Migration and the Electric Field

In a generalised geometry, the Nernst-Planck equation is given for a species i as 

On the right-hand side, the first term describes diffusion and the second term describes migration. 

By considering the Nernst-Planck equation, discuss the meaning of the concept of electric field . 

The contributions of diffusion and migration are described respectively by the two terms in the right-hand side of the Nernst-Planck equation derived above (Eq. 10.1). 

This law is equivalent to Coulomb s law above, but is written in terms of a charge density rather than in terms of the locations of individual ions, so it is much easier to work with when the number of ions is large. 

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