define mobility of a charge carrir.how does eletric current depend on it

This is a property of conductor, defined as the ratio of drift velocity to applied electric field in a conductor. Drift velocity of charge carriers in a conductor depend upon two factors, one is the intensity of applied electric field across the conductor and other is one property of the conductor called Mobility of Charge Carrier. In other words, for applied same electric field, on different metallic conductors there will be different drift velocities of electrons. These drift velocities of electrons depend upon a typical property of conductor called mobility of charge carrier