A spherical thermocouple junction of 2 mm diameter (ρ = 8000 kg/m^{3}, c_{p} = 400 J/kg·K, k = 20 W/m·K) is placed in a gas stream with h = 100 W/m^{2}·K. How long will it take to register 95 % of the initial temperature difference? (answer in s)