Phase delay effect in a thermally homogeneous system heated periodically

The response of a thermally homogeneous system to a periodical heat inflow was studied. The results of the calculations and the experiment proved that the system's temperature changed periodically with a certain phase delay ϕ relative to the stimulus (heat influx) and dependent on the period T_h and the system's relaxation time τ, according to the equation tan ϕ = 2ωτ, where ω = 2π/T_h. This relationship can be used for determination of τ and the heat capacity of the system. The simple theory and experiment is a good example for understanding other relaxing processes of the exponential form and may be helpful to physics teachers at university level.