The resistance of a metallic wire becomes $8$ times when :

Space between two concentric conducting spheres of radii $a$ and $b$ $(b > a)$ is filled with a medium of resistivity $\rho$. The resistance between the two spheres will be

The conductivity of a conductor decreases with temperature because,on heating:

In order to quadruple the resistance of a uniform wire,a part of it is uniformly stretched so that the final length of the wire becomes $1.5$ times the original length. The fractional length of the stretched part is

What is the resistance of a cubic block of length $50 \, cm$ having a resistivity of $50 \times 10^{-8} \, \Omega m$?

The figure shows a rectangular block with dimensions $x, 2x$ and $4x$. Electrical contacts can be made to the block between opposite pairs of faces (for example,between the faces labelled $A-A, B-B$ and $C-C$). Between which two faces would the maximum electrical resistance be obtained? ($A-A$: Top and bottom faces,$B-B$: Left and right faces,$C-C$: Front and rear faces)