Question

The current amplification of the transformer is $0.8$. The transistor is connected with emitter configuration. Find the change in collector current when the base current changes by $6mA$.
A) $1.2mA$
B) $24mA$
C) $3.6mA$
D) $4.8mA$

Answer 1

Hint: Using the relation between amplification factor and the current gain, find the current gain and current gain is the ratio of collector current and the base current.

Complete step by step answer:
The semiconductor device which is used to amplify or switch electrical signals is called a transistor. Transistor is made up of semiconductor material which has at least three terminals for connection to an external circuit. There are two types of transistors - Bipolar junction transistors and Field effect transformer. The bipolar junction is the type of transistor which consists of three regions and two junctions.
We know that, amplification factor in a transistor is denoted by $\alpha $ and the current gain is denoted by $\beta $.
So, from the question, it is given that –
Amplification factor, $\alpha = 0.8$
Now, by using the relation between current gain and amplification factor –
$\beta = \dfrac{\alpha }{{1 - \alpha }} \cdots \left( 1 \right)$
Putting the value of amplification factor in equation $\left( 1 \right)$, we get –
$
  \beta = \dfrac{{0.8}}{{1 - 0.8}} \\
   \Rightarrow \beta = \dfrac{{0.8}}{{0.2}} \\
   \Rightarrow \beta = 4 \\
 $
Now, we have been given the value of base current in the question and we found the value of current gain so, we can use the relation between current gain, base current and collector current to know the value of collector current. So, for this relation, let the collector current be ${I_c}$ and base current be ${I_b}$. Therefore, -
$
  \beta = \dfrac{{{I_c}}}{{{I_b}}} \\
   \Rightarrow {I_c} = \beta {I_b} \cdots \left( 2 \right) \\
 $
Putting the values of current gain and base current in the equation $\left( 2 \right)$, we get –
$
  {I_c} = 4 \times 6 \\
   \Rightarrow {I_c} = 24mA \\
 $
Hence, the value of collector current is $24mA$.
So, the correct option is (B).

Note: There are following three segments in the transistor:
Emitter – It is the segment of one side of a transistor which has moderate size and is heavily doped to increase current. It supplies the majority of charge carriers.
Base – It is the middle segment of transistor which has thin size and is doped but lightly to reduce recombination.
Collector – It is largest in size and is moderately doped at one end of the transistor. It collects the majority of charge carriers.