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What material is a poor conductor of electricity?

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pablito
#1
Apr13-13, 03:49 PM
P: 4
Hello, I was wondering if anyone could tell me of an easily available (to a primary school teacher) solid material that conducts electricity, but noticeably poorly, so that it can be demonstrated and hopefully performed by 9 year olds.

To be exact, I want a solid material that can be connected to a 3v battery and bulb using crocodile clip leads so that...

a. the bulb will light up.
b. the bulb will be dimmer or brighter depending on the length of this semi conducting material in the circuit.

I had heard that lead and aluminium were poor conductors but when I experimented with a 1m aluminium rule and a strip of lead, there really was no noticeable change in bulb brightness at all. they may be poor conductors compared to copper, but I need something observable to a 9 year old's eyes.

Any ideas?

Thanks.
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technician
#2
Apr13-13, 03:57 PM
P: 1,506
In my teaching I have used pencil 'lead' as a semi - conductor.
Try different grade pencils 2B to 4H for example
milesyoung
#3
Apr13-13, 04:00 PM
P: 466
First thing that comes to mind is a linear potentiometer of appropriate size and resistance range. You should be able to remove the carbon element from it.

technician
#4
Apr13-13, 04:04 PM
P: 1,506
What material is a poor conductor of electricity?

To change the brightness of a bulb you will need a fairly small resistance....100ohms max.???
AlephZero
#5
Apr13-13, 04:11 PM
Engineering
Sci Advisor
HW Helper
Thanks
P: 7,115
Try a length of nichrome wire, from a scrap electric heater etc.
pablito
#6
Apr13-13, 04:17 PM
P: 4
Thanks guys, very helpful.

The pencil is perfect. I just cut one open and it shows a noticeable dimming from one end to the other, and we use pencils everyday so it's a familiar object and material, easily understandable to a 9 year old.

The linear potentiometer element may also be perfect, but not so immediate or recognisable, I don't have one or know where to get one (I looked on google, but the range is enormous when you don't know what you are looking for).

Is nichrome wire a better or poorer conductor?

Are there other options similar to the pencil that you can think of? Always good to have a range. It would have to be something that is a WORSE conductor than pencil lead (yes, I know it's not really lead), so that the dimming is really clear and hopefully a little less fragile that pencil lead, so children can make a dimmer switch of their own.

Thanks again, really helpful.
pablito
#7
Apr13-13, 04:20 PM
P: 4
Quote Quote by technician View Post
Try different grade pencils 2B to 4H for example
Do you happen to know which is the best insulator? Is there much difference between them?
technician
#8
Apr13-13, 04:22 PM
P: 1,506
You can try scribbling on paper with a pencil (2B?) to create conducting tracks.
It is possible to buy conducting paper and conducting putty but for young kids using pencil lead as a start takes some beating!!!!
technician
#9
Apr13-13, 04:26 PM
P: 1,506
The best conductors will be 6B, the best insulators will be 4H and so on.
Use wires with crocodile clips to make good connections to the pencil leads.
It is 'hit and miss'.......like all good experiments.
Kids love it
pablito
#10
Apr13-13, 04:27 PM
P: 4
I tried scribbling with a school pencil which sadly didn't work. Great idea. I like the sound of the putty too, I was going to look into that.
technician
#11
Apr13-13, 04:29 PM
P: 1,506
Let the kids try everything....try charcoal ( from art department) or barbecue!,,,,
The key is to use carbon in whatever form you can find.
Take an old zinc carbon battery apart and use the central carbon rod if you feel adventurous and your local health and safety do not object !!!!!
sophiecentaur
#12
Apr13-13, 05:42 PM
Sci Advisor
Thanks
PF Gold
sophiecentaur's Avatar
P: 12,132
I don't know where they got them from but the technicians at school had a supply of very thick pencil leads 4 or 5 mm thick. Excellent for resistance measuring and really strong. Carpenter' s pencils would be a robust alternative. A strong salt solution might get low enough resistance to light an LED with a 9V battery.
CWatters
#13
Apr13-13, 06:03 PM
P: 3,135
Google suggests that Playdough conducts electricity but I don't have any handy to try.

http://www.abc.net.au/science/articl...17/3479415.htm
Redbelly98
#14
Apr14-13, 06:57 PM
Mentor
Redbelly98's Avatar
P: 12,069
Quote Quote by pablito View Post
I tried scribbling with a school pencil which sadly didn't work. Great idea. I like the sound of the putty too, I was going to look into that.
Did you make a wide line, and retrace the line several times so that it is also really thick? Not that I know for sure this should work, but I wanted to throw that out there.

I recommend using an ohmmeter to figure out how much resistance you are really aiming for. If you measure the lightbulb's room temperature resistance, then its operating resistance will be about 15 times that value, since the lightbulb operates at a much higher temperature.

Once you have the lightbulb's resistance, then you know you want something that is comparable, or perhaps several times more resistive, to put in series and cause noticeable dimming.


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