$A$ 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 ............. $\text{cm}$.

$A$ conducting wire has length $L_1$ and diameter $d_1$. After stretching,the same wire's length becomes $L_2$ and diameter $d_2$. The ratio of resistance before and after stretching is:

In order to increase the resistance of a given wire of uniform cross-section to four times its value,a fraction of its length is stretched uniformly until the full length of the wire becomes $\frac{3}{2}$ times the original length. What is the value of this fraction?

For metals,is the temperature coefficient of resistivity positive or negative?

The temperature coefficient of resistance of a resistor wire is $0.00125\,^{\circ}C^{-1}$. At $300\,K$,its resistance is $1\,\Omega$. At what temperature in $K$ will its resistance be $2\,\Omega$?

Two wires of equal length and equal diameter and having resistivities $\rho_1$ and $\rho_2$ are connected in series. The equivalent resistivity of the combination is . . . . . . .