There are two wires of the same length and of the same material and radii $r$ and $2r$. The ratio of their specific resistance is

The lead wires should have

$A$ metal wire of specific resistance $64 \times 10^{-6} \, \Omega \cdot \text{cm}$ and length $198 \, \text{cm}$ has a resistance of $7 \, \Omega$. The radius of the wire will be ............. $\text{cm}$.

Dimensions of a block are $1 \, cm \times 1 \, cm \times 100 \, cm$. If the specific resistance of its material is $3 \times 10^{-7} \, \Omega \cdot m$,the resistance between the square faces is:

As the temperature of a conductor increases,its resistivity and conductivity change. The ratio of resistivity to conductivity

$I-V$ characteristic of a copper wire of length $L$ and area of cross-section $A$ is shown in the figure. The slope of the curve becomes