*Question G7A05:
What portion of the AC cycle is converted to DC by a half-wave rectifier?*  

*Correct Answer is  B: 180 degrees*  

### AI Response: (may contain errors)  

In a half-wave rectifier, only one half of the AC cycle is used to produce DC. Let's break down the question:

1. **Correct Answer Explanation (180 degrees)**:
   - A full AC cycle is 360 degrees, which represents one complete waveform (positive and negative halves).
   - A half-wave rectifier only allows the positive half of the AC waveform to pass through, effectively blocking the negative half.
   - Therefore, the portion of the AC cycle that is converted to DC is 180 degrees (the positive half).

2. **Why the Other Choices are Incorrect**:
   - **A: 90 degrees**: This would imply that only a quarter of the cycle is used, which is not the case for a half-wave rectifier.
   - **C: 270 degrees**: This would suggest that three-quarters of the cycle is converted to DC, which is incorrect as it still only uses the positive half.
   - **D: 360 degrees**: This would mean the entire cycle is converted to DC, which is not true for a half-wave rectifier since it does not utilize the negative half.

3. **Useful Formulas or Rules of Thumb**:
   - Remember that a half-wave rectifier only utilizes the positive half of the AC waveform, which corresponds to 180 degrees of the 360-degree cycle.
   - The average output voltage ($V_{avg}$) of a half-wave rectifier can be calculated using the formula:
   $$V_{avg} = \frac{V_{m}}{\pi}$$
   where $V_{m}$ is the peak voltage of the AC input.

This understanding is crucial for grasping how half-wave rectification works and its implications in practical applications.