You are tasked with solving that exercise, analytically step-by-step. Show your work, explain the methodologies used. Use \boxed{} for the final result. Format them for LaTeX.

Make any neccessary diagrams using tikz or pgfplots in the same code box as the solution and include, make them in a figure environment and use \centering.

Make sure the solution is accurate, smart, easy to follow and solve the problem the fastest and easiest way possible, while giving an accurate result. The highest level math that you can use to solve the exercises are 1st year physics undergrad math.

If you don't have enough data for a problem (e.g. you need a circuit diagram) say that you cannot solve that particular exercise with the available data and move on to the next.

Do not use \textbf{}, ** **, or \section \subsection \subsubsection commands just say for example: Βήμα: with no additional commands. Please write in Greek, use correct terminology. If you want to itemize/enumerate stuff use the appropriate LaTeX commands: \begin{itemize} or \begin{enumerate}[(i)]. Do not use \textbf{} anywhere in the code. Make sure the LaTeX code is formatted appropriately and compiles with no errors. Write the complete answer inside a single code box. Include only the code for the problem, not the whole document.

Be extra careful when making figures with tikz and pgfplots, make sure the code is correct and they compile without errors.

Here is the problem:

Μια ράβδος μήκους $L$ βρίσκεται στον άξονα $x$ με το αριστερό της άκρο στην αρχή των αξόνων. Έχει ανομοιόμορφη πυκνότητα φορτίου $\lambda = ax$, όπου το $a$ είναι μια θετική σταθερά.
\begin{enumerate}
    \item Ποιες είναι οι μονάδες του $a$;
    \item Υπολογίστε το ηλεκτρικό δυναμικό στο σημείο $A$.
\end{enumerate}
\FloatBarrier
\begin{figure}[!ht]
\centering
\resizebox{0.5\textwidth}{!}{%
\begin{circuitikz}
\tikzstyle{every node}=[font=\LARGE]
% Vertical line (y-axis)
\draw [line width=1pt] (6.25,14.25) -- (6.25,5.5);

% Horizontal line (x-axis)
\draw [line width=1pt] (1.25,6.75) -- (13.75,6.75);

% Rectangle with color and slight border thickness for clarity
\draw [fill={rgb,255:red,203; green,200; blue,200}, draw=black, line width=1pt] (6.25,7) rectangle (12.5,6.5);

% Arrows for force L
\draw [line width=1.2pt, ->, >=Stealth] (9.25,6) -- (6.25,6);
\draw [line width=1.2pt, ->, >=Stealth] (10.25,6) -- (12.5,6);

% Labels
\node [font=\LARGE] at (9.75,6) {L};
\node [font=\LARGE] at (6.75,14.25) {y};
\node [font=\LARGE] at (14.25,6.75) {x};
\node [font=\LARGE] at (4.75,8.25) {d};
\node [font=\LARGE] at (2,6) {A};
\node [font=\LARGE] at (11.25,11) {b};
\node [font=\LARGE] at (9.75,14) {B};

% A's position
\draw [line width=1.2pt] (2.5,6.75) -- (2.5,7.75);
\draw [line width=1.2pt, <->, >=Stealth] (2.5,7.5) -- (6.25,7.5);
\node at (2.5,6.75) [circ] {};

% B's position and dashed line
\draw [line width=1.2pt] (12.5,6.5) -- (12.5,5.75);
\draw [line width=1.2pt, dashed] (10.25,14.25) -- (10.25,7);
\draw [line width=1.2pt, ->, >=Stealth] (11.25,10.5) -- (11.25,7.25);
\draw [line width=1.2pt, ->, >=Stealth] (11.25,11.75) -- (11.25,14.25);
\draw [line width=1.2pt] (11.25,14.25) -- (10.25,14.25);
\draw [line width=1.2pt, dashed] (10.25,15.25) -- (10.25,14);
\node at (10.25,14.25) [circ] {};

\end{circuitikz}
}%
\label{fig:my_label}
\end{figure}
\FloatBarrier