Example.$\mathrm{.}12.$A cylinder of internal diameter. $0\mathrm{.}50$ m contains air at a pressure of $7$N$/$mm $^2($gauge$).$ If the maximum permissible stress induced in the material in $80$ N$/$mm $^2$ find the thickness of the cylinder...A cylinder of internal diameter. $0\mathrm{.}50$ m contains air at a pressure of$7$N$/$mm $^2($gauge$).$ If the maximum permissible stress induced in the material in $80$ N$/$mm $^2$ find the thickness of the cylinder