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mobility (u)

Mobility (u) :

The conductivity of a substance is due to its mobile charge carrier ( electrons in case of metals,  +ve and -ve ions in case of electrolyte and electron & holes in case of semiconductors)

 mobilty of the charge carrier is defined as the magnitude of Drift velocity per unite electric field. 
 
 u= vd/E
where vd is drift velocity and E is electric field 

In case of conductor or metals sigma =( ne)×e×(nh)


In case of semiconductor sigma =( ne) ×e× (ue) +( nh) ×e×( nh) 


where (ne)  , e  & (nh)  are number of electrons per unit volume ,  electric charge & electron mobility respectively. 
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