點解freq. 越高既電磁波 就走得唔遠?

Who says that gamma ray has a range of 100 m? It is entirely NOT true.
Both gamma rays and radio waves are eelctromagnetic (EM) waves in nature. They both obey the same physical laws. The decrease in intensity of EM waves from a source follows the "inverse square law", i.e. doubling the distance from the source would lower the intensity by 1/4.
If no absorption occurs along the path of the EM wave, the wave can propagate to infinte distance. This is simply a result of the Law of Conservation of Energy.
In real practice, the maximum distance at which a wave (gamma ray or radio wave, or other waves) can travel in a mdeium depends on the absorption of the wave in that medium.
A simple example is that ultra-violet radiation is readily absorbed by the ozone layer at the upper atmosphere. But waves of high or lower frequenies, could penetrate through the atmosphere. This is because of the strong absorption of ozone to ultraviolet radiation.

因為波長短，所以走唔得遠，要行得遠，發送功率要勁大，例如微波爐所用微波基本上行唔到爐身外面。