|MadSci Network: Physics|
Hi Timothy, Your question is really a 2-part'er; I'll try to answer both. Nikola Tesla was a man of many talents and ideas; some of which have come to pass, others still in the imagination of man. One of his most controversial fields of experimentation had to do with the theory that the Earth was a giant resonator. The theory is that the Earth is a (nearly)perfect conductor, covered by a thin dielectric; the atmosphere, that being covered by another conducting layer; the ionosphere. What you end up with is one huge capacitor! What you need to make a resonator is either a resistance/capacitance, or inductance/capacitance 'tank' circuit. In all probablity, the 'device' he used was the Earth as the capacitor and the building foundation as the resistor and/or inductor. According to most accounts, when he turned on the current and increased is slowly, the building he was in started to make cracking sounds. As he increased the current, the cracking sounds became louder, and the building began to shake. Hearing a commotion outside, he went to a window in the lab and looking out, saw people starting to panic. They evidently thought that an earthquake was in progress. He immediately told his assistant(s?) to shut it down, and destroy it and all the documentation. To this day, we don't know for sure whether his experiment was the cause of the 'earthquake", or merely a coincidence. You be the judge! Before you chalk it up to coincidence tho', bear in mind that his calculations of the Earth's resonant frequency have been proven to be very accurate! You also mentioned the effect of temperature being a factor in determining the resonance of a gas or solid. First, let's examine the definition of resonance in terms of chemistry (which you are alluding to), rather than physics. Resonance description is a representation in which you describe the electron structure of a molecule having delocalized binding by writing all possible electron-dot formulas. for example: If you take ozone, O3, you could write the electron-dot formula two different ways. They would look like this : : O and O (s) (d) (d) (s) :O: :O: :O: :O: : : (note: the (s) and (d) are actually written as a - or a = to denote a single or double bond; not the (s) or (d), as shown.) As you can see, the first example the leftmost O has a single bond to the central O and a double bond from the rightmost O. But in reality, it could be reversed, as in the second example. We cannot tell which is correct for a particular molecule of ozone, so we write a resonance formula to show that there are 2 or more possible combinations; all of which are correct. In the real resonance formula, the word "and" would be replace by a double- ended arrow such as <-------->. Now to get back to the resonant frequency of a material, you are right, Temperature and atmospheric pressure do affect it. An example might be Jello (tm). When you make Jello, you first dissolve the gelatin in hot water. This makes a watery solution which, if you were to drop a pebble into it, would form ripples representing the resonant frequency of the liquid. When cooled sufficiently, the Jello turns into a gel (a thixotropic substance - look it up!!) Now try dropping a pebble onto it's surface and you will see a different resonant frequency of the ripples. This change in resonant frequency is not due to the spacing of the electrons about the nucleus; rather it is due to the density of the substance - the distance between molecules. Thus, getting back to the 'earthquake machine', the resonant frequency of the Earth is extremely low, due to it's density. This phenomena has been put to good use by the Armed Forces by allowing Extremely Low Frequency (ELF) communications through the Earth' crust to points many thousands of miles away; indeed across the globe! This is done thru a series of extremely long antennae (many miles) buried within the ground. I hope this has helped answer your question. If you need further explanation, contact me through the MadSci network. Your not-so-mad scientist, Karl
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