Plasma and Conservation Laws
Date: Spring 2013
Plasma is formed when a region of elements become ionized. In my lay person's terms, Energy comes in, forcing electrons to jump ship en masse. This mass flow of electrons looking for new homes, and atoms looking to absorb new electrons creates the dazzling plasma display. This can be demonstrated with applying a high frequency coil to a bulb or other vacuum tube. "Poof" plasma, lightning in a bottle, or mini-sun.
I am doing a star gazing field trip with my students where I will apply a high frequency coil to a light bulb to make plasma, and I want to be prepared for the following questions: What causes the light? Is is the energy released when the electron leaves the atom, or when the electron finds a home? (Or is it something else). Heat is released as well, where is this coming from? Is it the excess energy from the high frequency coil, or is heat coming from the atomic reactions? Is there a diagram somewhere that shows the conservation of energy and mass?
Your analogy of electrons “looking” for a home, is not at all bad nor is it inaccurate. Let us put a little more detail on it. Light (or any other electromagnetic radiation) is emitted when an electron (or other particle for that matter -- but let us stick to light to keep things simple) “falls” from a state of higher energy to a state of lower energy. The change in energy may (or may not) allowed energy levels within an atom, or may involve an energy state of an atomic ion. In the most simple terms, it does not matter how you get the electron “excited” to a higher energy, before the electron “falls” into a state of lower energy. The key issue is the “decay” of the electron from a state of higher energy to a state of lower energy. Again, the exciting tool can be a flame, a beam of high energy electrons, collisions between atoms, or a microwave cavity … In any case it is a tool to excite the electrons to a higher energy state followed by a “decay” to a lower energy state, emitting a photon.
The excess energy comes from the exciting source – again a flame, collisions, or other source of energy. That’s where the “excess energy” comes from. You can find tabulations of “allowed” transitions (Which ones are “allowed” is a whole other topic, too large for this short answer.) in a reference such as:
http://physics.nist.gov/PhysRefData/ASD/levels_form.html As you can tell the energy levels are abundant!!
I am not a specialist in this field, but I have some doubts as to whether you can produce a plasma stream with a high frequency coil and a light bulb.
Plasma is a mass of charged ions and free electrons, so how can you form a plasma in a vacuum?
You need a gas, a source of high energy to disassociate the electrons from the ions (like a laser), and you need a magnetic field to contain your plasma in.
A high frequency coil will produce an oscillating magnetic field. To magnetically confine a plasma you want a strong consistent magnetic field so you will not lose your ions radially and encourage them to remain in a stream. So I do not think a high frequency coil is what you need. Here is a reference:
If you did achieve a plasma, where would the light come from?
I think you are trying to create a nuclear fusion reaction in a light bulb.
Light and energy comes from nuclear fusion reactions in that two atoms combine to form a third different atom, the third atom weighing less than the sum of the two colliding atoms. Then, the missing mass is released as energy according to the formula E = m C2.
If you do achieve a plasma, you need to be wary of radiation from light, radio waves, X-Rays and Gamma Rays. Here is an example of what you are dealing with from this article:
Lightning is an example of plasma present at Earth's surface. Typically, lightning discharges 30,000 amperes at up to 100 million volts, and emits light, radio waves, X-rays and even gamma rays. Plasma temperatures in lightning can approach ~28,000 Kelvin and electron densities may exceed 1024 mâˆ’3
You can make a neon tube glow using an electro-magnetic field generated by a coil. The energy of the electromagnetic (EM) field kicks electrons on the neon atoms up to higher energy levels, then when they fall back down to their original orbits they emit light. The energy for this action comes from the power supply that powers your coil that stimulates the electrons in the first place. The equation for the conservation of mass and energy is E = m C2. I do not recommend you do this on your own because you have no idea of the magnitude of the fields you are generating and you could hurt yourself or somebody else.
Light is emitted when the electrons jump back DOWN to a bound state in an atom. That is because they give off energy (as light) to enter that lower-energy state. They have to be GIVEN energy to escape their atoms. That comes from the high electric field or from high temperature, depending on how the plasma is generated.
Heat is released because the different ions are constantly running into their container, transferring kinetic energy to it. When the container atoms move faster, that?s higher temperature. So basically the ?heat? given off is one of the ways the kinetic and potential energy in the plasma dissipates to the surroundings.
Richard E. Barrans Jr., Ph.D., M.Ed.
Department of Physics and Astronomy
Thanks for the questions. Just so you are aware, the plasma in a neon sign is not a "mini-sun" as there are no nuclear reactions taking place.
If you use a standard incandescent light bulb, your high frequency coil will cause the light bulb to be lit up. I suspect you may be using a high frequency coil to illuminate a neon-filled bulb.
Light is caused by electrons moving from high energy orbits to low energy orbits. When the electrons make this jump, they release energy in the form of light. The light can be absorbed by the material and its electromagnetic energy is converted into heat.
Theoretically, you are converting a very, very, very little amount of mass into energy, but this is too small to be measured. For this demonstration, I would not bring in the concepts of the equivalence of mass and energy. I think it would confuse your students.
I hope this helps. Please let me know if you have more questions.
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Update: November 2011