$A$ wire of resistance $x \ \Omega$ is drawn out,so that its length is increased to twice its original length,and its new resistance becomes $20 \ \Omega$. Then $x$ will be ........ $\Omega$.

$A$ wire $100\,cm$ long and $2.0\,mm$ diameter has a resistance of $0.7\,\Omega$. The electrical resistivity of the material is ...........$ \times 10^{-6}\,\Omega \cdot m$.

Wires $P$ and $Q$ have the same resistance at room temperature. When heated,the resistance of $P$ increases and that of $Q$ decreases. We conclude that:

Tungsten wire is used to make standard resistors because...

The resistance of a conductor at $20\,^{\circ}C$ and $500\,^{\circ}C$ is $20\,\Omega$ and $60\,\Omega$ respectively. At what temperature will the resistance be $25\,\Omega$?

Two wires $A$ and $B$ are made up of the same material and have the same mass. Wire $A$ has a radius of $2.0 \ mm$ and wire $B$ has a radius of $4.0 \ mm$. The resistance of wire $B$ is $2 \ \Omega$. The resistance of wire $A$ is . . . . . . $\Omega$.