使用 Circuitikz 表示等效电阻的箭头和标签

Question

我的电路是黑色的。但我想使用 Circuitikz 添加红色部分（标签和箭头，无论颜色如何）。

以下是我使用的代码：

  \begin{circuitikz}[american, scale = 0.7, transform shape]\shorthandoff{<>}
  \draw 
  (0,0) to[R, l = $R_1$] (0,3)
  to [short] (2,3)
  to [R, l=$R_2$] (2,0)


  (2,3) to[R, l = $R_3$] (5,3)
  to [R, l=$R_4$] (5,0)
  to [short] (0,0)

  (5,3) to[short, -o] (7,3)
  (5,0) to[short, -o] (7,0)

  (7,3.3) node {a}
  (7,-.3) node {b}
  ;
  \end{circuitikz}

Answer 1

尝试（使用 TikZ 来获取带有文字的红色箭头）：

\documentclass[12pt,border=3mm]{standalone}
\usepackage{circuitikz}
\usetikzlibrary{arrows}
%---------------------------------------------------------------%
        \begin{document}
\begin{circuitikz}[american, scale = 0.7, transform shape]
  \draw
  (0,0) to[R, l = $R_1$] (0,3)
  to [short] (2,3)
  to [R, l=$R_2$] (2,0)

  (2,3) to[R, l = $R_3$] (5,3)

  to [R, l=$R_4$] (5,0)
  to [short] (0,0)

  (5,3) to[short, -o] (7,3) node[above]  (a) {a}
  (5,0) to[short, -o] (7,0) node[below]  (b) {b}
  ;
  \draw[>=angle 90,<->,red,% borrowed from TikZ, gives red arrow ...
        shorten <=1mm, shorten >=1mm] (a) to node [fill=white] {RTh} (b);
  \end{circuitikz}
\end{document}