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Electrical Resistance of a brick

  1. Mar 21, 2005 #1
    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 I'll need to use a high voltage, perhaps 5000V.

    The main problem i have is figuring out:
    1. How the brick is to be heated.
    2. How to measure the temperature of the brick.
    3. And how to heat the brick up without heating any of the connecting cables as that would just make the resistance appear to be higher once the values for the voltage and current are recorded.

    I thought about using a blow torch near the brick and heating it up, but then couldn't figure out how to measure the temperature, and how to maintain the temperature of the brick, and how to keep a fairly even temperature all the way round the brick.

    Any suggestions? Thanks.
     
  2. jcsd
  3. Mar 22, 2005 #2
    How about this use an oven that can be heated over the specified temperature range. Inside the oven have to copper rods that extend to the out side of the oven. Measure the resistance though the copper rods.

    Before performing out the experiment with the brick perform the experiment with a solid copper rod.

    Now you know the resistance of copper depending on temperature and length of the copper rod and can find the resistance of the brick knowing the length of copper rod used in addition to the brick.

    Make sure to use the same thickness of rod in each case otherwise the resistance would change.
    http://hyperphysics.phy-astr.gsu.edu/hbase/electric/resis.html#c2

    You can also check you results for copper against standard tables.
    http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/rstiv.html#c1
    http://www.8886.co.uk/ref/resistivity_values.htm


    To check or double check your temperature you could use a thermocouple.
    http://hyperphysics.phy-astr.gsu.edu/hbase/electric/tcoup.html

    Hope these ideas help or at least spur you on.
     
  4. Mar 23, 2005 #3
    Thanks...thats a very good idea and does solve alot of the problems :smile: .
    I didnt understand the thermocouple though :confused:. I think i know how it works, im just not sure how I could implement it into my circuit and design.

    I was also thinking, can't i just pass the current through the brick and heat it up that way. The higher the voltage that gets pumped in, the higher the resistance and thus more heating affect. However the only problem I see with this is that a very large voltage will be needed to heat it up to 800 degrees C. And the temperature is meant to be the variable, and voltage and current the measurements; as opposed to having the voltage the variable and the temperature and current the measurements - if that makes any sense.

    I got this idea from the introductory paragraph to my investigation is:
    "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- 800 degrees C. The brick has very high resistance, and a non-uniform shape, the resistance is to be measured across the length of the brick"
     
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