How Does the Resistance of a Brick Change with Temperature?

[Gokul43201]

I expect that ionic conductivity would be the most important mechanism in brick.

Ionic conductivity may dominate the AC resistivity. The long time ionic contribution to DC resistivity would be small, I'd imagine.

Also, you don't really need electrical feedthroughs (thought they would be nice). One can easily leave the door open a crack (or drill a small hole if permitted).

Copper does not melt at 800C but it certainly softens a great deal, and will start to flow under weight if sitting at this temperature for a while.

 

[inha]

Ionic conductivity may dominate the AC resistivity. The long time ionic contribution to DC resistivity would be small, I'd imagine.

Since we're kind of on the topic can someone point me to an article or book with a segment on electric properities of insulators from a solid state physics point of view instead of electronics. I only have hook&hall at home and it doesn't go into the subject.

 

[the_fugitive]

kk erm guys, have got the same thing as u lot today and its in for friday, can anyone PLEASE offer a diagram of the experiment to help me out thanks, and oh anotehr thing, what sort of voltage do you think i should use? thanks

 

[Chirpy Chick]

Voltages

Does anyone have a clue what voltage to use? I know it must be high, but it's still got to be practical. How can I get such a high voltage anyway?

 

[inha]

If you have zero clue about what voltage you must use to get a measurable current you simply have to do trial runs with the experiment. I assume the assingment is more about how to do the experiment than giving concrete values. Can't you just write "measured with a sufficient voltage V which is determined via trial and error method"?

 

[pervect]

Just a few quick comments - it's very likely that one will be able to use a voltmeter as an ammeter for this application.

If one has a 2volt full-scale voltmeter witha 10 megaohm input impedance, it can be considered to be a 200na current meter with a 10 megaohm series impedance. Usually 10 megs is too high a series impedance to be useful for a current meter, but this case seems likely to be an exception.

If the brick starts to conduct too well at high temepratures, the series impedance can be reduced by adding a paralllel resistor (which will degrade the senistivity of the current meter, but this won't be a problem if the current is high).

While it would be theoretically possible to convert an old TV set to yield a 20,000 volt DC power supply, I wouldn't recommend it. Aside from the safety issues, it will probably be difficult to measure voltages much over 1000 volts with standard equipment. I'd try to keep voltages under 1000 volts unless there was no other way to do the experiment. You'd only get a factor of 20 in sensitivity from going from 1000 v to 20kv anyway.

I would suggest a transformer and a full-wave bridge rectifier circuit for the high voltage power supply if a 1000 volt variable power supply is considered to be "not standard equipment". Several approaches exist for varying the voltage (variacs are one).

Procuring an actual brick and attempting to measure it's resistance or IV curve at room temperature would probably be a good way to get a handle on what's needed.

A good experimenter would measure several points on the voltage-current curve of the brick, to see how linear it was.

The art department would probably have some sort of kiln - whether or not they'd let you drill holes in it is another issue.

 

[the_fugitive]

ok, so can someone give me an example of a diagram please! i beg you, coz its in for 2moro morning, adn an list of all the apparatus thanks

 

[inha]

what do you think there should be in the diagram? I think a lot of the details have been discussed here already. Give us your idea and let's then see if there's something to add or fix. it's way more instructive that way.

 

[miss17]

hi this is my idea

apparatus: digital voltmeter, ammeter, kiln, brick, thermocouple, copper wires, insulator, clamps

method
heat the brick in the kiln setting the temperature to about 100 degrees as a starting temperature of the expt.
set the apparatus while the brick is heated
after some time remove the brick from the kiln and measure the temperature of the brick with thermocouple
clamp the brick
close the switch n measure the current in ammeter n voltage in voltmeter
repeat the same procedure increasin the temperture by 100 degrees
note upto 8 readings
plot a graph to compare the results

 

[miss17]

the diagram should have eht, switch, ammeter, voltmeter parallel to the brick, brick clamped between the two copper plates n copper wires attached.

------ switch------e h t----------
i i
i i
i i
i i (i
ammeter i i copper wires
i i i
i i i)
i---plates brick clampped plates---i
i i
i i
i i
i i
i---------voltmeter-----------i

should b something like this m not sure

 

[miss17]

well tried drawing the diagram but got messed up! sorry

 

[inha]

continuous measurement would be more practical and accurate. if you could think up of a way to measure the temp and voltage simultaneously with no breaks in the heating you would get better results.

 

[taurinne]

hi!
im doing the same plan, could anyone show me how am i going to explain what you all said in form of a diagram, how to set up the apparatus maybe? and one more thing how would you heat up the brick? pls. i need to finish this by friday.

 

[typhoon]

it is probably a good idea to heat it up to about 850 degrees first and take measurements as it cools

i'm doing this plan too and it's for tomrrow lol

 

[gojita_lv4]

This is the procedure i though of :P

Firstly...i was thinking that u could use a High Tension Power supply (HTP) or a Extra High tension Power Supply (EHTP). That hsould be able to provide u with a large enough voltage to find the resistance.

Secondly you could use a thermocouple to measure the temperature, a thermometer won't do as it would burst. However a thermocouple can measure temperatures in excess of 800oC. Depends what u use.

As for a ammeter to measure the current, you could use a milliammeter as the current produced would be very small. Therefore a milliammeter would be able to measure the current.

The brick must be kept at a constant temperature each time it is increased and must be kept at the same temperature all over, therefore a kiln could be used. In a kiln the brick would be warmed evenly all over.

There you have it! lol, reply.