 #1
hidemi
 208
 36
 Homework Statement:

A highresistance material is used as an insulator between the conductors of a length of coaxial cable. The resistance material, which forms a hollow tube, has an inner radius a and an outer radius b, and the insulator provides a resistance R between the conductors. If a second insulator, made of the same material and having the same length, is made with double both the inner radius and the outer radius of the first, what resistance would it provide between the conductors?
The answer is R.
 Relevant Equations:
 R = density*(Length/Area)
Since both cylinders have the same material, this implies the density is the same. Length is also the same based on the question. We only need to compare the radii for resistance.
R2 = pi ((2b)^2  (2a)^2)
R1 = pi (b^2  a^2)
R2/R1 = 4, so my answer is C. But, the given answer is A.
Where did I do wrong?
R2 = pi ((2b)^2  (2a)^2)
R1 = pi (b^2  a^2)
R2/R1 = 4, so my answer is C. But, the given answer is A.
Where did I do wrong?