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Find the resistance between the top and bottom faces of the cylinder

  1. Jun 22, 2009 #1
    1. The problem statement, all variables and given/known data

    A 361 g mass of aluminum (Al) is formed into
    a right circular cylinder shaped so that its
    diameter equals its height.
    Find the resistance between the top and
    bottom faces of the cylinder at 20◦C. Use
    2700 kg/m3 as the density of Al and
    2.82 × 10−8 OHM· m as its resistivity. Answer
    in units of
    OHM.

    2. Relevant equations
    R= raw *(L/A)
    D=(m/v)
    height = diameter .... therefore r will (h/2)
    V=pi*r^2*h

    3. The attempt at a solution


    what i did is that i solved for the height by substituting it in the density problem getting D(given)= M(given)/(Pi*(h/2)^2*h) .. which after solving is h= (1.444/(2700*Pi))^(1/3)
    after that i substitute it back into the resistance equation.


    Im stuck ad i eed your help please
    thanx i advance
     
  2. jcsd
  3. Jun 22, 2009 #2

    tiny-tim

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    Hi mba444! :smile:

    (have a pi: π and a rho: ρ and try using the X2 tag just above the Reply box :wink:)
    Well, that looks ok so far …

    what number did you get, and what did you get next? :smile:
     
  4. Jun 23, 2009 #3
    i got for h .. 0.0554m
    after substituting into the R equation i got 1.169e-7


    but my answer is wrong !!
     
  5. Jun 23, 2009 #4

    drizzle

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    I think you need to use the Callendar–Van Dusen equation [which is a relation between temperature and resistance]
     
  6. Jun 23, 2009 #5

    tiny-tim

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    I get your h, but not your R …

    how do you get 1.169e-7 ?
     
  7. Jun 23, 2009 #6
    ignore the previous value i think its a calculation mistake
    i calculated it again i got 3.65586e-8
    is it right ??
     
  8. Jun 23, 2009 #7

    tiny-tim

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    how did you get it?
     
  9. Jun 23, 2009 #8
    R= (2.82e-8)[(0.055)/(PI*(2*0.055)^2)]

    radius = 2* h
     
  10. Jun 23, 2009 #9

    tiny-tim

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    uhh? :redface: radius = h/2

    (and what happened to that π I gave you?)
     
  11. Jun 23, 2009 #10
    ya since in the question they told us that the height equal the diameter
     
  12. Jun 23, 2009 #11
    i really dont understand .. my home work is due today .. and i really feel lost
     
  13. Jun 23, 2009 #12

    Redbelly98

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    What values are you using for raw, L, and A?
     
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