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248 CHAPTER 3

Fig. 3.16. The variation in the thickness of the ionic
cloud as a function of electrolyte concentration (1 Å = 0.1
nm).

Then let the charge on the cloud be switched on. The potential at the distance
r from the central ion is no longer given by the central ion only. It is given by the law
of superposition of potentials (Fig. 3.17); i.e., is the sum of the potential due to the
central ion and that due to the ionic cloud