# What are capacitors for?

What are they for I've seen them everywhere... are they used to hold power?

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7 years ago
Pretty much. Capacitors are used to store energy, which is just about the same as power (unless you're a physicist - they get picky about stuff like that :).

They're basically used for two sorts of things:

1) temporary storage of electrical energy - for example, to keep volatile memory from being wiped while a portables device's batteries are being changed.

2) on AC (alternating current) circuits, capacitors can be placed so as to "condition" the alternating character of the current - just when the alternation takes place, and how fast, and stuff like that. This conditioning helps the electrical engineers get the right amount of power to the right place at the right time.
Just how and why this conditioning works is beyond me - I never got all that far with AC circuitry. But I do know that it's essential to things like Los Angeles sending power to heat Seattle homes in the winter and Seattle sending LA power to run air conditioners in the summer, or me being able to pick up the phone in Seattle and use a system based on electric signals to talk to my friends in LA.

Hope this helps.
7 years ago
Kazot!  If energy and power are the same thing, then you should be able to run a marathon just as easily as strolling the same distance over two or three days :-)
7 years ago
So then how come, if I don't pay the energy bill, the power company shuts off my electricity? ;)
7 years ago
Because the company delivers energy at a fixed rate, but you get billed for the time integral of that distribution :-)
kelseymh7 years ago
7 years ago
Um, kelsey, dude...
...if you take a look at that wikipedia article while pretending to know less about physics or electricity than, say, your neighbor's yappy little chihuahua - yeah, it really is that hard.
7 years ago
Getting the answer to the question "what are capacitors for" is in the third sentence -- it stores energy.  How it does that, and how capacitors work, is extremely complicated.  Asking the question without having expended any effort (compare, "Wikipedia's article about capacitors is really complicated.  What are they used for?") doesn't enamor me to becoming their private tutor.
7 years ago
I take your point (and I really don't mean to pick a fight). People who don't seem to realize that typing a four-word question into the "Ask It!" box is actually more work than typing one keyword into the Google search box annoy me, too.

But I'm also annoyed by Wikipedia articles with initial paragraphs full of  jargon and scientific over-specificity. The Capacitor article isn't as bad as some, but still:
"A capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric (insulator). When a potential difference (voltage) exists across the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force between the conductors."
I read that to the neighbor's chihauhau, and he ran away whimpering and hid under the sofa. :)

(Yeah, I could/should go in to Wikipedia and re-write those paragraphs that bother me. But I'm afraid that someone else would just change it back.)

Again, I don't want to pick a fight, especially with so generous and capable an 'Ibler & Answers Author as yourself.
Perhaps we could agree to differ on this one?
7 years ago
Greetings Gorfram. What I find more annoying are people that write "was that really so hard?" and attach a link, and then write four more comments saying they don't want to become anyone's private tutor, but proceed to pick apart everyone else's answers, when they could show off just as well by writing 'capacitors are used to store energy' (wait a minute, I think that was in there somewhere). Wow, that was a mouthful. I click on stuff to read answers and maybe learn something, and often find comments telling people to look elsewhere or do their own research. But I think folks might like to pick the brains of some of the (very) intelligent and educated among the community here, and get a far superior explanation than could be found anywhere else. Some answerers expend more time and effort telling others to look elsewhere than it would take to actually answer the question. And some are so compelled to comment on a question they don't like, they can't help but to put in their 'JFGI'. Maybe if they don't like the question, they should just ignor it, but I guess Pavlov's dog couldn't help itself either. I don't get it. Don't worry about it dude.
7 years ago

No worries, Caarnted - my mellow has survived entirely unharshed. :)

Let me make clear that Kelsey is a great guy, very much one of those intelligent & educated people here in whose brains the pickings are quite rich, and I respect the socks off of him (sorry about the cold toes, K :). He has 159 Best Answers as of this writing, one of them from me.

That said, back to beating the presumeably-dead-by-now horse of his comment. :)

For me, it's sort of a matter of "When Peeves Collide." Sure, the OP could more have clearly indicated any prior research on the question he might have done. But the OP also (appears, anyway) to have no particular base of knowledge in re electricity and magnetism with which to try to interpret the Wikipedia article.

Kelsey found the answer to the question "What is a capacitor for?" in the third sentence, and paraphrased that sentence for us as "it stores energy."

I've been itching to tear that first paragraph of the Wikipedia article apart since the moment I saw it. The direct quote of that 3rd sentence is:

"This field stores energy and produces a mechanical force between the conductors."

Let's say that my neighbors' chihuahua, who I know has no background in physics or electromagnetism, reads that sentence. Assuming that MNC is not completely flummoxed by the mystery of what the production of a magnetic force between the conductors might have to do with anything and just chooses to ignore that part, he's left with:

"This field stores energy."

What? Hunh? There's nothing about capacitors here. What "field"?
... Okay, it's probably the one mentioned in the previous sentence:

"When a potential difference (voltage) exists across the conductors, an electric field is present in the dielectric."

So that would mean:

"The electric field that is present in the dielectric when a potential difference (voltage) exists across the conductors stores energy."

But then what's a "dielectric"?
Let's see, there's something about that back in the first sentence:

"A capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric (insulator)."

So, the "dielectric" is an insulator that separates a pair of conductors, and those three things together are the capacitor. At least we're talking about a capacitor now. But putting this definition back into the sentence we're trying to understand:

"The electric field that is present in an insulator that separates a pair of conductors (a capacitor consisting of such a pair of conductors separated by a insulator) when a potential difference (voltage) exists across the conductors stores energy."

That is just not the same sentence as:

"A capacitor stores energy."

The capacitor isn't storing the energy in the Wikipedia version - it's the electric field doing the storing. And what's making the the electric field show up in first place, and what does it have to doing with there being a voltage across the conductors? Is the voltage across the insulator, too, or is it being applied sideways or something?

Apparently I remember the day my sophomore "Physics of Electricity and Magnetism" first started covering capacitance all too clearly. :)

But that's the basis of my whole stinkin' point here: it doesn't work to explain something in terms of what you already understand about it - not very well anyway. To really explain a thing, it has to be put in terms of what the other person doesn't understand about it.

Okay, end of wiki-prose-dissection/ramble/rant. I'm putting my peeve away and heading off to bed. :)

"A capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric (insulator). When a potential difference (voltage) exists across the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force between the conductors."

"A capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric (insulator). When a potential difference (voltage) exists across the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force between the conductors."

7 years ago
Cool. This is the actual best answer.
7 years ago
Thanks :)
But I'm not sure I strictly agree with you. I think my original answer (which the OP was kind enough to give Best Answer :) may be a better answer to the OP's original Question "What are capacitors for?"

The above works out to a pretty good answer to the question "What is a capacitor, and what does it do?", which isn't quite the same thing.
(To use Jack's example:
A rock is a solidified agglomeration of minerals. Rocks form plutons, tectonic plates, and a good deal of most mountain ranges.
Rocks are naturally occuring phenomena; and thus are not "for" any human purpose, any more than the rest of the universe is. Uses to which rocks have nonethless been put by humans include paperweights, tourist attractions in Central Australia, and ending a sentence with a plagioclase feldspar.)

BTW, sorry for the weird double-paste of the Wiki-text at the end of my post - that's what I get for not previewing. :(
7 years ago
Capacitors are indeed used to store electrical energy.  They are also used for blocking DC, for filters, for timing, for tuning, for lots of things really.

You know, I've seen rocks everywhere, and I've noticed many of them are heavy.

Rocks are used for making paper weights, right?
7 years ago
I meant paperweights.  I guess it's a compound word.  Although, the Wiki article didn't mention rocks used as paperweights, so maybe I was wrong about that.

I bet a rock could be used as a doorstop.
7 years ago
Why yes, yes they are!  Have you looked up any information on other things rocks are used for?  No, you haven't?  Oh, well, then I guess you're going to write your report about how the major industrial use of rocks is as paper weights.  Oh, and how rocks invented the light bulb, and discovered gravity...