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Electricity Question for Unit 2 Edexcel

  1. Aug 30, 2012 #1
    1. The problem statement, all variables and given/known data
    If lightning strikes a tree such that there is the same current through it as there was through the lightning conductor, then a much larger potential difference exists between top and bottom of the tree. Explain why this is so.

    3. The attempt at a solution
    Is this something got to do with area ? R=pl/A ?
    How do you explain this ?
     
  2. jcsd
  3. Aug 30, 2012 #2

    PeterO

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    There are 3 variables there: ρ , l & A you should consider/compare each of them.
     
  4. Aug 30, 2012 #3
    This is how I answered :

    The tree has a smaller area. From the equation ( R=pl/A ), when A is small, resistance is higher because they're indirectly propotional to each other. From equation ( V= IR ), when R increases, p.d. increases.

    Not sure whether correct or not. Otherwise, how would you answer it ?
     
  5. Aug 30, 2012 #4

    PeterO

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    I think the key is the ρ : the resistivity.

    Most lightning conductors are small in cross-section, and made of brass or iron.

    Most trees have a large cross-section, but are made of wood!

    Also, a lightning conductor is long enough to reach from the ground to the top of a tall building [they don't use them on short buildings]. How tall [long] is a tree?
     
    Last edited: Aug 30, 2012
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