A cylindrical rod is having temperatures $$\theta_1$$ and $$\theta_2$$ at its ends. The rate of heat flow is '$$Q$$' $$\mathrm{J}{\mathrm{s}}^{-1}$$. All the linear dimensions of the rod are doubled by keeping the temperatures constant. What is the new rate of flow of heat?

Two concentric coplanar circular loops of radii '$$r{ }_1$$' and '$$r_2$$' respectively carry currents '$$i_1$$' and '$$\mathrm{i}_2$$' in opposite directions (one clockwise and other anticlockwise). The magnetic induction at the centre of the loops is half that due to '$$i_1$$' alone at the centre. If $$r_2=2 r_1$$, the value of $$\frac{i_2}{i_1}$$

The Kirchhoff's current law and voltage law are respectively based upon the conservation of

The permeability of a metal is $$0.1256 ~\mathrm{TmA}^{-1}$$. Its relative permeability will be $$\mathrm{\left( {{{{\mu _0}} \over {4\pi }} = {{10}^{ - 7}}\,SI\,unit} \right)}$$ ($$\pi=3.14$$)