Answer:
Ib = 0.1 mA
Explanation:
You want the base current in a common-base circuit that has an emitter current of 1 mA and an amplification factor of 0.9.
The amplification factor (gain) is the ratio of collector current to emitter current. The emitter current is the sum of the collector current and the base current. Thus, we have two equations that let us solve for the base current:
Ib +Ic = Ie
Ic/Ie = gain
Solving the second equation for Ic gives ...
Ic = Ie·gain
Substituting into the first equation, we have ...
Ib +Ib·gain = Ie
And solving for Ib gives ...
Ib = Ie(1 -gain) = (1 mA)(1 - 0.9) = 0.1 mA
The value of the base current is 0.1 mA.
