Question

-In a p-n-p transistor, working as a common base amplifier, current gain is 0.96 and emitter current is 7.2 mA. The base current is
A. 0.20 mA
B. 0.36 mA
C. 0.29 mA
D. 0.45 mA

Answer 1

Hint: This is a problem based on the p-n-p transistor .In common base amplifiers the collector current is the sum of the base and emitter current. The common-base amplifier has Input between emitter and base and output between collector and base. First we will find the collector current by the given current gain because emitter current is given then for finding the base current we will use the collector current expression.

Complete step by step answer:There is given in the question that the current gain \[\beta = 0.96\] and emitter current ${I_E} = 7.2\;mA$
We know that the current gain in common base configuration is the ratio collector current to the emitter current .
So, $\beta = \dfrac{{{I_C}}}{{{I_E}}}$
Where, ${I_C}$ is used to denote the collector current and ${I_E}$ is used to denote the emitter current.
From the above expression we can calculate the Collector current ${I_c}$ that is shown below.
$
0.96 = \dfrac{{{I_C}}}{{7.2}}\\
\implies {I_C} = 6.912\;mA
$
Hence, the collector current is calculated, now by the use of this collector current we will calculate the base current.
For a common base amplifier the collector current is equal to the sum of base current and emitter current, so ${I_C} = {I_E} + {I_B}$
Putting the values of ${I_c}$ and ${I_E}$ we can easily find out the base current as shown below
$
6.912 = 7.2 + {I_B}\\
\implies {I_B} \approx 0.29\;mA
$

Therefore, the base current is 0.29mA. Hence from the given options, only option (C) is correct.

Note:
The collector current is highly dependent on the configuration of the transistor and when the configuration changes the expression for collector current changes accordingly so we must notice the configuration while solving the problems of the transistor.