Three copper wires of lengths and cross-sectional areas are $(l, A)$,$(2l, A/2)$,and $(l/2, 2A)$. Resistance is minimum in

The resistance of a wire at $300 \, K$ is found to be $0.3 \, \Omega$. If the temperature coefficient of resistance of the wire is $1.5 \times 10^{-3} \, K^{-1}$, the temperature at which the resistance becomes $0.6 \, \Omega$ is: (in $K$)

$A$ cylindrical wire $P$ has resistance $10 \ \Omega$. $A$ second wire $Q$ has length and diameter half that of $P$. If the material of both the wires is same,then the resistance of wire $Q$ is (in $\Omega$)

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A:$ Alloys such as constantan and manganin are used in making standard resistance coils.
Reason $R:$ Constantan and manganin have a very small value of temperature coefficient of resistance.
In the light of the above statements, choose the correct answer from the options given below.

Write the equation representing the relation between resistivity and temperature.

$A$ wire of resistance $R$ and radius $r$ is stretched until its radius becomes $r / 2$. If the new resistance of the stretched wire is $x R$,then the value of $x$ is $\qquad$