Doubling Resistance of 1 Mile Copper Wire - 68 ohms

[dymand68]

Homework Statement

A 1 mile long copper wire has a resistance of 68 ohms. What will be its new resistance when doubling it over and using it as "one" wire

Homework Equations

?
R=V/current

The Attempt at a Solution

unable to attempt, I know that when it is cut in half R=34 ohms

 

[Doc Al]

I know that when it is cut in half R=34 ohms

OK. More generally, how does resistance depend on length and cross-sectional area?

 

[dymand68]

inverse square rule?

 

[Doc Al]

inverse square rule?

No. Read this: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/resis.html#c2"

 

[dymand68]

the correct answer is 17 ohms...double width, 1/2 length =1/4 resistance?

 

[Doc Al]

the correct answer is 17 ohms...double width, 1/2 length =1/4 resistance?

That's right. As that site explains, the resistance is inversely proportional to the cross-sectional area (which gives one factor 1/2) and directly proportional to the length (which gives a second factor of 1/2).