If I stuck two earth rods in a uniform field (e.g. a big flat area with grass or whatever) at ever increasing distances (e.g. 10m, 20m, 30m ..., 1000m etc) how would the result vary as a function of distance? An obvious answer would be linear (i.e. of the form R = AL + B where B is the resistance of the rods themselves). But a field isn't a wire, it's a plane - and that's a bit beyond my intuition, and beyond any easy maths.
Yep I reeckon Broadage has given the essence here. Good answer.
The earth is not a big thick highly conductive metal plate.
Is is composed of tiny lumps of soil, rock etc.
Each lump in itself is quite resistive.
However your rods are attached to loads of lumps. Each one is connected to a few other lumps.
Imagine each lump as a tiny ball-bearing of high resistance in a container all pressing on each other.
From any two points you`d have lots of series parallel and parallel series connections. Therefore the further away you get the resistance becomes nearer to zero.
Very near each rod etc the rods have the highest resistance.
If you draw a diagram with say two standard 4` rods say 8` apart and then draw a triangle about the length of each rods with curved sides you`d see the "resistance mountain" as a graph. Draw a second diagram with the rods 1 mile or 10 miles or 1000 miles or more apart and the resistance between the rods would be substantially the same in all cases.
Yep I reeckon Broadage has given the essence here. Good answer.
The earth is not a big thick highly conductive metal plate.
Is is composed of tiny lumps of soil, rock etc.
Each lump in itself is quite resistive.
However your rods are attached to loads of lumps. Each one is connected to a few other lumps.
Imagine each lump as a tiny ball-bearing of high resistance in a container all pressing on each other.
From any two points you`d have lots of series parallel and parallel series connections. Therefore the further away you get the resistance becomes nearer to zero.
Very near each rod etc the rods have the highest resistance.
If you draw a diagram with say two standard 4` rods say 8` apart and then draw a triangle about the length of each rods with curved sides you`d see the "resistance mountain" as a graph. Draw a second diagram with the rods 1 mile or 10 miles or 1000 miles or more apart and the resistance between the rods would be substantially the same in all cases.
