The thermo $e.m.f.$ produced in a thermocouple is given by the equation $E = 40\theta - \frac{\theta^2}{20}$,where $\theta$ is the temperature difference between the two junctions. The neutral temperature is ............. $^oC$.

$A$ thin-walled cylindrical metal vessel with a linear coefficient of expansion $10^{-3} \ ^\circ C^{-1}$ contains benzene with a volume expansion coefficient of $10^{-3} \ ^\circ C^{-1}$. If the vessel and its contents are heated by $10 \ ^\circ C$,the pressure due to the liquid at the bottom:

$A$ geyser heats water flowing at a rate of $2.0 \; kg$ per minute from $30^{\circ} C$ to $70^{\circ} C$. If the geyser operates on a gas burner,the rate of combustion of fuel will be $\dots \; g \min^{-1}$.
[Heat of combustion $= 8 \times 10^{3} \; J \cdot g^{-1}$,Specific heat of water $= 4.2 \; J \cdot g^{-1} \cdot {}^{\circ} C^{-1}$]

Water falls from a height of $500 \ m$. What is the rise in temperature of water at the bottom if the whole energy remains in the water? (Assume $g = 9.8 \ m/s^2$ and specific heat capacity of water $c = 4200 \ J/kg \cdot ^\circ C$)

Heat is being supplied at a constant rate to a sphere of ice which is melting at the rate of $0.1 \, g/s$. It melts completely in $100 \, s$. The rate of rise of temperature thereafter will be ........ $^\circ C/s$ (Assume no loss of heat.)

$A$ solid cube of mass $m$ at a temperature $\theta_0$ is heated at a constant rate. It becomes liquid at temperature $\theta_1$ and vapour at temperature $\theta_2$. Let $s_1$ and $s_2$ be specific heats in its solid and liquid states respectively. If $L_f$ and $L_v$ are latent heats of fusion and vaporisation respectively,then the minimum heat energy supplied to the cube until it vaporises is