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Electricity Question for Unit 2 Edexcel

  • #1

Homework Statement


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.

The Attempt at a Solution


Is this something got to do with area ? R=pl/A ?
How do you explain this ?
 

Answers and Replies

  • #2
PeterO
Homework Helper
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Homework Statement


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.

The Attempt at a Solution


Is this something got to do with area ? R=pl/A ?
How do you explain this ?
There are 3 variables there: ρ , l & A you should consider/compare each of them.
 
  • #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 ?
 
  • #4
PeterO
Homework Helper
2,425
46
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 ?
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:

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