*Question G4B05:
Why do voltmeters have high input impedance?*  

*Correct Answer is  D: It decreases the loading on circuits being measured*  

### AI Response: (may contain errors)  

Voltmeters are designed with high input impedance to minimize their impact on the circuit being measured. Here's why the correct answer is correct and why the other choices are incorrect:

1. **Correct Answer: D - It decreases the loading on circuits being measured**
   - **Explanation**: When a voltmeter is connected across a component in a circuit, it forms a parallel path. If the voltmeter has low input impedance, it will draw significant current, altering the circuit's operation and affecting the voltage reading. High input impedance ensures that the voltmeter draws minimal current, thus reducing its impact on the circuit and providing an accurate measurement.

2. **Incorrect Choices**:
   - **A: It improves the frequency response**
     - **Explanation**: Frequency response is more related to the bandwidth and the ability of the voltmeter to accurately measure AC signals at different frequencies. High input impedance primarily affects loading, not frequency response.
   - **B: It allows for higher voltages to be safely measured**
     - **Explanation**: The ability to measure higher voltages safely is more about the voltmeter's voltage rating and insulation, not its input impedance. High input impedance is about minimizing circuit loading.
   - **C: It improves the resolution of the readings**
     - **Explanation**: Resolution is determined by the voltmeter's display and internal analog-to-digital converter, not by its input impedance. High input impedance ensures accurate readings by minimizing circuit loading, but it doesn't directly affect resolution.

**Rule of Thumb**: Always use a voltmeter with an input impedance at least 10 times greater than the impedance of the circuit being measured to minimize loading effects.