A) \[\frac{25}{24}\]
B) \[\frac{24}{25}\]
C) \[\frac{25}{26}\]
D) \[\frac{26}{25}\]
Correct Answer: B
Solution :
Key Idea: Emitter current is sum of base current and collector current. The current gain \[(\alpha )\] for a transistor is given by \[\alpha =\frac{\Delta {{I}_{C}}}{\Delta {{I}_{E}}}\] ... (i) Also\[,\] \[\Delta {{I}_{E}}=\Delta {{I}_{C}}+\Delta {{I}_{B}}\] ?. (ii) From Eqs. (i) and (ii), we get \[\alpha =\frac{\Delta {{I}_{E}}-\Delta {{I}_{B}}}{\Delta {{I}_{E}}}\] Given,\[\Delta {{I}_{E}}=25\,\,mA,\,\,\Delta {{I}_{B}}=1\,\,mA\] \[\therefore \] \[\alpha =\frac{25-1}{25}=\frac{24}{25}\] Note: Current gain \[(\alpha )\] is usually less than one, hence, options and cannot be correct.
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