I apologise for the wording of my question, it will no doubt come across as confusing. If there is anything you are unsure about please feel free to ask me.
As a radio wave moves further away from the source, attenuation takes place. Why is it when this attenuation takes place the amount of distance that the weak electrical field now covers increases, compared to when it was closer to the source (shown from the image)? Is there an equation that I can use to tell me this? (coulomb's law ). If you are still confused by what i am asking, i have attached an image. As you can see the inverse law is taken into account as the radio wave moves away from the source. My question is how do i find out the the area covered on the last step (When it is 1/9). I have searched through the internet but no equation seems to be giving me what i need. (I want to know the total area that the final 3d covers in the picture, the part where it has the letters A, not the distance from the original source).