[BBLISA] Gadgets, power lines, and health [OT]

[John P. Rouillard]

In message <Pine.LNX.4.44.0809081631310.498-100000 at citation2.av8.net>,
Dean Anderson writes:
>Radiated power decreases as the square of the distance.

Which is correct.

>So your .75watt
>cellphone radiates a lot more power 1/8 inch from your head than does a
>100megawatt powerline at a quarter mile. This sounds wrong to me for
>some reason-- the total radiated power doesn't change, but the farther
>away you are, the less power you can absorb--I'm thinking too much or
>not enough.. sigh... Monday. You get the idea, anyway.

The energy density you are exposed to is proportional to the area you
cover at a given distance. E.G. if you are at the distance of the
radius of a golf ball from a radiator radiating 1 unit of em radition,
you receive you are exposed to 1/2 the radiation (because the
radiation making a straight line from the antenna at the middle of the
golf ball through the surface of the golf ball will hit your
body). The radition heading out the other side of the golf ball is
going away from you and won't affect you.

The surface area of a sphere is 4 pi r^2 and you can see the area
increases with the square of the radius. Therefore the density also
falls of as the square of the radius.

Now think of a ball 1 mile in radius, the same amount of radition (1
unit) is generated but now it is diluted across the surface area of a
ball 2 miles in diameter. Stand against the side of the ball and you
cover a very small area compared to the entire surface area of the
ball, so your exposure is reduced proportionately.

>If you want to play some math games, suppose you have a 100megawatt
>power line. Most of the power is transmitted to the other end. Some
>power is lost due to heating of the power lines. What remains is the
>power available for radiation at 60Hz on a long cylindrical copper
>conductor.  But remember to radiate an em wave, you also need to
>impedance-match free space somewhere.  All this could be calculated from
>first principles, and I think one will find very little energy is
>available to be radiated by a power line.

IIRC most transmission power lines are balanced pairs which actually
has the field density fall off as the cube of the distance and not the
square (because of cancellation factors in the coupling of the
cables), but it's been a long time since emag 2.

>I suggest you sit in on 6.071.

No don't do that to the poor guy.

--
				-- rouilj
John Rouillard
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My employers don't acknowledge my existence much less my opinions.