The graphic shows a truncated cone. The diameter of the cone changes from d_1 to d_2 along the x-direction.

Edit and compile if you like:
% Truncated Cone% Author: Mathias Magdowski\documentclass{article}\usepackage{tikz}\usepackage[active,tightpage]{preview}\PreviewEnvironment{tikzpicture}\setlength{\PreviewBorder}{10pt}%\usetikzlibrary{calc}\usepackage{amssymb}\begin{document}\begin{tikzpicture}\draw[dashed,color=gray] (0,0) arc (-90:90:0.5 and 1.5);% right half of the left ellipse\draw[semithick] (0,0) -- (4,1);% bottom line\draw[semithick] (0,3) -- (4,2);% top line\draw[semithick] (0,0) arc (270:90:0.5 and 1.5);% left half of the left ellipse\draw[semithick] (4,1.5) ellipse (0.166 and 0.5);% right ellipse\draw (-1,1.5) node {$\varnothing d_1$};\draw (3.3,1.5) node {$\varnothing d_2$};\draw[|-,semithick] (0,-0.5) -- (4,-0.5);\draw[|->,semithick] (4,-0.5) -- (4.5,-0.5);\draw (0,-1) node {$x=0$};\draw (4,-1) node {$x=l$};\end{tikzpicture}\end{document}
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