Physics Help :-)

[Androme]

I've just been given an experiment assignment:

"When lightning strikes a building the reslts can be very dramatic. The current in the bricks may cause considerable heating of the bricks followed by rapid expansaion and failure of the structure. An engineer investigation this effect wishes to know how the electrical resustance of a house brick changes with temperature.

Design a laboratory experiment to investigate how the resistance of a house brick varies with temperature in the range of 20 degrees C and 800 degrees C. The resistance of the brick is very high. The brick is of a non-uniform shape and the resistance is to be measured across the end faces of the brick.

Write the procedure to be followed, steps taken to achieve a measurable current through the brick, how to attach the connecting wires to the faces, how the brick would be heated & how the temperature of the brick would be measured..."

The points such as safety precautions I already know.

I have fished around google for some time now. I found some other bloke asking the same question on another forum but the reply he has been given looks like bollocks.

I say this because I was looking through an old A-Level book, I found something on measuring resistance on a material with high temperatures - a Platinum Resistance Thermometer - with a range from -200*C to 1200*C which fits the 20*C - 800*C range of the brick. The book instructed that there is a problem as there may be large heat capacities but this is precluded because a Wheatstone Bridge is used. I looked at the diagram and description but it didn't exactly make sense. I guess that's how I can measure the temperature of the brick unless there's any brighter ideas.

As to how I connect the wires to the brick, I thought about drilling 2 holes into the brick or glueing 2 pieces of aluminium foil, 1 at each end-face and attaching the wire to that - I realise the effects on the results would be neglible but is this a sensible idea?

As for heating the brick itself, I thought about using an electric heater, based on a diagram in the same physics book, however, it had an insulating dish at the bottom, required oil or a liquid to be used and the galvanometer (micro-ammeter) and voltermeter only measured the power going through the heater - how this could be adapted to measure that of the brick in the same set-up is a tad bit tricking.

Thanks for any help

[Structural Integrity]

I know nearly nothing (more like nothing at all) about physics experiments, but I think you're doing it the right way.
Put the thermometer in a hole you drilled in the brick though and measure the temperature as close to the core as possible.
I'd also not use any glue for attaching any wires. Look up what the expected resistance of brick is at room temperature and determine if glue might have a significant impact if the glue causes the wiring to not connect to the brick properly. Also handy to determine what current you need to run through the brick to accurately measure the resistance.
Using a hole to put the wires in is a yes in my opinion to increase the contact area. Thereby, will any aluminium foil/glue hold out at 800 degrees?
I don't know about the electrical heater, but I'd take into account that you need to heat the brick as uniformly as possible. So that if you measure a core temperature of 800 degrees, the surface might be much hotter. Or cooler... Perhaps use two thermometers, one for the surface and one for the core.
Also, what are the effects of the size of the brick? I can imagine that a big brick, where the distance between the wires is larger, has a bigger resistance.

That's all my software mind can think of at the moment.

[1-X]

ITT Structural Integrity gives advice on Structural Integrity

[Knight Theamion]

what about the concrete used?

[Radical Edward]

take your parent's best oven drill a hole in the side. now take a length of electrical wiring, strip away the coating from the ends, thread the cable into the oven then tape (duct tape of course) the live and the neutral to either side of the brick and also connect a beefy voltmeter. Now turn the oven on to the desired temperature, et voila! do it at home.

the thermometer is a bit pointless really since if you use a decent heater and not a bunsen burner or something retarded, you should know the temperature. alternatively use an IR camera and look at the peak wavelength and calculate the temperature from the black body spectrum.

[xtrasyn]

I say just wait untill a phat lightning storm, go outside with a brick held high above your head, and stand in the middle of the field.

You will have to leave a sign with a self-adressed envelope and an instruction sheet saying:

´Dear fireman, policeman, infermary or whoever finds the heap of carbon I now am. Please remove the brick from the ashes where my abdomen used to be and measure the temperature. Please try to measure as close to the core of the brick possible. I do not really care if you would use imperial or metric system as long as it´s accurate. You can put the temperature on the form I prepared for you wich is in the envelope. Could you throw it in the box as soon as possible? Cheers, Androme2

P.S. Could you devine from the ion saturation of the ashes how high the current was?´

[demiGOD]

-A small brick.
-2 chicken wires, each at about 5 inches in length
-an Ohm meter, or a 500 VDC Megohmmeter
-a Pyrometer rated at 500 degrees F or a hi-temp Thermometer
-a candle or a lamp
-a low-torque drill
-protective gloves

Instructions:
Pre-Lab: Generate a hypothesis.

1] Drill small holes on each 'pole' of the brick deep enough to insert fully 2 inches of each chicken wire.
2] Drill a small hole on the top of the brick that will be deep enough to insert the Pyrometer or Thermometer probe
3] Securely insert chicken wires on each brick pole. Secure it sturdily with the other end of the chicken wires so you wires will resemble loops, or Mikey Mouse ears
4] At ambient temperature, generally at 77 deg F or 80 deg F, connect each Ohm meter (or Megohmmeter) lead onto Mikey Mouse ears on the brick poles, one lead on each loop, to measure the resistance across the brick (if Megohmmeter is used, crank Megohmmeter generator handle at 500VDC).
5] You will read somewhere around the MegOhms, or a very high KiloOhms reading, and this will be your resistance reading @ 77-80 deg F
6] Wear protective gloves and grab the Mikey Mouse ears and heat on top of a candle or lamp the brick for 5 minutes. Put the brick back down on your workbench and measure brick temp using the Pyrometer or Thermometer probe by inserting the probe on the small hole drilled on top of the brick.
7] If temp is not anywhere between 150-200 deg F, repeat step [6] of heating procedures until 150-200 def F is reached
8] When 150-200 def F is reached, repeat step [4] and log down resistance readings at 150-200 deg F and notice the drop in Ohms.
9] Conclude experiment with a statement that Temperature is inversely proportional to Resistance.


*Under no circumstances will you energize your poles!!!!
*Holding both leads of a Meghommeter while cranking the generator handle will cause electrical shock

[Androme]

Originally Posted by Radical Edward

take your parent's best oven drill a hole in the side. now take a length of electrical wiring, strip away the coating from the ends, thread the cable into the oven then tape (duct tape of course) the live and the neutral to either side of the brick and also connect a beefy voltmeter. Now turn the oven on to the desired temperature, et voila! do it at home.

this sounds like a good idea - the oven - the only problem with this would be achieving temperatures outside of the usual up to 300*C limit? as for the neutral & live - connecting it at one doesn't measure the current across the end faces does it? lastly, due to the high temperatures concerned, will the wires withstand them and not melt? will the voltmeter connected also withstand any heat passed on? will a high resistance voltmeter be needed and a galvanometer too?

demiGOD: - it's a tad bit confusing the beginning part of that - Radical's way seems a whole lot of easier

thanks all of you (inc. struct and xtra ;P )

[Radical Edward]

Originally Posted by Androme2

this sounds like a good idea - the oven - the only problem with this would be achieving temperatures outside of the usual up to 300*C limit?

as I said, a good oven.

as for the neutral & live - connecting it at one doesn't measure the current across the end faces does it?

one wire adhered to each face.

lastly, due to the high temperatures concerned, will the wires withstand them and not melt?

make sure you get some good wire then

will the voltmeter connected also withstand any heat passed on?

I never said to put the voltmeter in the oven.

will a high resistance voltmeter be needed and a galvanometer too?

no.

demiGOD: - it's a tad bit confusing the beginning part of that - Radical's way seems a whole lot of easier

thanks all of you (inc. struct and xtra ;P )

[xtrasyn]

Mine is the best

[Structural Integrity]

I wrote all that, and all I get is this little post scriptum saying "inc struct and xtra"...
I'm disappointed... no really... I'm disappointed in the internet. I atleast expected some positive rep.

[demiGOD]

Originally Posted by Structural Integrity

I wrote all that, and all I get is this little post scriptum saying "inc struct and xtra"...
I'm disappointed... no really... I'm disappointed in the internet. I atleast expected some positive rep.

Indeed all the suggestions were based on your pioneering. Except that you suggested applying current and energizing the poles which will definitely be calculable to attain the proper Ohms reading through a load, but unfortunately not very safe.

Reading resistance through a de-energized conductor using an ohmmeter or a megger is a safer option.

[Dead_Meat]

Dress meaple up in 100% nylon clothing, attach meaple to one sphere of a Van der Graff generator, which is in turn, wired to brick under test.

Place meaple in front of constantly changing porn, and, hey presto! Instant lightning!

[SYMM]

Poor meaple

[Structural Integrity]

I bet meaple will generate so much energy the brick will start to light up.

[elllllllllllm]

hi im doing this bitch of a coursework too. They all are brilliant ideas but in the c/w booklet it says "Your plan should be based on the use of standard equipment, apparatus, chemicals and other materials available in a school college or college science laboratory".

So basically it is impossible to do in class room conditions...

[Androme]

My tutor's helped me out so I no longer need help - ta all

[elllllllllllm]

how the hell did u attach a brick to the circuit im so stuck on that any ideas anyone?

[MrL_JaKiri]

Originally Posted by elllllllllllm

how the hell did u attach a brick to the circuit im so stuck on that any ideas anyone?

You get a brick. You put a wire leading to the positive end on one face of the brick. You put a negative wire on the opposing brick face.

Tadaa.

[flapjack]

if you run a current through the brick, wouldn't it heat up as well?

Measure current and voltage, measure temperature. Sounds easy enough (but probably isn't, I'll have to ask my physics teacher about that)

Oh and remember to stand on a rubber mat, preferably a couple of meters away from the brick, just in case you know

[MrL_JaKiri]

Originally Posted by flapjack

if you run a current through the brick, wouldn't it heat up as well?

If you run a current through anything bar a superconductor, it heats up. P = IV.

[JonnyBGood]

But what if you made the superconductor out of bricks! Aha, bet you didn't think of that one.

[Vaio]

Originally Posted by JonnyBGood

But what if you made the superconductor out of bricks! Aha, bet you didn't think of that one.

Don't they call them houses ?

~Vaio~

[JonnyBGood]

You'd be pretty ****ing cold if they were.

[Vaio]

Originally Posted by JonnyBGood

You'd be pretty ****ing cold if they were.

I am, it's f'kin freezing.

I've got the heating on and 4 cats sat on my feet. I'm still cold

~Vaio~

[Phalon]

These cats?

[Vaio]

Originally Posted by Phalon

These cats?

No, those ones have nipped out to fetch a pizza and some lager. They won't be long.

~Vaio~

[Phalon]

I miss my 'traditional' sundays

[MrL_JaKiri]

Originally Posted by Phalon

I miss my 'traditional' sundays

Ones that troll you then claim they never take anything seriously?