*Question E7H02:
What is a microphonic?*  

*Correct Answer is  C: Changes in oscillator frequency caused by mechanical vibration*  

### AI Response: (may contain errors)  

A microphonic refers to a phenomenon where mechanical vibrations cause changes in the frequency of an oscillator. This is particularly relevant in radio and audio applications where sensitive components can pick up vibrations and inadvertently affect their performance.

### Explanation of the Correct Answer:
- **Correct Answer: C: Changes in oscillator frequency caused by mechanical vibration**  
  - This is correct because microphonics occur when vibrations (like those from sound waves or physical movement) affect the components of an oscillator, leading to variations in its frequency. This can result in unwanted noise or distortion in the output signal.

### Explanation of Incorrect Answers:
- **A: An IC used for amplifying microphone signals**  
  - This is incorrect because a microphonic is not an integrated circuit (IC) but rather a phenomenon related to frequency changes due to vibrations.

- **B: Distortion caused by RF pickup on the microphone cable**  
  - This is incorrect because while RF pickup can cause distortion, it is not specifically related to the mechanical vibrations that define microphonics. RF pickup is more about interference rather than frequency changes due to physical movement.

- **D: Excess loading of the microphone by an oscillator**  
  - This is incorrect because excess loading refers to the impedance mismatch or overloading of a microphone circuit, which does not relate to the mechanical vibrations affecting frequency.

### Summary:
Microphonics are significant in radio and audio systems as they can introduce noise and affect signal integrity. Understanding this concept helps in troubleshooting and designing circuits that minimize such effects.