Question

A hollow cylindrical conductor has length of $314\, m$, while its inner and outer diameters are $4 \, mm$ and $8 \, mm$ respectively The resistance of the conductor is $n \times 10^{-3} \Omega$.If the resistivity of the material is $24 \times 10^{-8} \Omega m$ The value of $n$ is ___

Answer 1

The correct answer is 2.
R=ρAℓ​, the cross-sectional area is π(b2−a2)
R=ρπ(b2−a2)ℓ​=3.14×(42−22)×10−62.4×10−8×3.14​
=2×10−3Ω
$\therefore$ n=2