\sect{Tension of a chain molecule I}

% Baruch's  A10

A chain molecule consists of ${N}$ units, each having a
length ${a}$, see figure. The units are joined so as to permit 
free rotation about the joints. At a given temperature ${T}$, derive the
relation between the tension ${f}$ acting between both ends of the
three-dimensional chain molecule and the distance ${L}$ between
the ends. 

\begin{center}
\includegraphics[scale=0.7]{A10}
\end{center}

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