If $n, e, \tau$ and $m$ represent electron density,charge,relaxation time,and mass of an electron respectively,then the resistance of a wire of length $l$ and cross-sectional area $A$ is given by:

The resistance of a wire is $5 \Omega$. Its new resistance in ohm,if stretched to $5$ times of its original length,will be:

The variation of applied potential and current flowing through a given wire is shown in the figure. The length of the wire is $31.4 \, cm$. The diameter of the wire is measured as $2.4 \, cm$. The resistivity of the given wire is measured as $x \times 10^{-3} \, \Omega \cdot cm$. The value of $x$ is . . . . . . [Take $\pi = 3.14$]

$A$ strip of copper and another of germanium are cooled from room temperature to $80\, K$. The resistance of

$A$ copper wire of length $L$ and diameter $D$ is to be reshaped into another wire so as to have minimum resistance. For this,we should:

The length of a hollow tube is $5\,m$,its outer diameter is $10\,cm$,and the thickness of its wall is $5\,mm$. If the resistivity of the material of the tube is $1.7 \times 10^{-8} \,\Omega m$,then the resistance of the tube will be: