Circular sector

Question

I'm trying to draw a circular sector. The code:

\documentclass[tikz,border=5pt]{standalone}

\begin{document}
\begin{tikzpicture}[thick,font=\sffamily\Large]
\draw (0,0) circle (4cm);
\filldraw circle (1pt) node[below] {$O$};

%secteur
\draw[fill=blue!30, opacity = 1] (0,0) --  (220:4) arc(220:120:4) -- cycle;

%angle
\draw[<-, color = blue]  (220:1.2) arc(220:120:1.2) node[midway,left]{$\alpha$};

%L
\draw[latex-latex, color = red]  (220:4) arc(220:120:4) node[midway,left]{L};

%rayon
\draw[very thick,-latex] (0,0) --  (20:4) node[midway,above]{1};
\end{tikzpicture}
\end{document}

somewhat works but needs a few tweaks that I've been unable to do, namely remove the dark color that overlaps with the red color on the arc named L, make the center O just a little below and add a pointing arrow to the red arc.

Thanks for the help!

edit:

Thanks!

How can I add a pointing arrow named B like that:

I've tried \draw (-1.2,2.2) -- (-0.23,1.1) node at (-1.37,2.37) {$B$}; but guesstimating doesn't work

Answer 1

• I draw an arc instead of a circle at first to avoid overlapping, which leads to the "dark color".
• I use \path instead of \draw so that the outline of the arc is not drawn.
• I use the command you used to draw the arrow from O to the red arc.
• I use below=1ex to make O lower a bit.

Code:

\documentclass[tikz,border=5pt]{standalone}

\begin{document}
\begin{tikzpicture}[thick,font=\sffamily\Large]
%\draw (0,0) circle (4cm);
\draw (120:4) arc (120:-140:4);
\path[fill=blue!30, opacity = 1] (0,0) --  (220:4) arc(220:120:4) -- cycle;
\draw (220:4)--(0,0)--(120:4);
\filldraw circle (1pt) node[below=1ex] {$O$};
\draw[<-, color = blue]  (220:1.2) arc(220:120:1.2) node[midway,left]{$\alpha$};
\draw[latex-latex, color = red]  (220:4) arc(220:120:4) node[midway,left]{L};
\draw[very thick,-latex] (0,0) --  (20:4) node[midway,above]{1};
\draw[very thick,-latex] (0,0) --  (195:4) node[midway,above]{1};
\draw[latex-] (160:4) --++(-2,2) node[pos=1.1] {$B$};
\end{tikzpicture}
\end{document}