What is a Capacitance - Page 1
Forum section: electronics / general

author: quantumfall
author_rank: Regular Contributor
timestamp: March 31, 2012, 06:19:55 pm
content: How dose it store electricity / energy?How do I visualize it if possible ?On an atomic level, is it just electrons forced in on top of whats there ? If so where do they fit in the atoms in the last shells ?It must supply electrons when discharging so I presume there are extra ones to the normal state, where are they stored ?Is it Voltage stress, I'm not sure how to visualize this ?Is it something different ?I would like a simple non math way to understand this As I'm not a math natural and anything past basic Algebra is over my head.Thats a lot of questions sorry.Thanks for any help.

author: IanB
author_rank: Super Contributor
timestamp: March 31, 2012, 07:52:12 pm
content: See here:http://amasci.com/emotor/cap1.html

author: quantumfall
author_rank: Regular Contributor
timestamp: April 01, 2012, 01:13:30 am
content: Quote from: IanB on March 31, 2012, 07:52:12 pmThank you for that.In the water analogy, I see that you get no more water in the "water capacitor" it stores energy in the stretched rubber. you do get more water on one side than the other though.In our plate capacitors I swop the stretched rubber to the electrostatic field in the dielectric , I'm not quiet picturing that as easy as the rubber analogy.The electrostatic field is not mechanical so no actual "Stretch" so no need for extra electrons to be packed in to increase the "pressure".Do electrons flow at all ?It's enough for me today, I can not quiet picture it.Do extra electrons fit in the negative side of the capacitor, if so where ? Is it in the outer shells of the atoms, between atoms ?Are these models of electricity too simple to really get any further with the real reality of it ?

author: IanB
author_rank: Super Contributor
timestamp: April 01, 2012, 02:12:37 am
content: Don't worry about the electrostatic field. Pretend you never heard such a word.The rubber membrane represents the gap between the two plates of the capacitor. It is an insulator so that no electricity can flow from one side to the other. When you charge up the capacitor, one plate accumulates more charge (water) and the other plate accumulates less charge (water) by an equal and opposite amount. A charge imbalance is created between the two plates.Unbalanced systems have a tendency to return to equilibrium, and this tendency is seen as a voltage between the two plates. The further from equilibrium the bigger the voltage difference. The voltage difference is similar to the tension in the rubber (this is why electric supplies used to be described as "high tension" and "low tension").The voltage difference between the plates creates an electric field that exerts a force on charged particles. It takes work to move charge against an electric force that opposes the movement. To do work on something requires energy. Therefore charging up a capacitor stores energy according to the amount of work required to force charge into it against the opposing force.

author: AntiProtonBoy
author_rank: Frequent Contributor
timestamp: April 01, 2012, 02:22:20 am
content: I have been watching this bloke's videos lately, and I found them very good. He covers mostly physics materials (I recommend you to check his channel if you're into that kind of thing), but his material also overlaps a lot of electronics related topics.

author: Rerouter
author_rank: Super Contributor
timestamp: April 01, 2012, 03:04:34 am
content: probably best not to go to far from the water analogy, as you charge up a capacitor, electrons either enter or exit the sides of the plates to equalise its plates voltage to what supplied at its pins,how the electrons are stored is due to a unique trait of metals, what is known as an electron cloud, metal atoms in a lattice let there outer shell electroncs float about, this is what makes them so conductive, but it also means that they can have electroncs displaced into it or removed from this cloud with less opposition than a single atom,this displacement of electrons is what causes the voltage differential across a capacitors plates,i think i shall stop there, before i get proven wrong,

author: quantumfall
author_rank: Regular Contributor
timestamp: April 01, 2012, 04:36:02 am
content: Thanks everyone, I will stick with the water analogy for now, I had it in my mind and it bothered me where the extra electrons sit as it were, seeing as there are only the same number of atoms in the plate charged or not. I can be happy with a cloudy explanation !"i think i shall stop there, before i get proven wrong" yes me too, I will get very lost if it all goes quantum.

author: Rerouter
author_rank: Super Contributor
timestamp: April 01, 2012, 06:36:02 am
content: well your already 90% of the way there if you can understand electron clouds in mettalic atomsyou started with the raw device a capacitor, and wondered how it worked, you then had a look at its makeup and the rules that govern it, plate area, dielectric strength, etc, and then started wondering on an atomic level how this worked due to science in highschools only teaching about electron shells, and i hope i filled you in on the partical level side of it,in short, always raises my spirits when someone goes digging deeper to actually try and understand there tools

author: IanB
author_rank: Super Contributor
timestamp: April 01, 2012, 09:36:29 am
content: Quote from: quantumfall on April 01, 2012, 04:36:02 amThe idea that electrons are always bound in atomic shells is a very simplified explanation of atoms. It turns out it is really not hard to rip a few electrons free. For example if you rub a balloon on your sweater to create a static charge, electrons are being moved from one surface to another creating a positive or negative charge. A negative charge is where there are "too many" electrons sitting on a surface, and a positive charge is where there are "too few". With a positive charge some atoms are inevitably left with insufficient electrons to balance the charge on the nucleus. It is puzzling to contemplate how that can be, but a positive charge can mean no other thing.

author: G7PSK
author_rank: Super Contributor
timestamp: April 01, 2012, 09:44:35 am
content: Interesting thought does the dielectric in a capacitor actually deform when charged. large ones certainly jump about when discharged and make quite a bang. I have been in a building where they used a medical laser upstairs every time a shot was fired it sounded and felt like the machine would hammer itself through the floor as the capacitor bank discharged, I have also held large power factor capacitors and you can feel them vibrating.

author: Rerouter
author_rank: Super Contributor
timestamp: April 01, 2012, 10:01:58 am
content: normally they will not distort, but when you start getting into large currents the magnetic fields generated in an electrolytics plates cause them to repel or attract significantly, depending on whether its drawing or being drained of charge,(the plates are wrapped against one another meaning at any specific point its: pos - neg - pos - neg, etc, amplifying this effect)

author: quantumfall
author_rank: Regular Contributor
timestamp: April 01, 2012, 11:04:01 am
content: Yes I can just about picture the electrons being on the plates but not connected to an atom but in a cloud so that helps thanks.It always amazes me how good a water analogy can be , given how different the subjects are.There is some very interesting stuff on the site IanB pointed too under the "Misconceptions" part.I've always been interested in how the atoms and electrons work but got stuck on the electrons only in shells, must be from chemistry classes it was a long time ago now.I have always just accepted that more charge was on one plate than the other, I just got to thinking how they could fit in, I could not see a clear answer.I understand that its just very hard to really picture things at that small a scale.I watched Feynman videos of his New Zealand lectures, he said that it's really screwy and he did not really understand it but the math worked and that was about as far as we had gotten then with Quantum stuff. I could have that wrong but thats the impression I had from him.http://vega.org.uk/video/subseries/8

author: quantumfall
author_rank: Regular Contributor
timestamp: April 01, 2012, 11:19:26 am
content: Quote from: AntiProtonBoy on April 01, 2012, 02:22:20 amThanks for these links will check them out today.

author: amyk
author_rank: Super Contributor
timestamp: April 01, 2012, 12:15:14 pm
content: The link to the post about how charging a capacitor does not increase the number of electrons within it reminded me of how many people have the same misconception about charging batteries.Understanding capacitance is really easy compared to understanding inductance.

author: IanB
author_rank: Super Contributor
timestamp: April 01, 2012, 04:40:02 pm
content: Here's the water analogy for an inductor:http://youtu.be/17_EArwjCdQIt's a boost converter (with an output smoothing capacitor) that boosts 6 ft of head to several times that, lifting water over a 14 ft wall in this demonstration.Unlike electrical boost converters that typically operate at 10's or 100's kHz, this one operates at a sedate 1 Hz.

author: G7PSK
author_rank: Super Contributor
timestamp: April 01, 2012, 05:42:56 pm
content: Quote from: IanB on April 01, 2012, 04:40:02 pmIts a ram pump, I renovated two ram pumps a few years back, they were manufactured in 1840. I would post some photographs but they are too big to go on this site. Changed my mind here a picture they are installed in a thatched building that was purpose built for them.