Question

When the base current in a transistor is changed from 30µA to 80µA, the collector current is changed from 1.0 mA to 3.5 mA. Find the current gain β.

Answer 1

Given:
Change in the base current, $\delta I_{\mathrm{b}}=(80-30)\mathrm{\mu A}$
Change in the collector current, $\delta I_c=(3.5-1)\mathrm{mA}$
Base current gain = Rate of change of collector current with respect to base current
Thus,
$$\begin{gathered} \beta =\left(\frac{\delta l_{\mathrm{c}}}{\delta l_{\mathrm{b}}}\right)\mathrm{at}\mathrm{constant}{V}_{\mathrm{cc}} \\ \Rightarrow \beta =\frac{2.5\times {10}^{-3}}{50\times {10}^{-6}} \\ \Rightarrow \beta =\frac{250}{50}=50 \end{gathered}$$
∴ Current gain = 50