Question

The current gain in the transistor in common base mode is 0.99. To change the emitter current by 5 mA, the necessary change in collector will be
A. 0.196 mA
B. 2.45 mA
C. 4.95 mA
D. 5.1 mA

Answer 1

A semiconductor device used to amplify (positive and negative both) the electronics signals is known as the Transistors. It is a three-terminal device with the emitter, base, and collector terminals. Basically, it is of two types, i.e., NPN-transistor and PNP-transistors.
In this question, we need to calculate the change in the collector current while it is given that the change in the emitter current should be 5 mA with the current gain of 0.99 in the common base mode.

Complete step by step answer:
The current gain of the transistor is 0.99, and the change in the emitter current is 5 mA.

Current gain is the ratio of the change in the collector current to the change in the emitter current in a transistor. Mathematically $\alpha = \dfrac{{\vartriangle {I_c}}}{{\vartriangle {I_e}}}$.

Now, substitute the value of the change in the emitter current as 5 mA and 0.99 as the current gain in the formula $\alpha = \dfrac{{\vartriangle {I_c}}}{{\vartriangle {I_e}}}$ to determine the change in the collector current in the transistor.

$\alpha = \dfrac{{\vartriangle {I_c}}}{{\vartriangle {I_e}}} \\\ 0.99 = \dfrac{{\vartriangle {I_c}}}{{5{\text{ mA}}}} - - - - (i) \\\$

Cross multiplying the terms in equation (i) as:

$\vartriangle {I_c} = 0.99 \times 5{\text{ mA}} \\\ = 4.95{\text{ mA}} \\\$

Hence, the necessary change in the collector current to change the emitter current by 5 mA with the current gain in the transistor in common base mode is 0.99 is 4.95 mA.

So, the correct answer is “Option C”.

Note:
Students should ensure to use the change in the collector and the emitter current and not the total or instantaneous currents in the formula of the current gain.we need to use the formula for the current gain, which is the ratio of the change in the collector current to the change in the emitter current.