The variation of the resistance of a conductor with temperature is as shown in the graph. The temperature coefficient $(\alpha)$ of the conductor is:

$A$ wire of circular cross-section has an inner portion of radius $R$ made of a material of resistivity $\rho$ and is surrounded by an outer portion of thickness $R$ made of a material of double resistivity. Find the resistance of a length $l$ of such a wire.

The new resistance of a wire of $R \, \Omega$,whose radius is reduced to half,is

The positive temperature coefficient of resistance is for

The electric bulbs have tungsten filaments of same length. If one of them gives $60 \, W$ and the other $100 \, W$,then:

Two square-shaped metal plates $A$ and $B$ of the same thickness $(t)$ and of the same material are connected as shown in the figure. The side of $B$ is twice that of $A$. If the resistances of $A$ and $B$ are $R_A$ and $R_B$ respectively, then $\frac{R_A}{R_B}$ is: