*Question G4E09:
What is the approximate open-circuit voltage from a fully illuminated silicon photovoltaic cell?*  

*Correct Answer is  B: 0.5 VDC*  

### AI Response: (may contain errors)  

A silicon photovoltaic cell, when fully illuminated, generates an open-circuit voltage due to the photovoltaic effect. This is the voltage measured across the cell's terminals when no current is flowing.

1. **Correct Answer: 0.5 VDC (Choice B)**
   - The typical open-circuit voltage for a single silicon photovoltaic cell is approximately 0.5 volts. This is a characteristic of the material and the way it converts light into electrical energy.

2. **Why the Other Choices are Incorrect:**
   - **Choice A: 0.02 VDC**  
     - This voltage is too low for a silicon photovoltaic cell. Such a low voltage would not be practical for generating usable power.
   - **Choice C: 0.2 VDC**  
     - While closer than Choice A, 0.2 VDC is still below the typical range for a silicon cell. It does not reflect the typical open-circuit voltage.
   - **Choice D: 1.38 VDC**  
     - This voltage is too high for a single silicon photovoltaic cell. It exceeds the typical range and would not be expected from a single cell.

3. **Useful Rule of Thumb:**
   - A single silicon photovoltaic cell typically produces an open-circuit voltage of about 0.5 VDC when fully illuminated. This is a standard value used in designing and understanding solar power systems.

Understanding these characteristics helps in designing and troubleshooting solar power systems, as well as in selecting the correct components for a given application.