ELA Component

When my physics teacher chose my PBL experiments I was a little upset; I really wanted to choose my project myself, but it was too late, the decision was made, for the next months I was going to research and understand the Plasma Ball and the Radiometer. Nevertheless, I began to investigate about my two projects and soon I discovered that they weren't so bad, they were actually very interesting and fascinating.

First, I researched about the Plasma Ball. It was invented by the innovative scientist, Nikola Tesla.Tesla used an incandescent-type lamp globe with a single internal conductive element and excited the element with high voltage currents from a Tesla coil, which is an electrical resonant transformer circuit invented by himself, it is used to produce high-voltage, low-current, high frequency alternating-current electricity. Thus creating the brush discharge emanation. The spherical shape style of plasma globe was created later by James Falk and marketed to collectors and science museums.

Everybody has seen a plasma ball at least once in their life. Many tend to always place their finger on the plasma ball because the dynamic purple rays seem like a magnet to our finger whenever we touch a Plasma Ball, and it is very fascinating, through very few now the physics behind it. Placing a finger tip on the glass creates an attractive spot for the energy to flow, because conductive human body is more easily polarized than the dielectric material around the electrode (the gas within the globe) providing an alternative discharge path having less resistance. Therefore, the capacity of the large conducting body to accept radio frequency energy is greater than that of the surrounding air. This flow also causes a single filament, from the inner ball to the point of contact, to become brighter and thinner.

Much of the movement of the filaments is due to heating of the gas around the filament. When gas along the filament is heated, it rises, carrying the filament with it. If the filament is discharging into a fixed object (like a hand) on the side of the globe, it will begin to deform into a curved path between the central electrode and the object. When the distance between the electrode and the object becomes too great to maintain, the filament will break and a new filament will reform between the electrode and the hand.

The Radiometer is also a very interesting experiment. A radiometer is a device for measuring the power of electromagnetic radiation. Generally, the term radiometer denotes an ultraviolet detector yet it also includes detectors operating on any electromagnetic wavelength. The most famous example is the Crookes radiometer, an early-model device where there's a partial vacuum and a rotor that has four little vanes which are dark on one side, that spin when exposed to light. A common myth (one originally held even by Crookes) is that the momentum of the absorbed light on the black faces makes the radiometer operate. If this were true however, the radiometer would spin away from the non-black faces, since the photons bouncing off those faces impart even more momentum than the photons absorbed on the black faces.

The scientist, Reynolds, later disproved Crookes' theory by finding that if a porous plate is kept hotter on one side than the other, the interactions between gas molecules and the plates are such that gas will flow through from the cooler to the hotter side. The vanes of a typical Crookes radiometer are not porous, but the space past their edges behaves like the pores in Reynolds's plate. On average, the gas molecules move from the cold side toward the hot side whenever the pressure ratio is less than the square root of the (absolute) temperature ratio. The pressure difference causes the vane to move, cold (white) side forward.