Copper and silicon are cooled from $300 \ K$ to $60 \ K$. The specific resistance:

Explain how the resistance of a conductor depends on its dimensions.

The resistance of a wire is $20 \Omega$. It is stretched,so that the length becomes three times,then the new resistance of the wire will be (in $\Omega$)

The following figure shows cross-sections through three long conductors of the same length and material,with square cross-sections of edge lengths as shown. Conductor $B$ will fit snugly within conductor $A$,and conductor $C$ will fit snugly within conductor $B$. The relationship between their end-to-end resistance is:

What is the resistivity of a perfect conductor?

The specific resistance of a wire is $\rho$,its volume is $3\,m^3$ and its resistance is $3\,\Omega$. Then its length will be: