Experimental and theoretical study of adiabatic, intermediate, and isothermal oscillations in air

Abstract

We have used an electronic technique in R\"uchardt's experiment to obtain accurate measurements of oscillations in air confined to a finite volume at room temperature and pressure. The dimensions of the container are small compared to the wavelength of sound for the frequencies used (0.5 to 8 Hz). The nature of the oscillations depends on both frequency and amplitude. Below about 2 Hz, the oscillations undergo several changes as their amplitude decreases due to damping: (i) an initial adiabatic oscillation is followed by (ii) a transition (lasting one or two cycles) to intermediate oscillations which persist for several cycles, until the amplitude has decreased to a few mm, when there is (iii) a second, larger transition, (lasting two or three cycles) to (iv) isothermal oscillations which persist until the motion ceases. Above 2 Hz we cannot distinguish the initial adiabatic oscillation, and the oscillations are all of the same intermediate type. A theoretical model is presented for the effects of heat conduction on the bulk modulus of the gas and the relaxation time of the initial intermediate oscillations, and these are compared with measured values.