Deep Dive: E3A10
The correct answer is D: The index of refraction. What determines the speed of electromagnetic waves through a medium is the index of refraction. The index of refraction determines how fast EM waves travel in a medium. For amateur radio operators, this is important for understanding propagation. Understanding this helps when working with different media.
Why Other Answers Are Wrong
Option A: Incorrect. Resistance and reactance don't determine wave speed - index of refraction does. Resistance/reactance isn't the factor. Option B: Incorrect. Evanescence doesn't determine wave speed - index of refraction does. Evanescence isn't the factor. Option C: Incorrect. Birefringence doesn't determine wave speed - index of refraction does. Birefringence isn't the factor.
Exam Tip
EM wave speed in medium = determined by index of refraction. Think 'E'M wave 'S'peed = 'I'ndex of 'R'efraction. The index of refraction determines how fast EM waves travel in a medium. Not resistance/reactance, not evanescence, not birefringence - just index of refraction.
Memory Aid
EM wave speed in medium = determined by index of refraction. Think 'E'M wave 'S'peed = 'I'ndex. The index of refraction determines how fast EM waves travel in a medium. Important for understanding propagation.
Real-World Example
The speed of electromagnetic waves through a medium: It's determined by the index of refraction of that medium. For example, in air (index ≈ 1), waves travel at nearly the speed of light. In other media with higher indices, waves travel slower. This is what determines the speed - the index of refraction.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E3A
Reference: 2024-2028 Question Pool · E3 - Radio Wave Propagation
Key Concepts
Verified Content
Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E3A topic.