*Question E6C02:
What happens when the level of a comparator’s input signal crosses the threshold voltage?*  

*Correct Answer is  B: The comparator changes its output state*  

### AI Response: (may contain errors)  

When the level of a comparator’s input signal crosses the threshold voltage, the correct answer is:

**B: The comparator changes its output state.**

### Explanation of the Correct Answer:
- A comparator is a device that compares two input voltages and outputs a digital signal indicating which input is higher.
- When the input signal exceeds the threshold voltage (the reference level), the comparator switches its output from one state to another (typically from low to high or vice versa).
- This behavior is fundamental to how comparators function in circuits, making this answer correct.

### Why the Other Choices are Incorrect:
- **A: The IC input can be damaged**
  - While excessive input voltage can damage a comparator, crossing the threshold voltage itself does not cause damage. Comparators are designed to handle input signals within specified limits.
  
- **C: The reference level appears at the output**
  - The output of a comparator does not simply reflect the reference level. Instead, it indicates whether the input is above or below the reference level, resulting in a binary output (high or low).
  
- **D: The feedback loop becomes unstable**
  - This statement is not applicable to the basic operation of a comparator. Feedback loops can be part of more complex circuits (like oscillators), but a simple comparator does not inherently involve feedback that would become unstable when the input crosses the threshold.

### Summary:
- A comparator's primary function is to change its output state based on the comparison of input signals against a threshold voltage. Understanding this behavior is crucial for using comparators effectively in various applications.