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

At room temperature $(27.0^{\circ} C)$,the resistance of a heating element is $100\; \Omega$. What is the temperature (in $^{\circ} C$) of the element if the resistance is found to be $117\; \Omega$,given that the temperature coefficient of the material of the resistor is $1.70 \times 10^{-4}\; ^{\circ} C^{-1}$?

The cross-sections of wires made of the same material and having the same length are shown in the figure. What can be said about their resistances?

$A$ wire has a resistance of $10\, \Omega$. If its length is increased by $10\%$ by stretching,what will be the new resistance of the wire in $\Omega$?

Why does the resistivity of metals increase with an increase in temperature?

Choose the correct alternative:
$(a)$ Alloys of metals usually have (greater/less) resistivity than that of their constituent metals.
$(b)$ Alloys usually have much (lower/higher) temperature coefficients of resistance than pure metals.
$(c)$ The resistivity of the alloy manganin is nearly independent of/ increases rapidly with increase of temperature.
$(d)$ The resistivity of a typical insulator (e.g.,amber) is greater than that of a metal by a factor of the order of $(10^{22}/10^{23}).$