Electromagnetic waves become weaker with distance due to the phenomenon known as "inverse square law" or "inverse square relationship." According to this law, the intensity of a wave decreases as the square of the distance from the source increases.
The inverse square law applies to many physical phenomena, including the propagation of electromagnetic waves. It states that the power per unit area carried by a wave decreases as the distance from the source increases. This is because the energy carried by the wave spreads out over an increasingly larger area as it moves away from the source.
Mathematically, the relationship can be expressed as:
Intensity ∝ 1/distance²
Where "Intensity" refers to the power per unit area of the wave, and "distance" represents the distance from the source.
This means that if you double the distance from the source, the intensity of the wave will decrease to one-fourth (1/2²) of its initial value. Similarly, if you triple the distance, the intensity will decrease to one-ninth (1/3²) of its initial value, and so on.
As electromagnetic waves propagate outward from their source, the energy they carry spreads out over larger and larger spherical surfaces. This causes a dilution of the energy density and, consequently, a decrease in intensity with increasing distance. It's important to note that this weakening of the wave's intensity occurs in all directions around the source, not just in a single direction.
Therefore, the decrease in the intensity of electromagnetic waves with distance is a consequence of the spreading out of energy over a larger area as the wave propagates away from its source, following the inverse square law relationship.