At which of the following frequencies does maximum permissible exposure have the lowest value?

• A. 10 MHz
• B. 25 MHz
• C. 50 MHz
• D. 100 MHz

Answer: (C)

The maximum permissible exposure (MPE) levels for radio frequency (RF) radiation are defined based on the specific frequency of the signals. As frequency increases, particularly in the range of a few MHz to several hundred MHz, the human body becomes more susceptible to absorbing RF energy, which can lead to biological effects.

At 50 MHz, the MPE values are lower compared to the other frequencies listed because the frequency is closer to the range where the human body's interaction with electromagnetic fields becomes more pronounced. This range of frequency can result in more significant heating effects on the human body tissues. As the frequency increases beyond a certain point, the MPE generally tends to decrease until it reaches a threshold where changes in the absorption characteristics begin to stabilize.

In contrast, at frequencies like 10 MHz and 25 MHz, the MPE values are higher. The absorption of RF energy by biological tissues is less efficient at these lower frequencies, resulting in higher permissible exposure levels. By 100 MHz, while it does show significant changes in absorption characteristics, the pattern indicates a lower permissible exposure level as the frequency continues to rise, but it is not as low as at 50 MHz.

Thus, the maximum permissible exposure values represent the lowest point at 50 MHz in