For Woopy: Explanation for why you lose 1/2 energy in a capacitor

[MileHigh]

Woopy:

A long time ago you were curious about why you lose one-half the energy when you connect two capacitors together.

The experiment:  Start with a 1000 uF capacitor A charged to 10 volts and 1000 uF capacitor B fully discharged to zero volts.  Then when you connect them together capacitor A is charged to 5 volts and capacitor B is charged to 5 volts.  When you make the before and after energy calculation the results are that you lost 50% of the energy.

So the questions are, why did you lose 50% of the energy and where did it go?

We can answer the question by doing some simple experiments.

Put a 10K-ohm resistor between the two capacitors and repeat the test.  You will find that the two capacitors are charged to 5 volts at the end of the experiment.

Do the test again, with a 1K-ohm resistor, and you will get the same result.
Do the test again, with a 500-ohm resistor, and you will get the same result.
Do the test again, with a 100-ohm resistor, and you will get the same result.

So, what is this experiment telling you?

The answer is that for any resistor value you will get the same result.  So when you make a direct connection between two capacitors, it's the resistance in the wires that does the same thing, and gives you the same result.

Where did the lost energy go?  The answer is easy, you lost 50% of the initial energy when the current flowed through the resistor and this produced heat.

In the case where you make a direct connection and the energy is lost in the resistance of the wires themselves, perhaps that still sounds strange.  However, even though the resistance is very low, the current is very high, and the formula for the power dissipated in a resistor is = (i-squared x R).  R is very low but i is very high.

So you finally have your answer.

MileHigh

[Magluvin]

Ok, well what if the resistance wasnt there? What if the caps and the leads and connections didnt have any resistance?

Cap A - 10v 1000uf discharged to Cap B - 0v 1000uf.  What will be the end result? ;]

And lets say that inductance is not in play also. ;] Just caps

Mags

[ibpointless2]

@ MileHigh


Hi milehigh, I understand what your saying but this is not what really happens in real world. I understand where you coming from, if one capacitor has 10 volts and you connect them both the voltage in both will reach a even point where one doesn't have more than the other. In real world testing i have found that this doesn't always happen. I've found that if you have one capacitor that has 800mV in it and another capacitor that has 20mV they won't meet in the middle and instead will self charge off each other. I know it sounds crazy but I've done the test and created threads about it.


Here's a video i made two years ago about this topic [size=78%]http://www.youtube.com/watch?v=wbn4vede2us[/size]


I also created a thread on the topic here too [size=78%]http://www.overunity.com/10216/parallel-charging-shows-overunity/[/size]


Capacitors can be very mysterious devices.

[IotaYodi]

I've found that if you have one capacitor that has 800mV in it and another capacitor that has 20mV they won't meet in the middle and instead will self charge off each other

Would the type and quality of the materiels along with the enviroment come into play on this?

[poynt99]

Ok, well what if the resistance wasnt there? What if the caps and the leads and connections didnt have any resistance?

Cap A - 10v 1000uf discharged to Cap B - 0v 1000uf.  What will be the end result? ;]

And lets say that inductance is not in play also. ;] Just caps

Mags

With resistive wire and non-ideal capacitors, each cap will have 5V.

With ideal wire and ideal capacitors (made from ideal conductors and ideal dielectric), each capacitor would have 7.07V.

However, does or will ideal conductors (zero resistance) and capacitors ever exist? Not likely.

But let's imagine that the day has arrived, and we have produced the ideal wire and capacitor (and inductor), and there is 0 inductance in the circuit. The time required to transfer the charge from the charged capacitor to the discharged capacitor would be infinitely small (0 seconds), and the current would be infinitely large. Can infinity really be reached?

With an "infinitely-large" current flowing for that "infinitely-small" amount of time, anything ferromagnetic or electrostatic within "infinite" distance from this "event" would be adversely affected by the infinitely-large electric and magnetic fields produced, including the iron in your blood.

In other words, you'd likely destroy not only yourself, but the universe as well.