Question

In a common emitter amplifier an increase of 50 A in base current causes a 1.0 mA increase in collector current. Calculate current gain β. What will be the change in emitter current ? Calculate α with the help of β.

Answer 1

Change in base current ΔI_E = 50 µA
Change in collector current ΔI_C = 1.0 mA
\(\therefore \beta=\frac{\Delta I_{C}}{\Delta I_{B}}=\frac{1.0 {mA}}{50 \mu {A}}=\frac{1 \times 10^{-3}}{50 \times 10^{-6}}=\frac{1000}{50}=20\)
So, the change in emitter current
ΔI_E = ΔI_B + ΔI_C
= 50 µA + 1.0 mA
= 50 µA + 1000 µA = 1050 µA = 1.050 mA
Now, α = \(\frac{\beta}{1+\beta}=\frac{20}{20+1}=\frac{20}{21}\) = 0.9523
α = 0.95