*Question E6A05:
How does DC input impedance at the gate of a field-effect transistor (FET) compare with that of a bipolar transistor?*  

*Correct Answer is  C: An FET has higher input impedance*  

### AI Response: (may contain errors)  

In this question, we are comparing the DC input impedance at the gate of a field-effect transistor (FET) with that of a bipolar transistor.

### Explanation:

1. **Correct Answer: C: An FET has higher input impedance**

   - **FETs**: The gate of a field-effect transistor (FET) is insulated from the channel by a thin oxide layer, which means it draws very little current. This results in a very high input impedance, often in the range of megaohms (MΩ) or higher.
   - **Bipolar Transistors**: In contrast, a bipolar junction transistor (BJT) has a base that requires a continuous flow of current to operate, leading to a much lower input impedance, typically in the range of kiloohms (kΩ).

2. **Why the Other Choices are Incorrect:**

   - **Choice A: They are both low impedance**  
     This is incorrect because, as explained, FETs have a high input impedance, while BJTs have a relatively low input impedance.

   - **Choice B: An FET has lower input impedance**  
     This is incorrect because FETs have a higher input impedance compared to BJTs, not lower.

   - **Choice D: They are both high impedance**  
     This is incorrect because only FETs have high input impedance. BJTs have a lower input impedance.

### Useful Rule of Thumb:

- **FETs**: High input impedance due to the insulated gate.
- **BJTs**: Lower input impedance due to the need for base current.

Understanding these characteristics is crucial for designing circuits where input impedance is a key factor.