*Question T5C05:
What is the unit of impedance?*  

*Correct Answer is  D: The ohm*  

### AI Response: (may contain errors)  

The correct answer to the question about the unit of impedance is **D: The ohm**.

### Explanation of the Correct Answer:
- **Impedance** is a measure of how much a circuit resists the flow of alternating current (AC). It combines both resistance (the opposition to current flow) and reactance (the opposition due to capacitance and inductance).
- The unit of impedance is the **ohm**, which is represented by the symbol $\Omega$. 

### Why the Other Choices are Incorrect:
- **A: The volt**  
  - The volt is the unit of electric potential or electromotive force, not impedance. It measures the potential difference that drives current through a circuit.

- **B: The ampere**  
  - The ampere is the unit of electric current. It measures the flow of electric charge, not the opposition to that flow.

- **C: The coulomb**  
  - The coulomb is the unit of electric charge. It quantifies the amount of electric charge, not the resistance or opposition to current flow.

### Useful Formulas:
- Impedance ($Z$) in an AC circuit can be expressed as:
  $$Z = R + jX$$
  where:
  - $R$ = resistance (in ohms)
  - $X$ = reactance (in ohms)
  - $j$ = the imaginary unit (used to represent the phase difference between voltage and current)

This formula shows how impedance is a combination of resistance and reactance, both measured in ohms. Understanding this concept is crucial for working with AC circuits in amateur radio and other applications.