The length of the wire is doubled. Its conductance will be

In the following diagram,the lengths of wires $AB$ and $BC$ are equal,but the radius of wire $AB$ is double that of $BC$. The ratio of the potential gradient on wires $AB$ and $BC$ will be (wires are made of the same material):

Resistance of a wire at $0^{\circ} C, 100^{\circ} C$ and $t^{\circ} C$ is found to be $10 \Omega, 10.2 \Omega$ and $10.95 \Omega$ respectively. The temperature $t$ in Kelvin scale is $\qquad$

Two metal wires of identical dimensions are connected in series. If $\sigma_1$ and $\sigma_2$ are the conductivities of the metal wires respectively,the effective conductivity of the combination is

The temperature coefficient of resistance at $0\,^{\circ}\text{C}$ is $\alpha = 0.00125\,^{\circ}\text{C}^{-1}$. At a temperature of $25\,^{\circ}\text{C}$,the resistance of a conductor is $1\,\Omega$. Find the temperature at which the resistance becomes $1.2\,\Omega$.

$A$ metal rod of length $10 \text{ cm}$ and a rectangular cross-section of $1 \text{ cm} \times 0.5 \text{ cm}$ is connected to a battery across opposite faces. The resistance will be . . . . . . .