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Electrical resistance of brick
Hey. I have to 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. I know that resistance of a brick is very high so what fsd of voltmeter ammeter etc should i use?
Also, i need a reference in my write up to show where i got the info from ie resistance of a brick, could someone please help me out because i cant find anything on the net.
If anybody else is doing this exam and could point me in the right direction it would be much appreciated.
thanks, gray
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well that is a brick of a project. measurements of high resistences r usually done at very high voltages so that an appreciable current will pass and be measured. i suggest the loest ampmeter u can find that can appreciat at least 1 mA and u will probably have to develop like 100-1000 volts to make an appreciable current flow. ur best bet is to generate 12-24 volts AC (or more if u have the practical possibility) and the use a multiplying rectifier to get a high voltage and will also give u various voltages to experiment with. u could directly use the output of a 12 volt transormer (or whatever voltage u prefer) as that is already AC but if the design of the progect is also under examination i suggest building ur own AC generator for 12 volts as that qwill be looked on much more kindly but if however the esential is the calculation of the brick then just use a transdformer output. a word of warning don't think even once about usingthe mains directly as the AC source as this could be dangerous using a transformer is recomended as it isolates u could of course use a 240/240 isolating transformeru then just do the usual V/R = I setup for measuring resistance and make the necesary calculations. if u have to use anything higher that 400 volts make sure there is sufficient isolation. as for measuring a brick at 800 C i can only wish u good luck as i do not know how to dal with something that hot i do not know if the wire will melt. as for insulation at high temperatures u can use ceramic rings that also do well on high voltages.
if u need anymore tips my e-mail is on my website at www.thunderchild.digitalzones.com
Radionut, It just says 'house brick' so i'm guessing concrete...
Thunderchild, thanks you have helped a little bit but i've been told i must use a DC current.
So if anyone knows the resistance of concrete please help me a reference would be best. This is just for the planning excercise part of my practical exam which is why i need references and why i need to know what scale of 'meters to use etc.
the curent u measure with must be DC and if u r asked for a DC source then u must build an oscilator so that by transformer folowed by a rectifier or multiplying rectifier (that turns it into DC) the voltage is raised and made to DC again. a transformer can oly run on AC and if u put DC throught - BANG - also 50 Hz must be used with a normal mains transformer and with a multiplier rectifier the hight the frequenzy the better but even 50 Hz is fine but 1 KHz won't hurt.
I am an A-level Physics teacher and my students are also doing this coursework. I have come onto the internet to check there are no 'model answers' posted. You should be very careful about the questions you ask as, in my opinion, you are asking for help beyond the scope of what is allowed. This could easily constitute cheating and could result in you being disqualified from your Physics A-level. Your teacher will be able to answer any questions that do not go beyond the realms of what is allowed.
Hi, I'm doing the same coureswork but I disagree with the last comment. My teacher is as puzzled as I am.
With reference to the question I found this;
RTD�s employ the property that the electrical resistance of metals varies with temperature. They are positive temperature coefficient (PTC) sensors whose resistance increases with temperature. The main metals in use are platinum and nickel. The most widely used sensor is the 100 ohm or 1000 ohm RTD or platinum resistance thermometer.
RTD�s are the most accurate sensors for industrial applications and also offer the best long-term stability. A representative value for the accuracy of a platinum resistance is +0.5 percent of the measured temperature. After one year there may be a shift of +0.05�C through aging. Platinum resistance thermometers can cover temperature ranges from -200 to 800�C.
Hope it helps.
frankly ifind his a stupid exam. there must be something more useful and practical than putting extra high resistance and temperature together in a practical project. the only way todetermine if it will work is to build it and that could go beyould the studends pracal capacity due to costs and specific things necesary for the exsperiment like 3 testers one of which can measure extreme temperartues and a heat source to be acurately controlled so as correct values r recorded. what subject is this for ? i'd advise the person that thought it up to try the experiment him/herself first !
I'm doin this exam alos, but the thing i'm finding difficulty with is what to use as part of the circuit. The most obvious is copper, but this would not be able to maintain state at high temperatures. It needs to be a conductoer that has a melting point above 800 degrees, with as low a resistivity as possible. Any suggestions? Also does anyone know the resitivity of clay? NOT the resisitance,so that i can gauge what voltage i'll need to get an appreciable current flow through the brick.
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yea u go back and restudy
a brick probably has a resistance in the order of a giga ohm and i have never seen a comercial tester go above 2 megaohm. so the principal (ohms law) of R=V/I has to be applied using a high enough voltage to make an appreciable amperage flow. but as many have already stated this is difficult and frankly i think the person who thought the project up should go build it him/herself first and workout all the variables difficulties and costs. i'd just say build an ohmeter that can measure the cold brick that is a brick enough without the heat. and what does deerkirsty have to say to that ? u know how to solve it ? i don't request u post the answer to the project just tell us do u know how to do all this cause if u don't then well give the person that cooked it up a clonk on he head and start studying urself naturally u have to bear in mind the student practical/financial resources. and frankly for physics this is absurd we r going into electronics here and there r many other things in physics that student can be asked to do.
