b
(b) Resistivity of the material of the rod \(\rho = \frac{{RA}}{l} = \frac{{3 \times {{10}^{ - 3}}\pi {{(0.3 \times {{10}^{ - 2}})}^2}}}{1}\)= \(27 \times {10^{ - 9}}\pi \,\Omega \times m\)

Resistance of disc \(R = \frac{{({\rm{Thickness}})}}{{({\rm{Area\, of \,cross }}\,{\rm{section}})}}\)

= \(27 \times {10^{ - 9}}\pi \times \frac{{({{10}^{ - 3}})}}{{\pi \times {{(1 \times {{10}^{ - 2}})}^2}}}\)\( = 2.7 \times {10^{ - 7}}\,\Omega .\)