Common-Base Configuration and Current Gain

The common-base configuration is a type of transistor amplifier circuit where the base terminal of the transistor is a common terminal for both input and output signals. It is characterized by a low input impedance and a high output impedance.

In this configuration, the current gain, also known as the current transfer ratio (hfe), is defined as the ratio of the change in the collector current (ΔIC) to the change in the emitter current (ΔIE), assuming all other parameters remain constant.

Given Data:
- IE = 4.2 mA
- IC = 4.0 mA
- Current gain (hfe) = ?

Calculating the Current Gain:
To calculate the current gain, we can use the basic formula:

hfe = ΔIC / ΔIE

In this case, since we have the values of IE and IC, we can assume that the change in these currents is negligible, and therefore ΔIC ≈ IC and ΔIE ≈ IE.

So, the current gain can be calculated as:

hfe = IC / IE

Substituting the given values:

hfe = 4.0 mA / 4.2 mA

Simplifying the expression:

hfe = 0.952

Interpreting the Result:
The calculated value of the current gain is 0.952. However, the correct answer is mentioned as between 0.95 and 0.96. This suggests that the actual value lies within this range and is rounded to two decimal places.

Since the given values of IE and IC are rounded to one decimal place (4.2 mA and 4.0 mA), it is reasonable to assume that the desired answer is also rounded to two decimal places.

Therefore, the correct current gain for the common-base configuration with the given values is between 0.95 and 0.96.