ARRL Technician Practice Exam

Why do exposure limits vary with frequency?

1. The FCC regulates them differently

2. The human body absorbs more RF energy at some frequencies than at others

3. Different materials absorb RF energy differently

4. Frequency does not affect exposure limits

The correct answer is: The human body absorbs more RF energy at some frequencies than at others

The correct answer centers on the fact that the human body has varying levels of absorption for radio frequency (RF) energy depending on the frequency itself. This variation occurs due to the biological and physiological characteristics of the body, including the water content and the dielectric properties that change with frequency. At certain frequencies, the skin or other tissues may absorb more RF energy, leading to increased exposure levels and potential health effects. For instance, lower frequencies may penetrate the body more deeply but are generally thought to be less harmful than higher frequencies, which may be absorbed more readily and can lead to heating of tissues. This biological response is the reason why exposure limits are established differently for various frequency ranges, as they must account for the body's differing responses and risks associated with RF energy absorption. Understanding this relationship is crucial for ensuring safety in environments where RF energy exposure occurs, as different frequencies can have different potencies and biological impacts.