*Question G0A02:
Which of the following is used to determine RF exposure from a transmitted signal?*  

*Correct Answer is  D: All these choices are correct*  

### AI Response: (may contain errors)  

To determine RF exposure from a transmitted signal, you need to consider several factors that contribute to the overall exposure level. The correct answer is "All these choices are correct" because each factor plays a role in assessing RF exposure:

1. **Duty Cycle**:  
   - The duty cycle is the fraction of time a transmitter is actively transmitting. A higher duty cycle means more continuous exposure, increasing the potential RF exposure.
   - Formula:  
     $$\text{Duty Cycle} = \frac{\text{Time Transmitting}}{\text{Total Time}}$$

2. **Frequency**:  
   - Different frequencies have different penetration abilities and biological effects. RF exposure limits vary with frequency because the human body absorbs RF energy differently at different frequencies.

3. **Power Density**:  
   - Power density is the amount of power per unit area, typically measured in watts per square meter ($\text{W/m}^2$). It directly relates to the intensity of the RF field and is a critical factor in determining exposure levels.
   - Formula:  
     $$\text{Power Density} = \frac{\text{Power Output}}{\text{Area}}$$

Each of these factors contributes to the overall assessment of RF exposure, which is why the correct answer is that all these choices are correct. None of the individual factors alone can provide a complete picture of RF exposure.