Basic Qualification · B-003 Station assembly, practice and safety · B-003-021-008
How does the power density of an electromagnetic wave change as it propagates away from an antenna in free space?
- A It decreases linearly with the distance
- B It decreases in inverse proportion to the distance
- C It decreases at a rate depending on ground absorption
- D It decreases as the square of the distance
Correct answer: D — It decreases as the square of the distance. From the official ISED question bank, verified word for word.
Why
As an electromagnetic wave spreads out from an antenna in empty space, its energy covers a larger spherical area, causing the power density to drop rapidly. The full explanation — and one for every question — is in Pro.
Practise this section
Building a station safely: power supplies, grounding, RF exposure, lightning, feedline routing, and what a transmitter, receiver and transceiver actually do.