When a piece of aluminium wire of finite length is drawn through a series of dies to reduce its diameter to half its original value,its resistance will become ........ times.

Equal potentials are applied on an iron and copper wire of the same length. In order to have the same current flow in the two wires, the ratio $r_{\text{iron}} / r_{\text{copper}}$ of their radii must be (Given that specific resistance of iron = $1.0 \times 10^{-7} \, \Omega \cdot \text{m}$ and specific resistance of copper = $1.7 \times 10^{-8} \, \Omega \cdot \text{m}$)

How does the resistivity of a material depend on temperature? Write the empirical formula.

$A$ conducting wire of length $l$,area of cross-section $A$,and electric resistivity $\rho$ is connected between the terminals of a battery. $A$ potential difference $V$ is developed between its ends,causing an electric current. If the length of the wire of the same material is doubled and the area of cross-section is halved,the resultant current would be:

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)

If a conducting wire of length $L$ is uniformly stretched to double its length, then its conductivity becomes . . . . . . .