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

### Explanation:

1. **Why the correct answer is correct:**
   - The electrical length of a coaxial cable is longer than its physical length because electromagnetic waves travel more slowly in the cable than in free space (air). This is due to the dielectric material inside the coaxial cable, which slows down the propagation of the waves. The speed of electromagnetic waves in a medium is given by:
     $$ v = \frac{c}{\sqrt{\varepsilon_r}} $$
     where:
     - $v$ is the speed of the wave in the medium,
     - $c$ is the speed of light in a vacuum (approximately $3 \times 10^8$ m/s),
     - $\varepsilon_r$ is the relative permittivity (dielectric constant) of the medium.

   - Since $\varepsilon_r > 1$ for any material other than vacuum, the speed $v$ is less than $c$, making the electrical length longer than the physical length.

2. **Why the other choices are incorrect:**
   - **A: Skin effect is less pronounced in the coaxial cable**  
     - Skin effect relates to how current is distributed in a conductor at high frequencies, not to the speed of wave propagation. It does not affect the electrical length of the cable.
   
   - **B: Skin effect is more pronounced in the coaxial cable**  
     - Similar to choice A, skin effect does not influence the speed of electromagnetic waves in the cable, so it does not affect the electrical length.
   
   - **C: Electromagnetic waves move faster in coaxial cable than in air**  
     - This is incorrect because electromagnetic waves actually move slower in a coaxial cable due to the dielectric material, as explained above.

### Useful Rule of Thumb:
- The velocity factor of a coaxial cable, which is the ratio of the speed of the wave in the cable to the speed of light in a vacuum, is typically less than 1. This factor is used to calculate the electrical length:
  $$ \text{Electrical Length} = \frac{\text{Physical Length}}{\text{Velocity Factor}} $$

Understanding these concepts will help you grasp why the electrical length is longer and how wave propagation is affected by the medium.