Deep Dive: E9F03
The correct answer is D: Electromagnetic waves move more slowly in a coaxial cable than in air. The electrical length of a coaxial cable is longer than its physical length because electromagnetic waves move more slowly in a coaxial cable than in air. The slower velocity means the wave takes longer to travel the same distance, making it electrically longer. Electrical length is measured in wavelengths or degrees. Because waves travel slower in coax (due to the dielectric), a given physical length represents more electrical length than the same physical length in air. For example, if a wave travels at 66% of light speed in the cable, a 10-meter physical length is electrically equivalent to about 15 meters in free space. The electrical length is longer because the wave is slower - it takes more time (more phase) to travel the same physical distance.
Why Other Answers Are Wrong
Option A: Incorrect. Skin effect doesn't make electrical length longer. Skin effect affects conductor resistance at high frequencies, not wave velocity or electrical length. Option B: Incorrect. More pronounced skin effect doesn't explain longer electrical length. The issue is wave velocity, not skin effect. Option C: Incorrect. Waves don't move faster in coax - they move slower due to the dielectric. This slower velocity makes electrical length longer than physical length.
Exam Tip
Electrical length > Physical length because waves are slower. Remember: Electrical length is longer than physical length because electromagnetic waves move more slowly in coaxial cable (due to dielectric) than in air.
Memory Aid
**E**lectrical **L**ength **L**onger = **W**aves **S**lower (think 'ELL = WS')
Real-World Example
You have a 10-meter piece of coax with velocity factor 0.66. The wave travels at 66% of light speed. Electrically, this 10-meter cable is equivalent to about 15 meters in free space because the slower wave takes more phase (more electrical length) to travel the same physical distance. The electrical length is longer because the wave is slower.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E9F
Reference: FCC Part 97.3
Key Concepts
Verified Content
Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E9F topic.