(15) If a rubber band is stretched, the reversible work is given by W=Fdl, where F is the tension on the band and l is the length. Assume no pdV term. (a) Write down the differential form of thermodynamic potential , which is a function of T and . (Hint: You may want to describe the internal energy, U, of the given system first.) (b) Find the Maxwell relation for (lS)T