Plazek and O'Rourke measured the viscosity of polystyrene $(M=3,400)$ as a function of

temperature $($D$.$J$.$ Plazek and V$.$M$.$ O'Rourke, J$.$ Polym. Sci. Part A$-2,9,209,1971).$ Plot

these data in the Arrhenius format versus $\frac{1}{T},$ and find apparent activation energies

for the lowest and highest temperatures measured. Compare these values to those obtained

from the data in Figure $12\mathrm{.}11$b$,$ and comment on their physical significance.