Deep Dive: T0C05
The correct answer is D: The human body absorbs more RF energy at some frequencies than at others. Exposure limits vary with frequency because the human body absorbs more RF energy at some frequencies than at others. The body acts like an antenna, resonating at certain frequencies (around 30-300 MHz for adults) where it efficiently absorbs RF energy. At these frequencies, exposure limits are lower (more restrictive). At other frequencies, absorption is less efficient, so limits are higher. For amateur radio operators, this explains why 6 meters has stricter limits than HF or UHF.
Why Other Answers Are Wrong
Option A: Incorrect. Lower frequency RF fields have less energy, not more. Higher frequencies have more energy per photon, but that's not why limits vary - it's about absorption efficiency. Option B: Incorrect. Lower frequency RF fields do penetrate the body - the issue is absorption efficiency, not penetration. The body absorbs RF differently at different frequencies. Option C: Incorrect. Higher frequency RF fields aren't 'transient' - all RF is continuous wave. The variation is about absorption efficiency, not transience.
Exam Tip
Exposure limits vary = body absorbs RF differently at different frequencies. Think 'B'ody 'A'bsorbs = 'B'est around 30-300 MHz. Body acts like antenna, resonating at certain frequencies where it efficiently absorbs RF. This determines exposure limits.
Memory Aid
Exposure limits vary = body absorbs RF differently. Think 'B'ody 'A'bsorbs = 'B'est around 30-300 MHz. Body resonates at certain frequencies, efficiently absorbing RF. This determines how restrictive exposure limits are.
Real-World Example
Your body efficiently absorbs RF energy around 50 MHz (6 meters) because your body size resonates at that frequency. At 3.5 MHz (80 meters), your body doesn't absorb RF as efficiently, so exposure limits are less restrictive. At 440 MHz (70 cm), absorption is also less efficient, so limits are higher. The variation in limits reflects how efficiently your body absorbs RF at each frequency.
Source & Coverage
Question Pool: 2022-2026 Question Pool
Subelement: T0C
Reference: 2022-2026 Question Pool · T0 - Safety
Key Concepts
Verified Content
Question from the official FCC Technician Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the T0C topic.