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  • The current gain  of a transistor is <img alt="\mathrm{0.9.}" src="https://entran

The current gain \mathrm{\alpha } of a transistor is \mathrm{0.9.} The transistor is connected to common base configuration. What would be the change in collector current when base current changes by \mathrm{4\ mA}?

Option: 1

\mathrm{1.2\ mA}


Option: 2

\mathrm{12\ mA}


Option: 3

\mathrm{24\ mA}


Option: 4

\mathrm{36\ mA}


Answers (1)

best_answer

The ratio of collector current \mathrm{(I_{c})} to emitter current \mathrm{(I_{e})} is known as current gain \mathrm{(\alpha )} of a transistor. Therefore,
\mathrm{\alpha =\frac{\Delta I_{c}}{\Delta I_{e}}\ \ \ ...............(i)}
Also, emitter current is equal to sum of change of base current and collector current.
Therefore,
\mathrm{\Delta I_e=\Delta I_b+\Delta I_c\ \ \ \ ............(ii)}
From Eqs. \mathrm{(i)} and \mathrm{(ii)}, we get
\mathrm{\alpha=\frac{I_c}{\Delta I_b+\Delta I_c}} \\\\ \mathrm{Given,\ \alpha=0.9, \Delta I_b=4 \mathrm{~mA}}
\begin{aligned} &\mathrm{ 0.9=\frac{I_c}{4+\Delta I_c} }\\ &\mathrm{ \Rightarrow \quad 0.9\left(4+I_c\right)=I_c} \\ &\mathrm{ \Rightarrow \quad 3.6+0.9 I_c=I_c }\\ &\mathrm{ \Rightarrow \quad 3.6=0.1 I_c }\\ &\mathrm{ \Rightarrow \quad I_c=36 \mathrm{~mA}} \end{aligned}

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shivangi.bhatnagar

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