*Question E7B12:
What type of amplifier circuit is shown in Figure E7-1?*  

*Correct Answer is  C: Common emitter*  

### AI Response: (may contain errors)  

To determine the type of amplifier circuit shown in Figure E7-1, we need to understand the characteristics of each amplifier configuration.

### Correct Answer: Common Emitter

1. **Why the correct answer is correct:**
   - A common emitter amplifier configuration has the input signal applied between the base and the emitter, while the output is taken from the collector. This configuration provides significant voltage gain and is widely used in amplifying applications. 
   - In a common emitter setup, the output is inverted relative to the input, which is a key characteristic of this type of amplifier.

### Why the other choices are incorrect:

2. **Common Base (Choice A):**
   - In a common base configuration, the input is applied to the emitter and the output is taken from the collector. This configuration is less common for voltage amplification and is typically used for high-frequency applications. It does not provide voltage gain like the common emitter.

3. **Common Collector (Choice B):**
   - The common collector configuration, also known as an emitter follower, has the input applied to the base and the output taken from the emitter. This configuration provides current gain but no voltage gain, and the output follows the input voltage closely.

4. **Emitter Follower (Choice D):**
   - The emitter follower is another name for the common collector configuration. It is characterized by a high input impedance and low output impedance, making it suitable for impedance matching rather than voltage amplification.

### Useful Formulas and Rules of Thumb:

- **Voltage Gain ($A_V$) for Common Emitter:**
  $$A_V \approx -\frac{R_C}{R_E}$$
  where:
  - $R_C$ = collector resistor
  - $R_E$ = emitter resistor (if unbypassed)

- **Input and Output Impedance:**
  - Common emitter amplifiers typically have moderate input impedance and high output impedance, making them suitable for many applications.

Understanding these configurations and their characteristics will help you identify amplifier types in exam questions effectively.