# Resistance, ohms

## 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

?
R=V/current

## The Attempt at a Solution

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

## Answers and Replies

Doc Al
Mentor
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?

inverse square rule?

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

Doc Al
Mentor
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).