The resistance of wire at $$0^{\circ} \mathrm{C}$$ is $$20 \Omega$$. If the temperature coefficient of the resistance is $$5 \times 10^{-3}{ }^{\circ} \mathrm{C}^{-1}$$. The temperature at which the resistance will be double of that at $$0^{\circ} \mathrm{C}$$ is
The electrons take $$40 \times 10^3$$ s to dirift from one end of a metal wire of length 2 m to its other end. The area of cross-section of the wire is $$4 \mathrm{~mm}^2$$ and it is carrying a current of 1.6 A. The number density of free electrons in the metal wire is
The current 'I' in the circuit shown in the figure is
Current density in a cylindrical wire of radius $$R$$ varies with radial distance as $$\beta\left(r+r_0\right)^2$$. The current through the section of the wire shown in the figure is