*Question E9F03:
Why is the electrical length of a coaxial cable longer than its physical length?*  

*Correct Answer is  D: Electromagnetic waves move more slowly in a coaxial cable than in air*  

### AI Response: (may contain errors)  

The correct answer to the question about the electrical length of a coaxial cable is:

**D: Electromagnetic waves move more slowly in a coaxial cable than in air.**

### Explanation of the Correct Answer:
- **Speed of Electromagnetic Waves**: In a coaxial cable, the electromagnetic waves travel at a speed determined by the dielectric material between the inner and outer conductors. This speed is slower than the speed of light in a vacuum (or air), which is approximately $3 \times 10^8$ m/s.
- **Velocity Factor**: The velocity factor (VF) of a coaxial cable is typically less than 1, indicating that the wave travels slower than in free space. The electrical length is calculated based on this reduced speed, making the effective length longer than the physical length.

### Why the Other Choices are Incorrect:
- **A: Skin effect is less pronounced in the coaxial cable**: 
  - The skin effect refers to the tendency of alternating current (AC) to distribute itself within a conductor such that the current density is largest near the surface. This does not directly relate to the electrical length of the cable.
  
- **B: Skin effect is more pronounced in the coaxial cable**: 
  - While the skin effect can be more pronounced in certain high-frequency applications, it does not affect the propagation speed of electromagnetic waves in the cable. Thus, it does not explain why the electrical length is longer.

- **C: Electromagnetic waves move faster in coaxial cable than in air**: 
  - This statement is incorrect. As mentioned, electromagnetic waves actually move slower in coaxial cables due to the dielectric material, which contradicts this choice.

### Useful Formulas and Rules of Thumb:
- **Velocity Factor (VF)**: The velocity factor can be calculated as:
  $$ VF = \frac{c}{v} $$
  where:
  - $c$ = speed of light in vacuum ($\approx 3 \times 10^8$ m/s)
  - $v$ = speed of the wave in the coaxial cable

- **Electrical Length**: The electrical length ($L_e$) can be expressed as:
  $$ L_e = \frac{L_p}{VF} $$
  where:
  - $L_p$ = physical length of the coaxial cable

This understanding of how electromagnetic waves propagate in coaxial cables is crucial for grasping concepts related to transmission lines and their behavior in radio frequency applications.