Teaching Capacitor to Kids - Suggestions?

that would require a huge CAP.

No - not with an low current LED and suitable series resistor. you can see the effects with less than 100uF.

The other way is to hook up an arduino to measure the charging and discharging waveforms on a cap and get the curves plotted out in real time by a processing app.

I'll probably get flamed for this, but...

I assume that these kids have already been introduced to the history of electronics, and have knowledge of the Leyden jar, correct? Perhaps they have even constructed one? Because otherwise, they will be getting an incomplete education on electronics.

Giving them a capacitor, showing that it can be charged up and discharged does nothing more than show them another "magic black box", the same as likely how they view their computer, their television, their cell phone, the family automobile - indeed, a myriad of devices that they (and most likely their parents) have no concept of the history behind, the people involved, the trials those people went through to develop it; in short, how it all really works in the end, and most importantly, why.

If they're lucky, and don't learn about the history of capacitors (and the science behind them) from you, then at best, the Leyden jar may be mentioned in passing in their history class (perhaps as a quick blurb next to discussion on Franklin's experiments with static electricity), and another mention on charges and insulators in their science classes (though both of these lessons together may be separated in time by a year or two) - and only the real lucky ones will see the connection between everything, and perhaps strive to know more.

I should hope we could do better by our kids educations.

/full disclosure: I am not a parent.

simple experiment to kids(10-13yr olds with no exposure to electronics)

Well maybe trying to relate a capacitor to something they already understand. Perhaps showing it as a spring, that when streached is storing energy from charging and when released, discharges that stored enegy?

Lefty

The water analogy is one of the best to explain a capacitor, say this:

A capacitor is like an water thank, when you connect it to a battery(the "water" supply) it will fill up of water, so if you disconnect the battery the capacitor will during a short amount of time still provide electricity("water") to the circuit(a simple resistor plus one led is a good one).
If you parallel two capacitors you will have the double amount of water and if you wire then in series you will have the same amount of water but the hose have the double of the size, it think that with your teaching skills that I dont have you can elaborate this a little bit more :wink:

that would require a huge CAP.

No - not with an low current LED and suitable series resistor. you can see the effects with less than 100uF.

You can see the effect on most electrical appliances that include a "power" LED connected directly to the supply. Worth pointing out...

I recommend high-voltage caps made from aluminum foil and plexiglass or similar. Charge them with some sort of electrostatic generator and compare the intensity of the resulting shocks. It gives a very solid understanding of the principles involved; you can play we size of plates and separation quite easily, and you can SEE and FEEL exactly what is going on. (SMALL-ish caps, mind you. A Leyden jar made from a single-serving yogurt container is probably about the maximum size you should deal with; you only want noticeable shocks, not painful ones.) (or you can compare size of sparks produced on discharge if everyone is all wimpy...)

I found a thing in my old physics book, and it included exactly this example, charge and then put a LED to it. It was explained as the "wallets for electricity", which I found easy to understand :slight_smile:

my old physics book ... included exactly this example, charge and then put a LED to it.

I feel old...

Don't forget the resistor, or this is a good way to demonstrate "how to destroy an LED."

(WITH a resistor you can also demonstrate RC time constants!)

  • without a resistor the cap will discharge silly quick, thus loosing the ohh feature

Thanks all! as always a great lot of information...

I found a thing in my old physics book, and it included exactly this example, charge and then put a LED to it.

This is what i think i will do... working on the values now..

The water analogy is one of the best to explain a capacitor

... Yes i will be using it..

I'll probably get flamed for this, but...

No mate.. you are welcome to throw in your thoughts.. isn't it a democratic forum? :wink:

Well the kids don't have any introduction to electronics(perhaps a bit to electricity) and my objective is to get them interested in the subject by exposing them to it and helping them experiment. I personally believe that if you teach the 'hows' and then go about the 'whys' at a later stage when everybody knows to use then the 'whys' become more relevant.. if not students might end up loosing interest half the way getting to know the 'whys'. I believe this is true here at the forum as well a lot of people first get the leds glowing, and then do projects and learn about the 'whys' as and when they run into problems during the projects. I would love to hear the others on this. I believe we have a lot of educators around here...

random safety thought, they do make non polarised electrolytic caps

ie http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P1159-ND

Talking of safety.. what are the conditions that can make a capacitor explode. I'm planning on using something rated 25volts with a 9volt battery. Is there a way this can explode under normal exploration by kids (reversing polarity, over charging, etc)?

they explode due to too much voltage being applied (25v on a 9v source is fine) or having its polarity switched

If you only use low capacity batteries they will just get warm and not explode when the polarity is reversed.

If you only use low capacity batteries they will just get warm and not explode when the polarity is reversed.

I've never intentionally tried it, but couldn't they potentially vent and leak (I don't consider venting to be the same as exploding, although exploding is the same as venting - just in a violent and quick manner!)?

9v batteries have an extremely low max current thanks to a very high internal resistance. They can't dump current nearly fast enough to cause (much) damage.

If you only use low capacity batteries they will just get warm and not explode when the polarity is reversed.

that clears it.. Next point..

Any interesting small project ideas? I was thinking of a small IR/LDR based intruder alarm (kids will have fun putting it up in their rooms) any other such suggestions which kids can relate to and apply in their own worlds?

pwillard had a great basic circuit

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1270733826/3#3

but that is more topics to cover

something else would be like

:-?

555-based "music synthesizer" ?
You can even replace the cap and convert it to an LED blinky, thereby demonstrating all sorts of thing about caps and sound...

Do you think kids would understand 555(10-13yr olds)? i'm just thinking of a few logic ics...anybody got any experience in teaching 555 to kids(personally all the modes might look daunting for kids)? I was thinking of a buzzer and a led to be moved around a wire.. you know the kind of stuff you find in exhibitions...some kind of a loop... any improvisation suggestions on this?

Do you think kids would understand 555(10-13yr olds)?

Well, we didn't analyze it at the transistor level till senior year of college, but if you've gotten them to understand resistors, capacitors, and switches, all you need to add is the function of a "comparator" (which is pretty obvious.) to understand basic operation of the 555. Use something like http://www.ecircuitcenter.com/Circuits/555_Timer1/555_timer1.htm as the basis converting the flipflop/transistor to a back-box "signal controlled switch (and leave out the spice/etc) The uninterested will be happy to treat the chip as a black box, and the few who are interested will leaving feeling like "holy crap, I sorta understand how the insides of a chip work!"

You could even "construct" a giant 555 timer using a kid or two to watching meter and throw switches to replace the chip contents. A fine, fine, use for those $2 harbor-freight meters...

Another possibility is a binary to decimal or decimal to binary converter (switches to lamps, using a diode array), but that's less useful...