円筒

\documentclass{tetsujsarticle}
\usepackage{tetsuryoku}

\tikzset{
  dim above/.style={to path={\pgfextra{
        \pgfinterruptpath
        \draw[>=latex,|<->|] let
        \p1=($(\tikztostart)!2mm!90:(\tikztotarget)$),
        \p2=($(\tikztotarget)!2mm!-90:(\tikztostart)$)
        in(\p1) -- (\p2) node[pos=.5,sloped,above]{#1};
        \endpgfinterruptpath
      }(\tikztostart) -- (\tikztotarget) \tikztonodes
    }
  },
  dim below/.style={to path={\pgfextra{
        \pgfinterruptpath
        \draw[>=latex,|<->|] let 
        \p1=($(\tikztostart)!2mm!90:(\tikztotarget)$),
        \p2=($(\tikztotarget)!2mm!-90:(\tikztostart)$)
        in (\p1) -- (\p2) node[pos=.5,sloped,below]{#1};
        \endpgfinterruptpath
      }(\tikztostart) -- (\tikztotarget) \tikztonodes
    }
  },
}

\begin{document}
  \begin{tikzpicture}

\draw[thick,-latex] (0,0,0) -- (4,0,0) node[anchor=north east]{$y$};
\draw[thick,-latex] (0,0,0) -- (0,7.5,0) node[anchor=north west]{$z$};
\draw[thick,-latex] (0,0,0) -- (0,0,5) node[anchor=south]{$x$};
\filldraw (0,6,0) circle (1.75pt) node[left,font=\small]{$P(0,0,b)$};

\fill[top color=gray!50!black,bottom color=blue!10,middle color=gray,shading=axis,opacity=0.25] (0,0) circle (2cm and 0.5cm);
\fill[left color=gray!50!black,right color=blue!50!black,middle color=gray!50,shading=axis,opacity=0.25] (2,0) -- (2,4) arc (360:180:2cm and 0.5cm) -- (-2,0) arc (180:360:2cm and 0.5cm);
\fill[top color=blue!90!,bottom color=blue!2,middle color=blue!30,shading=axis,opacity=0.25] (0,4) circle (2cm and 0.5cm);
\draw (-2,4) -- (-2,0) arc (180:360:2cm and 0.5cm) -- (2,4) ++ (-2,0) circle (2cm and 0.5cm);
\draw[densely dashed] (-2,0) arc (180:0:2cm and 0.5cm);

\draw[densely dashed] (-2,2.8) arc (180:0:2cm and 0.5cm);
\draw[densely dashed] (-2,2.6) arc (180:0:2cm and 0.5cm);
\draw[thick] (-2,2.8) arc (180:360:2cm and 0.5cm);
\draw[thick] (-2,2.6) arc (180:360:2cm and 0.5cm);
\draw[thick, orange] (2,2.6) -- (3,2.6);
\draw[thick, orange] (2,2.8) -- (3,2.8);
\draw[thick,-latex] (2.8,4) -- (2.8,2.8);
\draw[thick,-latex] (2.8,1.6) -- (2.8,2.6);
\draw[thick,latex-] (2.8,0) -- (2.8,1.2) node[above] {$z$};
\draw [dashed] (0,6)--(3,6);
\draw[thick,latex-] (2.8,6) -- (2.8,4.5)node[below]{$b-z$};
\node at (3.5,2.7) [anchor=east]{$dz$};
\node at (2,1.5) [anchor=east]{$\rho_v\ (C/m^3)$};
\draw (-2,0) to[dim above=$L$,color=orange] (-2,4) ;

\coordinate (vec1) at (30:1);
\draw[-latex,thick] (0,0) -- (vec1)node[midway,sloped, above, inner sep=1] {$a$};
\draw[ultra thick,-latex,blue] (0,6,0) -- (0,7,0) node[right] {$\mathbf{E}$};
     \end{tikzpicture}  
\end{document}