drop of tension at transistor base

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I would like to know, how do we calcul the drop of tension a the transistor base (in common collector circuit) example if I inject 10V in a resistor of 100 Ohm, why at the base the voltage is going to be around 8V ??? is it because of the base resistor (Rin)?
please help me, I'm a bit mixte up!!
thanks a lot

 

[lladnar23]

First, we know that there is going to be some base current through the transistor, right? Well, that current must flow through your 100 ohm resistor, producing a voltage drop equal to Ib * R, where Ib is the base current. If you see a 2V drop across that resistor, you know that your base current is 20mA.