Q.A wire of length 1m and radius 0.1 mm has a resistance of 100Ω . Find the resistivity of the material.
(a) 3.14 × 10-5 Ω-m
(b) 3.14 × 10-6 Ω-m
(c) 3.14 ×10-7 Ω-m
(d) 3.14 × 10-4 Ω-m
Ans: (b)
Sol: Use formula $\large R = \rho \frac{l}{A}$
$\large \rho = \frac{R A}{l} $