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jason177
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Homework Statement
Polymers, like rubber, are made of very long molecules, usually tangled up in a configuration that has lots of entropy. As a very crude model of a rubber band, consider a chain of N links, each of length l. Imagine that each link has only two possible states, pointing either left or right. The total length L of the rubber band is the net displacement from the beginning of the first ling to the end of the last link.
Using the thermodynamic identity,express the tension force F in terms of a partial derivative of the entropy. From this expression compute the tension in terms of L,T,N, and l.
Homework Equations
I'm pretty sure the thermodynamic identity for this system is
dU=TdS+fdl
so then solving for f gets
f=dU/dl - TdS/dl
The Attempt at a Solution
so I found an equation for dS/dl but I have no idea how to get dU/dl in terms of L,T,N, and l.