Final answer:
In a common base connection, if the current amplification factor is 0.9 and the emitter current is 1mA, the base current can be calculated by subtracting the collector current from the emitter current.
Step-by-step explanation:
In a common base connection, the current amplification factor (beta) is defined as the ratio of the collector current to the emitter current. In this case, the current amplification factor is given as 0.9, which means for every 1mA of emitter current, the collector current will be 0.9mA.
To find the base current, we can use the formula:
beta = collector current / emitter current
0.9 = collector current / 1mA
From this equation, we can solve for the collector current:
collector current = 0.9 * 1mA = 0.9mA
Therefore, the base current is equal to the emitter current minus the collector current:
base current = emitter current - collector current = 1mA - 0.9mA = 0.1mA