On 3/9/2015 12:54 PM, Brian Reay wrote:
On 09/03/15 15:43, Jerry Stuckle wrote:
On 3/9/2015 10:11 AM, Jeff wrote:


As are basically all formulas. Even Ohm's Law was derived from actual
observations.


That is certainly not correct in a lot of cases. The inverse square law
for free space path loss, for example, is derived intuitively and simply
from the transmitted power being equally distributed in all directions,
not from observations.

S= P*(1/(4piD^2))

Jeff

Jeff,

Actually, not. It was observed first back in the 1700's-1800's when the
link between electricity and magnetism was being investigated. And
hundreds of years before that, it was a know property of magnets.

The equations didn't come until later.


You are confusing a magnetic field with an EM field. You can have a
magnetic field with no E field- eg from a bar magnet. It will have a
magnet field which exhibits the inverse square law but no E field.



Brian,

No, I'm not confusing the two. But my point is that one led to the
other. The equations didn't appear out of mid air - measurements
preceded them.

The observations I was talking about in the 1700's-1800's were for EM
fields. And my point was their loss with distance is the same as with M
fields - which had been known for a much longer time.

And E fields were also measured back in the days of Leyden jars and the
like.

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