120. When is Earth an Insulator and when a Conductor?
Why is it that Earth some times behaves like a conductor and some times behaves like a dielectric (=insulator)? Please answer this question..
I am a student of telecommunication, from Pakistan.
Reply
My work experience is with the magnetic field of Earth in space, so please check what I write with someone more experienced! Also, your question is not very specific--one must guess what you mean each time you write "sometimes." Still, let me try.
Sometimes the Earth is like a conductor--for instance, when you ground an instrument by running a wire from it to pipes in the ground. That is probably ionic conductivity--caused because earth usually has SOME water in it, coating its grains of clay or sand. That water is never pure (like distilled water) but always has at least some salt dissolved in it, and maybe other "electrolytes" as well.
Such dissolved molecules break up into electrically charged components, which can conduct electric charge (see http://www.phy6.org/Education/whposion.html) The current may consist of many branches, but the ground is so big that it can easily conduct even large currents.
But at other times you have radio signals, and the ions in the ground cannot oscillate fast enough to follow the voltage changes of such signals. In that case, Earth is like a dielectric. If you sit inside a concrete house during a rainstorm (and concrete is like earth, it also absorbs water), you can still listen to the radio inside. Put the radio inside a closed metal pot and the sound stops, because metal is a different kind of conductor and blocks radio waves from reaching the receiver.
That, anyway, is my guess
Good luck in your studies!
121. Can atmospheric atoms join the solar wind?
When atmospheric molecules of any type are dissociated from their home planet, for example Venus, are those molecules then blown outward by the solar wind? If so, could they be captured by other planets?
Could ice blocks on the Moon, or material on Earth, come this way from closer to the Sun?
Reply
Any atmospheric molecule removed from the gravity of its planet needs two additional steps before it can be caught up by the solar wind: it must become ionized (lose at least one electron, so that it responds to electric and magnetic forces), and be detached from whatever magnetic field it is produced in, so that it can attach itself to the interplanetary field which permeates the solar wind (see
http://www.phy6.org/Education/wimfproj.html
about attachments of ions to magnetic field lines).
That's what seems to happen to many atoms and molecules evaporated off comets. They easily escape the comet's weak gravity, and since comets have no magnetic field of their own, when atoms become ions (by sunlight detaching an electron) they are already in the interplanetary magnetic field and are therefore easily "picked up." The same happened with the "artificial comet" of the AMPTE mission (late 1984 or early 1985), where the experimenters waited for the spacecraft to enter interplanetary space, then blew an explosive charge which scattered barium vapor. Barium atoms are easily ionized by sunlight and are promptly picked up by the solar wind.
It is very unlikely for ions from a planet to do so, except maybe from the outer atmosphere of Mars and Venus, where planetary magnetic forces are weak or absent. I know of no ice blocks on the Moon: any ice there would probably come from comet impact.
And once an ion is in the solar wind, its chances of hitting a planet are negligible.