and the inductor remains, the magnitude of the impedance of the circuit will be greater than when the capacitor was present. Thus the current will be lower when the capacitor is replaced by a short circuit.So to answer your question of whether the current is larger than without the capacitor, it depends on what circuit and what you mean by the capacitor not being there (open or closed circuit).

 

[IssacBinary]

Ok so I understand total current would be I = V/Z,

But could someone explain what is flawed in my logic? Like an explanation to what is happening and why I am wrong rather than just equations as I like to understand something first and then understand the equations that make it happen.

Without a capacitor, if its not there, just AC and resistor. Capacitor just a short circuit instead for example.

 

[johncameron]

I am not understanding your point. What you are trying to explain. Capacitor has a charging and discharging characteristics. Its ok. But after that what is happening here. I am not able to satisfy with your question. Please explain properly.