State what boiling point means.
Explain, in terms of molecules, why energy must be supplied to change a liquid at its boiling point into a gas.
To find the power of the electric heater, connect two meters in the circuit. One meter measures the current in the heater and the other measures the potential difference (p.d.) across it. On the circuit in Fig. 9.1, draw symbols to show the two meters used and where they are connected.
The current through the heater is $2.0\,\text{A}$ and the p.d. across it is $6.0\,\text{V}$. Calculate the heater’s power.
Calculate the thermal energy transferred to the liquid by the heater in $1.0\,\text{minute}$.
The specific latent heat of vaporisation of the liquid is $9.0 \times 10^{5}\,\text{J kg}^{-1}$. Calculate the mass of liquid that changes into vapour each minute.
The piston can move freely inside the cylinder. As the liquid boils, the piston is driven upwards in the cylinder at a constant speed. The volume of the gas immediately above the liquid increases. Discuss whether the upward force on the piston changes as the piston moves upwards at constant speed.