At what distance does the intensity of radiation decrease based on the inverse square law?

The correct answer emphasizes that the intensity of radiation diminishes with the square of the distance from the source, a principle known as the inverse square law. This law states that as one moves away from a point source of radiation, the intensity (or the amount of radiation reaching a given area) decreases in proportion to the square of the distance.

For example, if you double the distance from a radiation source, the intensity of radiation is not just halved; it is actually reduced to one-fourth of its original intensity. This mathematical relationship arises because the radiation spreads out over a larger area the farther it travels. The radiation emanating from a point source spreads isotropically (equally in all directions), so the intensity measured over a larger surface area decreases significantly.

In contrast, the other choices describe different phenomena. Linear decrease would imply a constant rate of decrease regardless of distance, which is incorrect. A constant intensity would mean that distance has no effect on radiation strength, which contradicts the nature of radiative decay over distance. Fluctuating intensity does not reflect the predictable and measurable behavior described by the inverse square law. Thus, the essential understanding here is that the inverse square law provides a reliable mathematical framework for predicting how radiation intensity changes with