In 1705, the scientist Francis Hauksbee demonstrated that in a rotating glass globe with internal vacuum like in a barometer, filled with mercury, and statical charged by holding a hand against the rotating globe, a light phenomenon occurred, so bright that one could read a paper.
By 1705, Hauksbee had discovered that if he placed a small amount of mercury in the glass of his modified version of Otto von Guericke’s generator, evacuated the air from it to create a mild vacuum and rubbed the ball in order to build up a charge, a glow was visible if he placed his hand on the outside of the ball. This remarkable discovery was unprecedented at the time.
The idea behind Hauksbee’s generator is that a triboelectric (electrostatic) effect arises from sliding hands on a spinning glass. The voltage generated ionizes the gases in the globe, creating a blue plasma glow inside (An example can be seen in a modern-day Hauksbee static generator on YouTube).
Hauksbee’s early generators produced enough light to read by, and with their ionizing voltages they were true forerunners of our mercury vapor lamps. The big difference was that they were powered not by a utility voltage but rather by static electrical energy produced locally by friction of two dissimilar materials.
The underlying physics was relatively simple. A static charge can be produced by rubbing two objects – wool and amber for example.
Normally, matter is electrically neutral. In its atoms, the electrons and protons are equal in number. If an atom acquires excess electrons, it becomes negatively charged. If it loses electrons, it becomes positively charged. When two dissimilar materials are rubbed together, one of them may lose electrons and the other may gain electrons so an electrostatic differential appears between them.
How readily materials gain or lose electrons depends upon their place in the triboelectric series. This is a list of materials ranked in order of propensity for gaining or losing electrons. Materials whose atoms are more likely to give up electrons are at the positive end of the series and materials whose atoms want to gain electrons are at the negative end of the series.
Needless to say, this activity takes place in the outermost, or valence shell containing electrons with the highest energy. Reactions that involve electrons residing in other than the valence shell are nuclear, rather than electrical or chemical. The way to look at it is that the act of rubbing the materials together amounts to injecting energy into the system, and this results in the accumulation of an electrostatic difference of potential.
Some materials near the positive end of the triboelectric series are glass, Nylon and wool. Steel is neutral. Vinyl, silicon and Teflon are at the negative end. Materials that are farther apart in the triboelectric series have greater propensity to develop an electrostatic charges when rubbed together.
Definition: [plázmə] a hot ionized gas made up of ions and electrons that is found in the Sun, stars, and fusion reactors. Plasma is a good conductor of electricity and reacts to a magnetic field, but otherwise has properties similar to those of a gas. (source: Microsoft Encarta Dictionary)
|Courtesy NASA – click for larger image||In the world of physics it’s also known as the fourth state of matter, and is the closest we can get to “seeing” electricity. Extreme temperatures or electrical excitation strip electrons from their normal orbit around the atom’s nucleus. This condition of free electrons allows electrical current to flow easily, and gives off electromagnetic energy when the electrons fall back to their normal orbits. A good example of this is the bright orange glow from a neon gas filled sign. There are many natural examples of plasma in our world, and many fun and practical uses as well. We’ll try to explore some examples of both types below.|
Plasma lamps are a family of light sources that generate light by exciting a plasma inside a closed transparent burner or bulb using radio frequency (RF) power. Typically, such lamps use a noble gas or a mixture of these gases and additional materials such as metal halides, sodium, mercury or sulfur. A waveguide is used to constrain and focus the electrical field into the plasma. In operation the gas is ionized and free electrons, accelerated by the electrical field, collide with gas and metal atoms. Some electrons circling around the gas and metal atoms are excited by these collisions, bringing them to a higher energy state. When the electron falls back to its original state, it emits a photon, resulting in visible light or ultraviolet radiation depending on the fill materials.