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Linear expansivity

  1. Apr 29, 2013 #1

    Eke

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    ever since i was taught this along with the other expansivities its been giving me trouble. the formula is for looking for the expansivity and then you'd be seeing questions telling u to look for L2.. and L2 is quite hard to find because the formula is not straight forward...

    please anyone,, how can i find L2 without all this stress
     
  2. jcsd
  3. Apr 29, 2013 #2

    jtbell

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    Staff: Mentor

    Exactly which formula are you referring to?
     
  4. Apr 29, 2013 #3

    Eke

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    l2-l1<divided by> l1(temperature2 - temperature1)= e divided by l1*final temperature... try writing it with a pen for better understanding
     
  5. Apr 29, 2013 #4
    You mean
    [tex]\frac{l_2-l_1}{l_1(T_2-T_1)}=\alpha[/tex]

    What is the question? "How to solve for l2" ?
     
  6. Apr 29, 2013 #5

    Eke

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    yeah yeah.. how to solve for l2... my text book gave me this formula..
    l2=l1(1+linearexpansivity<T2-T1>)
    let me write it in text...
    l2=l1(1+linearexpansivity...times <T2-T1>)
    and the formula is not as straight forward as it seems
     
  7. Apr 29, 2013 #6
    Actually this second form is the most common one.
    [tex]l_2=l_1[1+\alpha(T_2-T_1)][/tex]
    It follows from the first one from simple algebraic manipulation.
    I still don't see what your problem is.
    Do you want to plug in and find l2?
     
  8. Apr 29, 2013 #7

    Eke

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    yes.. thats the formula...
    first i plus l1 with 1 because multiplying it wouldnt make much sense..
    then i add the linear expansivity as told in the formula...
    then multiply all that with my final temperature...
    but still my answer is diff. from my text book...
    am i doing it wrong
     
  9. Apr 29, 2013 #8
    No, actualy what you say here does not make sense.
    You cannot add (in a meaningful way) a length with a pure number.
    I am afraid you need to brush up your algebra a bit. About precedence of operations and brackets.

    But here is how it may be done here (it's not the only way):
    Open the bracket and you will have
    [tex]l_2=l_1+l_1\alpha(T_2-T_1)[/tex]
    So find the temperature difference ΔT=(T2-T1) and them multiply this ΔT by α and l1.
    This will be by how much the length have changed.
    Finally add this to the original length, l1. And you will have l2.
     
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