Question

There are very roughly the same number of iron atoms per m³ as there are copper atoms per m³ , but copper is a much better conductor than iron. How does u_iron compare with u_copper?

Short answer

The u_copper is greater than u_iron

Step-by-step solution

Given data

Copper is a better conductor than iron.

Define the concept for the mobility

The mobility in a conductor of cross sectional area A and n number of atoms per unit volume, through which a current i passes on application of electric field E, is defined as follows:

$u=\frac{i}{nAE}$ ..... (i)

Determine the mobility of copper to that of iron

From equation (i) it is evident that for equal number density, area and applied electric field, the conductor which allows more current has better mobility that is the material which is more conducting has larger mobility. Thus, copper has larger mobility that is given as:

$u_{copper}>u_{iron}$