Given:
internal radius = 4cm
External radius = 6cm
Height = 20cm
Curved surface area of the external surface
The formula for the curved surface is:
[tex]\begin{gathered} =2\pi rh \\ \text{Where r is a radius} \\ \text{and h is the height of the cylinder} \end{gathered}[/tex]
Hence, the curved surface area:
[tex]\begin{gathered} C\mathrm{}S\mathrm{}A\text{ of external surface = 2}\times\pi\times6\times20 \\ =753.982cm^2 \end{gathered}[/tex]
Curved surface area of the inner surface:
[tex]\begin{gathered} C\mathrm{}S\mathrm{}A\text{ of inner surface = 2 }\times\pi\times4\times\text{ 20} \\ =502.654cm^2 \end{gathered}[/tex]
The total surface area of the tube :
The total surface area can be found using the formula:
[tex]\text{Total Surface area = }2\pi(R^2-r^2)\text{ + }2\pi h(R\text{ + r)}[/tex]
Where R is the radius of the external surface and r is the radius of the inner surface
Hence:
[tex]\begin{gathered} \text{Total Surface area = 2}\times\pi\times(6^2-4^2)\text{ + 2}\times\pi\times20\times(6\text{ + 4)} \\ =\text{ }1382.3cm^2 \end{gathered}[/tex]
