MadSci Network: Other

Re: How does a Plasma Ball work?

Date: Sat May 2 13:35:09 1998
Posted By: David Winsemius, MadSci Admin
Area of science: Other
ID: 893896431.Ot

Those Plasma Balls are really fascinating. There is a high voltage source 
attached to the inner ball that causes a current to flow to the nearest point 
with a lower voltage. The ball is filled with a gas that glows when it has 
electricity flowing through it. When nothing is touching the ball, the current 
just flows anywhere onto the ball. When you touch the ball, some of the current 
can flow through the glass and into you. Because your body is providing a place 
for the current to flow, the electricity keeps flowing and the lines of current 
can stay connected to the point on the ball that you are touching.
See this site, 
Teaching Kids about Physics, which has information designed for science teachers.

This is what it says about Plasma Balls:
Plasma Ball 

Needed: Plasma Ball
        Fluorescent light bulb
Warnings: The plasma ball is usually harmless, but I would still recommend 
warning those with any type of heart condition.

What to do: Place your hand on different spots of the sphere. It will collect 
more "sparks" than the rest of the sphere. Also, place the fluorescent bulb next 
to the sphere. It should light up. By holding the bulb in different places, you 
can show that the electricity is actually moving from the sphere to you. If you 
hold the bulb in the middle, only half of it will light. On the other hand, if 
you hold the bulb at one end, the entire bulb should light up.

What to say: The plasma ball is the same concept as the Van de Graaff generator. 
Instead of discharging from a large sphere to a smaller one, the plasma ball 
discharges electricity from a small center ball to a larger surrounding sphere. 
The sphere is filled with a gas that emits light of different colors as 
electricity is passed through it.

The Physics: The plasma ball uses fluorescence to produce the different colors 
of light. Fluorescence occurs as electrons pass through and collide with the 
atoms of the gas inside of the sphere. As a result of the collisions, some of 
the atoms get raised to a higher energy level. Very quickly, usually about 10^-8 
seconds, the excited atoms will return to their normal energy states. 
This process involves the emission of a photon. Since the energy levels of a 
particular substance are very quantified, the photon emitted will have a 
particular energy. This particular energy produces light of a specific 
wavelength and thus a specific color. Einstein showed that photons of energy E 
will have a frequency, f, equal to E/h, where h is Planck's constant (6.63 x 10^
-34). The wavelength of the light can be found by wavelength = speed of light/ 

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