The current gain for a transistor working as a common-base amplifier is `0.96`. If the emitter current is `7.2 mA`, the base current will be

Options

A. `0.29 mA`
B. `0.35 mA`
C. `0.39 mA`
D. `0.43 mA`

Answer

To find the base current (IB) for a transistor working as a common-base amplifier, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Current Gain (α)**:
The current gain for a common-base amplifier is given as α = 0.96. This means that the ratio of the collector current (IC) to the emitter current (IE) is 0.96.

2. **Given Values**:
- Emitter current (IE) = 7.2 mA
- Current gain (α) = 0.96

3. **Calculate the Collector Current (IC)**:
We can use the formula:
\[ IC = α \times IE \]
Substituting the known values:
\[ IC = 0.96 \times 7.2 \, \text{mA} \]
\[ IC = 6.912 \, \text{mA} \approx 6.91 \, \text{mA} \]

4. **Use the Relationship Between Currents**:
The relationship between the emitter current (IE), collector current (IC), and base current (IB) is given by:
\[ IE = IC + IB \]
Rearranging the equation to find the base current (IB):
\[ IB = IE - IC \]

5. **Substitute the Values**:
Now substitute the values of IE and IC:
\[ IB = 7.2 \, \text{mA} - 6.91 \, \text{mA} \]
\[ IB = 0.29 \, \text{mA} \]

6. **Final Answer**:
Therefore, the base current (IB) is:
\[ IB = 0.29 \, \text{mA} \]

### Summary:
The base current for the transistor working as a common-base amplifier is **0.29 mA**.