Font size not changing for figures

Code:

\documentclass[12pt]{article}\usepackage{float}\usepackage[american,siunitx]{circuitikz}\begin{document}     \noindent    Hello\newline    \footnotesize    This is small.    \begin{figure}[H]        \centering        \begin{circuitikz}            \draw(0, 0) to [V, v_= $v_g\left(t\right)$] ++(0, -3) ;            \draw(0, 0) to [R, l^= $R$] ++(3,0) to [C, l^=$C$] ++(0, -3) -- ++(-3,0);        \end{circuitikz}        \caption{A simple low-pass filter.}        \label{RCFilter}    \end{figure}    \noindent    This is small.\end{document}

Output:

I realized that when I used the \footnotesize command, the text changes, but the figure captions do not. Is there a way of getting the font of the figure's text to be changed, the same effect as if I change \documentclass[12pt]{article} to \documentclass[10pt]{article}?

Note: I am not sure if this is true, but I think that under my situation, the section headers' fonts may remain unchanged besides the text in the figures.