For a transistor in CB configuration, the collector current is 4.5mA and base current is 45uA.
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For a transistor in CB configuration, the collector current is 4.5mA and base current is 45uA. Calculate the value of current amplification factor.
Show answer & explanation
The current amplification factor alpha (α) in a common-base configuration is defined as the ratio of collector current to emitter current: α = Ic / Ie. Since Ie = Ic + Ib, we have α = Ic / (Ic + Ib) = 4.5 mA / (4.5 mA + 0.045 mA) = 4.5 / 4.545 ≈ 0.99. Alpha is always less than 1 because some base current is required to sustain the collector current.
Step-by-step Derivation:
Given:
- Collector current (Ic) = 4.5 mA
- Base current (Ib) = 45 µA = 0.045 mA
Step 1: Calculate emitter current
Ie = Ic + Ib = 4.5 + 0.045 = 4.545 mA
Step 2: Calculate alpha (current amplification factor in CB configuration)
α = Ic / Ie
α = 4.5 / 4.545
α = 0.9901...
α ≈ 0.99
Note: Alpha always ranges between 0 and 1. The relationship between α and β (common-emitter current gain) is: β = α / (1 - α) = 0.99 / 0.01 = 99, which is a reasonable value.