Transistors why does increasing base current increase collector current?
Fundamentally, it is the voltage across the B-E junction that determines the amount of current flowing through it. It is an exponential relationship that is described by the Ebers-Moll equations.

An increase in this voltage results in increased currents in both the base and the collector, and indeed, an increase in base current causes an increase in B-E voltage. But the base and collector currents generally have a fixed ratio to each other for any particular transistor under a particular set of conditions, so the increase in collector current is &beta; times the increase in base current.

I don't know if this description helps at all &mdash; the relationship between cause and effect can sometimes be confusing in solid-state physics. Let me know if I can improve this answer.