The current gain for a common emitter amplifier is 69. If the emitter current is 7 mA, the base current is

Options

A. 0.1 mA
B. 1 mA
C. 0.2 mA
D. 2 mA

Explanation

To find the base current (IB) in a common emitter amplifier given the current gain (β) and the emitter current (IE), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Given Values**:
- Current gain (β) = 69
- Emitter current (IE) = 7 mA

2. **Understand the Relationship Between Currents**:
- In a common emitter amplifier, the relationship between the emitter current (IE), collector current (IC), and base current (IB) can be expressed as:
\[ IE = IC + IB \]
- However, for a common emitter configuration, the collector current (IC) can be approximated as:
\[ IC \approx IE \]
- Thus, we can say:
\[ IC = IE = 7 \text{ mA} \]

3. **Use the Current Gain Formula**:
- The current gain (β) is defined as:
\[ β = \frac{IC}{IB} \]
- Rearranging this formula gives us the base current:
\[ IB = \frac{IC}{β} \]

4. **Substitute the Known Values**:
- Substitute the values of IC and β into the equation:
\[ IB = \frac{7 \text{ mA}}{69} \]

5. **Calculate the Base Current**:
- Performing the division:
\[ IB \approx 0.1014 \text{ mA} \approx 0.1 \text{ mA} \]

### Final Answer:
The base current (IB) is approximately **0.1 mA**.

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