Electricity Question for Unit 2 Edexcel

[gangnamstyle]

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 ?

 

[PeterO]

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.

 

[gangnamstyle]

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 ?

 

[PeterO]

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?

 

[Nickie]

Yes, the potential difference between the top and bottom of the tree is related to the area of the tree. This is because the potential difference, or voltage, is a measure of the electric field strength. In this scenario, the lightning strike creates a strong electric field that travels through the tree, causing a current to flow. The current is the movement of electric charge, and it is directly related to the electric field strength.

The area of the tree comes into play because the electric field is stronger in areas with a smaller cross-sectional area. This is because the same amount of charge is being spread out over a smaller area, resulting in a higher electric field strength. Therefore, the smaller cross-sectional area at the top of the tree will experience a higher electric field and thus a higher potential difference compared to the larger cross-sectional area at the bottom of the tree.

Additionally, the resistance of the tree also plays a role in the potential difference. As you mentioned, the resistance (R) is directly proportional to the length (l) and inversely proportional to the cross-sectional area (A) of the tree. This means that the resistance will be higher at the bottom of the tree where the cross-sectional area is larger, resulting in a lower potential difference.

Overall, the combination of the electric field strength and the resistance of the tree results in a much larger potential difference between the top and bottom of the tree when a lightning strike occurs.