Properties of liquid helium II

Abstract

Summary The theory of the degeneration phenomena of an ideal Bose-Einstein gas is modified so as to make it more in accordance with the thermal phenomena of liquid helium II. At the lowest temperatures the specific heat can be brought in agreement with the experimental data when the plausible assumption is made, that an excitation energy is required for the conversion of a “condensed” molecule in a “moving” one. The abnormally thick surface films of He II are explained by a wave-mechanical treatment as being due to an additional zeropoint energy, which depends on the dimensions of the vessel and which predominates the effect of intermolecular forces in the surface layers. The flow phenomena in very thin layers and narrow capillaries are discussed; it is shown that the experiments point definitely in the direction of a slip of the liquid along the wall. The maximum slipvelocity as determined from the experiments must depend on the thickness d of the layer according to the formula vmax ∼ h/md. The same formula can be applied to the flow through narrow capillaries when d is replaced by the diameter of the capillary. Finally a proof is given that an excitation energy appears in the quantum mechanical perturbation theory of an ideal gas, when a small repulsive force between the molecules is introduced.