What is Difference between EM Radiation and EM Field. Are They all are different quantities or interrelated with each other. Do they both follow inverse square law.Is light EM radiation or Field
First, what is an "EM field"?
At any point in space we can define an electric field (E field). It points in the direction that a positive charge would accelerate if we released it from that point. At any point we can also define a magnetic field (B field). It is a little more complicated, but for now let's just say it points in the direction that a compass needle would point if it was placed at this point in space.
So what we mean by an "electromagnetic field" is either or both the E field and the B field at a point.
We can cause a disturbance (such as by moving a charge back and forth) which causes the electric fields and magnetic fields at a point to oscillate. This disturbance is "self-propagating" which means that an oscillating E or B field at one location causes the E and B fields at nearby locations to also oscillate. So the disturbance travels. We call this travelling disturbance in the E and B fields electromagnetic radiation (because it "radiates" from wherever its source was). So EM radiation is not the same as EM field. It is a disturbance in the field which travels.
What we often mean by "light" is EM radiation which is visible to the human eye. More properly this is called "visible light".