A $1\mathrm{.}27-$cm diameter copper $($r$=8933$ kg$/$m$3,$C$=385$ J$/($kg$$oC$))$ sphere is heated in a convection furnace for a very long time so that its temperature becomes equal to the temperature of the air in the furnace at $260$oC$.$ Then, the sphere is removed from the furnace and is placed in a forced convection flow where the heat transfer coefficient$$h$$is $17$ W$/($m$2$oC$)$ and where the temperature is $38$oC$.$ If the thermal conductivity of copper is $400$W$/($m$$oC$),$ calculate the Biot number.