Physics

The key is understanding how magnetic field lines spread out in space. Current creates concentric circular field lines around the conductor, and as you move farther away, those same field lines must stretch over an increasingly larger circle. Since the total "amount" of field (flux) is conserved, spreading it over a bigger perimeter means the field strength at any point must weaken—this is why $B \propto 1/r$. Think of it like light from a bulb: the same energy spreads over larger and larger spheres, so brightness dims with distance.

The key is understanding how magnetic field lines spread out in space. Current creates concentric circular field lines around the conductor, and as you move farther away, those same field lines must stretch over an increasingly larger circle. Since the total "amount" of field (flux) is conserved, spreading it over a bigger perimeter means the field strength at any point must weaken—this is why $B \propto 1/r$. Think of it like light from a bulb: the same energy spreads over larger and larger spheres, so brightness dims with distance.