MadSci Network: Physics |
Dear Melissa: You ask many questions. To avoid confusion I will answer them one at a time. 1. We know the temperature of the sun by analyzing the wavelength of the light which is emitted from it. The wavelength of the light is a measure of the temperature so the temperature of the sun can be measured without having to go to the sun. 2. A plasma per se is a gas containing may ions and free electrons. A simple bolt of lightning in a thunderstorm is a giant plasma, which we see all the time. The gas which glows brightly which you see in the lightning is very hot-thousands of degrees- but the hot gas is confined to a very small volume and as you move away from the plasma the temperature drops very quickly. Without a constant voltage to drive electric current which is the heart of the plasma, then the plasma disappears. In lightning the voltage comes from the electrostatic charging of the clouds above the earth to a very high voltage, which then causes the electric spark to ground which is the plasma. But the bolt of lightning is the discharge of this high voltage, changing into the very high current of ions and electrons. The voltage then disappears and the plasma is gone! It happens so fast that the surrounding area does not have time to heat up before the voltage is all gone! Scientists create a plamsa by generating very high voltages which cause the gases to break down just like lightning, making the plasma. A simple neon sign is a plasma! That is a cold plasma! The temperature of the plasma depends on the pressure of the gas and the current flowing through it. When the pressure is low, as in a neon sign, the temperatures are low because the currents are low! Usually thay are less than one ampere. But a lightning bolt carries currents of thousands of amperes-big difference! The pressure is high (about 1,000 times the pressure in the neon sign). And it is not true that plasma forms rarely on earth. Every time there is a lightning bolt there is a plasma! Without the presence of a voltage to separate the positive ions and the free electrons, the positive and negative charges recombine to form neutral atoms. The opposite charges attract each other very strongly, so when the voltage is gone the plasma vanishes immediately by the recombination of the positive ions with the negative electrons. I hope this answers your questions. If you have more questions after this please ask them and I will explain in further detail for you. R. Bersin......
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