Please consider this MWE:



    \node (C) [cylinder,rotate=180,draw,minimum height=4cm,minimum width=1.5cm] {};
    \draw [thick,->] ([xshift=-20pt]C.top) -- ([xshift=-80pt]C.bottom) node {};
    \draw [thick] ([xshift=-80pt]C.bottom) -- ([xshift=-30pt]C.bottom) node {};

Actual tube

With your help, I want to draw:

What I want



This is so simple that even marmots can do it. (EDIT: compute the scattering angle.)



    \node[ellipse,draw,inner sep=0pt,minimum height=1.5cm,minimum width=4mm]
    \draw[name path=tube] (L.north) -- ++ (3,0) coordinate (A) node[above] {A}
    -- ++ (-40:2) coordinate (B)  node[right] {B}
    -- ++ (-80:3) 
    [rotate=10]arc(0:-180:0.75 and 0.2)[rotate=0] -- ++(110:2)  to[out=90,in=0] ++ (-0.5,0.5) 
    \draw[dashed] (A) to[out=0,in=110,looseness=1.3] (B);
    \path[name path=test ray] (L.center) -- ++ (4.5,0);
    \draw[ultra thick,-latex,name intersections={of=tube and test ray},
    mark=at position 2.5cm with {\draw[-latex] (-5pt,0) -- (0,0);}}}] 
    let \p1=($(intersection-1)-(A)$),\n1={2*atan2(\y1,\x1)} in
    ([xshift=-4mm]L.center) -- (intersection-1) -- ++ (\n1:2.5);
    \draw[dashed,very thick,blue] (intersection-1) -- ($(intersection-1)!3!90:(B) $) 
    coordinate (x3);
    \draw[dashed,very thick,red] (intersection-1) -- ($(intersection-1)!0.5cm!(B)$)
    coordinate (x4);
    \draw pic[draw=purple,angle radius=5mm] {angle=x4--intersection-1--x3}; 
    \draw pic[draw=black,angle radius=5mm,pic text=$\theta$,
    angle eccentricity=1.3] {angle=A--intersection-1--L};   

enter image description here

| improve this answer | |
  • 2
    Marmots are everywhere with nice answers! <3 – manooooh Oct 7 '18 at 0:47

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