Scaling components in CircuiTikz

I would like to know how to scale a single component in CircuiTikZ.

There are several possibilities to scale paths, a hole diagram, etc., but I didn't find a way to do so with a single component.

Note: I'm trying to scale a voltage source.

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I don't see an official way to do it, but it appears that all the lengths are based on /tikz/circuitikz/bipoles/length, so you can just change that. Here is the default size and scaled version in between:

\documentclass[border=5pt]{standalone}
\usepackage{tikz}
\usepackage{circuitikz}
\usepackage{siunitx}

\begin{document}
\begin{circuitikz}
\draw (0,0)
to [sV=$a_1$] (2,0)
to [C=$\SI{100}{\ohm}$](3,0)
to [/tikz/circuitikz/bipoles/length=2.5cm,sV=$a_2$] (5,0)
to [sV=$a_1$] (7,0);
\end{circuitikz}
\end{document}​

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I've tried this before and it works, but I was searching something like the 'scale' command. In the absence of a better solution I take this as the correct answer. For further uses it could be complemented with a '\newcommand'. –  Leonardo Dec 19 '11 at 10:55