ec2-18-216-239-46.us-east-2.compute.amazonaws.com | ToothyWiki | RecentChanges | Login | Webcomic We assign this the arbitary symbol: Sticky Equipment:
multimeter
chocolate
ruler, or micrometer for greater accuracy ;-)
thermometer
Method:
Measure room temperature (assuming chocolate is same temperature as room)
Choose a large piece of chocolate, preferably cylindrical, though oblong will do.
Measure dimensions and shape of chocolate piece.
Set multimeter to measure resistance using scale of greatest range.
Press probes into opposite ends of chocolate piece.
Adjust multimeter scale if necessary.
If resistance is too high, bite off half the piece of chocolate (mmmm).
Measure size and resistance again.
Experiment with different sizes to calculate resistivity for a given shape and size.
Conductivity is the inverse (isn't it?)
Results:
Using co-op fair trade dark chocolate, at 23 °C
shape: 1x4 square-based-pyramid sections, joined by 3mm high base size (l x w x h): 89 x 22 x 9 mm resistance along length: > 2 MΩ resistance along width in middle of chunk: > 2 MΩ resistance through height in middle of chunk: > 2 MΩ resistance through height between chunks: > 2 MΩ
Not very conclusive, though we can say that the resistivity is > 6.7e8 Ω/m and conductivity is < 1.5e-9 m/Ω
Now to write this up FastShow/CalifornianScientist?-stylie
Disclaimer: yes, I know I have ignored cross-sectional area
The above is a very poor way to measure the electrical conductivity of anything, though I admit that in the case of a material with as high a resistance as chocolate probably has the error will be relatively infitesimal. You should be using a 4-pt Kelvin probe approach, though it does need rather more apparatus:
Equipment:
Variable power supply (0-30V, 0-5A will do)
Two multimeters
cables
Vernier Callipers, since a micrometer is just awkward to use
thermometer if you really care
Method:
Connect a Kelvin Probe circuit with a multimeter in ammeter mode in series with the chocolate. Some conductive tape may be necessary to get a good electrical contact.
Apply a potential across the chocolate. Measure the size of this potential with the other multimeter, in voltmeter mode.
Measure the potential drop across two intermediate points in the chocolate with the multimeter in voltmeter mode. Make sure the cross-section of the chocolate in this region is relatively uniform
The resistance in this region is the ratio of the potential drop to the current being carried.
Measure the cross-sectional area and the distance between the probes with vernier callipers. The resistivity is the the product of the resistance and the cross-sectional area divided the distance between the probes. Conductivity is the inverse.
This is unlikely to work because the resistivity is going to be >10MOhmm and most multimeters can't read currents less than microamps.
You forgot the most important step in the experiment. Once finished testing resistance of choc bar, eat it. ^_^ --Tsunami I have a Megger somewhere lying around that could possibly work. It can measure really very high resistances. You'd probably be best getting a thin slice of chocolate, like from Lindt or something and then clamping it between two metal plates. Of course, that may make the chocolate taste a little funny for Tsunami's suggestion afterwards. --Admiral
[This] is how to measure the resistance of chocolate. You need a calibrated variable resistor capable of massive resistance, a bunch of massive (known) resistors and some decent copper wire. It's essentially a potential divider, comparing a pair of different resistances (one known, one unknown); you make the whole thing work by balancing it to 0, making it nicer than a potential difference approach. --Requiem
That isn't likely to be as accurate as a Kelvin 4-pt approach because of the massive rectifying contact resistance between the chocolate and the wires. --SF
IIRC you can get really good analogue methods of measuring zero p.d or current that don't work so well if you're trying to measure a finite p.d or current; what you're gaining on the swings you're losing on the roundabouts. I guess you could create some sort of conductive chocolate and use it for your wires so as to get less of a problem here... --Requiem
![[Home]](/img/text_logo.jpg){kind=logo}
ElectricalConductivityOfChocolate