*Question G7B10:
Which of the following describes a linear amplifier?*  

*Correct Answer is  B: An amplifier in which the output preserves the input waveform*  

### AI Response: (may contain errors)  

To understand the concept of a linear amplifier, let's break down the correct answer and the other choices.

### Correct Answer: 
**B: An amplifier in which the output preserves the input waveform**

- **Explanation**: A linear amplifier operates in a way that the output signal is a faithful reproduction of the input signal. This means that the amplifier does not distort the waveform, allowing for high fidelity in audio and other applications. Linear amplifiers are typically used in applications where signal integrity is crucial, such as in audio amplification and certain RF applications.

### Why the Other Choices are Incorrect:

- **A: Any RF power amplifier used in conjunction with an amateur transceiver**
  - **Explanation**: Not all RF power amplifiers are linear. Some may operate in a non-linear mode (like Class C amplifiers) which do not preserve the input waveform. Therefore, this statement is too broad and does not specifically define a linear amplifier.

- **C: A Class C high efficiency amplifier**
  - **Explanation**: Class C amplifiers are designed for high efficiency but are not linear. They operate by conducting for less than half of the input signal cycle, which results in significant distortion of the output waveform. This makes them suitable for applications like RF transmission where efficiency is prioritized over linearity.

- **D: An amplifier used as a frequency multiplier**
  - **Explanation**: Frequency multipliers are typically non-linear devices. They generate output signals at harmonics of the input frequency, which inherently involves distortion of the input waveform. Thus, this choice does not describe a linear amplifier.

### Summary:
- A linear amplifier preserves the input waveform, making it suitable for applications requiring high fidelity.
- Other choices either describe amplifiers that do not maintain linearity or are too general.

### Useful Rule of Thumb:
- **Linear vs. Non-Linear**: If an amplifier is designed to amplify a signal without altering its shape, it is likely a linear amplifier. If it operates in a mode that introduces distortion (like Class C), it is non-linear.