At room temperature $(27^{\circ} C)$,the resistance of a heating element is $50 \Omega$. The temperature coefficient of the material is $2.4 \times 10^{-4} { }^{\circ} C^{-1}$. The temperature of the element,when its resistance is $62 \Omega$,is $\qquad$ ${ }^{\circ} C$.

$A$ cylindrical resistor is connected to a battery with emf $5 \ V$. The resistance per unit length varies as $\rho(x) = \rho_0 \left(\frac{x}{L}\right)^\alpha$,where $\rho_0$ and $\alpha$ are constants and $x$ is the distance from one end of the resistor. The product $\rho_0 L$ is $10 \ \Omega$,where $L$ is the length of the resistor. If the thermal power generated by the resistor is $20 \ W$,then the value of $\alpha$ is:

The variations of resistivity $\rho$ with absolute temperature $T$ for three different materials $X, Y$ and $Z$ are shown in the graph below. Identify the materials $X, Y$ and $Z$.

At what temperature $(^oC)$ will the resistance of a copper wire become three times its value at $0^oC$? (Given: Temperature coefficient of resistance of copper at $0^oC$ is $\alpha = 4 \times 10^{-3} / ^oC$)

The power of a heater is $500 \ W$ at a temperature of $800 \ ^oC$. What will be its power at $200 \ ^oC$ in $W$? Given $\alpha = 4 \times 10^{-4} \ ^oC^{-1}$.

Two metallic wires of identical dimensions are connected in series. If $\sigma_{1}$ and $\sigma_{2}$ are the conductivities of these wires respectively,the effective conductivity of the combination is: