Rate of flow of heat through a cylindrical rod is $\mathrm{H}_1$. The temperature of the ends of the rod are ' $\mathrm{T}_1$ ' and ' $\mathrm{T}_2$ '. If all the dimensions of the rod become double and the temperature difference remains the same, the rate of flow of heat becomes ' $\mathrm{H}_2$ '. Then $\mathrm{H}_2=$
A coil of area $12 \mathrm{~cm}^2$ has 250 turns. Magnetic field of $0.2 \mathrm{~Wb} / \mathrm{m}^2$ is perpendicular to the plane of the coil. The field is reduced to $0.1 \mathrm{~Wb} / \mathrm{m}^2$ in 0.1 second. The magnitude of induced e.m.f. in the coil is
For which of the following combinations of working temperatures, the efficiency of Carnot's engine is maximum?
A galvanometer of resistance ' $G$ ' is converted into an ammeter of resistance $\frac{\mathrm{G}}{40}$, by connecting a shunt ' $S$ ' to it. The part of main current passing through the galvanometer is