258 Chapter 7. Entropic forces at work[[Student version, January 17, 2003]]
7.10 T 2 Charged surfaces
Use some numerical software to solve Equation 7.29 forβas a function of plate separation 2Dfor
fixed charge densityσq.For concreteness takeσqto equale/(20nm^2 ). Now convert your answer
into a force using Equation 7.31 and compare to Figure 7.11. Repeat with other values ofσqto find
(roughly) which one best fits the upper curve in the figure at separation greater than 2nm.Ifthis
surface were fully dissociated, it would have one electron charge per 7nm^2 .Isitfully dissociated?
7.11 T 2 Direct calculation of a surface force
Finish the derivation of Section 7.4.4′on page 251. The goal is to establish Equation 7.31.