*Question G5A08:
What is impedance?*  

*Correct Answer is  C: The ratio of voltage to current*  

### AI Response: (may contain errors)  

Impedance is a fundamental concept in electrical engineering and radio communications. It is defined as the ratio of voltage to current in an AC circuit.

### Correct Answer: C - The ratio of voltage to current

- **Explanation**: Impedance ($Z$) is represented mathematically as:
  
  $$Z = \frac{V}{I}$$

  where:
  - $V$ = voltage (in volts)
  - $I$ = current (in amperes)

  Impedance combines both resistance (real part) and reactance (imaginary part) in AC circuits, making it a complex quantity.

### Why the Other Choices are Incorrect:

- **A: The ratio of current to voltage**  
  - This is incorrect because it describes the reciprocal of impedance, known as admittance ($Y$):
  
  $$Y = \frac{I}{V}$$

- **B: The product of current and voltage**  
  - This is incorrect because the product of current and voltage gives power ($P$), not impedance:
  
  $$P = V \times I$$

- **D: The product of current and reactance**  
  - This is incorrect because it does not define impedance. Instead, the product of current ($I$) and reactance ($X$) gives the reactive power ($Q$):
  
  $$Q = I \times X$$

### Summary

- Impedance is the ratio of voltage to current in an AC circuit, represented as $Z = \frac{V}{I}$.
- Understanding impedance is crucial for analyzing AC circuits, especially in radio frequency applications.