For silver, we have to calculate (a) the mean free path of conduction electrons and (b) the ratio of mean free path to the distance between neighbouring ions. Silver has a Fermi energy of 5.51 eV and a resistivity of .

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Resistivity of a metal is given in terms of the density of conduction electrons, , the average time of collision of electrons with the lattice, , and the mass of electron, , by the relation

In problem 804 , we have calculated that the number of conduction electrons per cubic meter in silver metal is

.

Therefore, the mean time for collision of a conduction electron with a silver ion at the lattice will be

As conduction electrons will have speed of about , the mean free path for conduction electrons will be

We calculate next the distance between neighbouring ion cores. Let us assume that each ion core is contained inside a cubical lattice of length , the distance between neighbouring ion cores. We thus have the relation

We find

We estimate the ratio of the mean free path to the distance between neighbouring ion cores. It is given by