Two Questions. Both involving plasma bulbs.

Question

Question 1: Why is it that when a flourescent bulb touches or is placed withing 3 inches or less of a plasma globe, it lights up? I did some research on plasma bulbs and the metal ball in the center of the globe is an electrode with a voltage ranging from 2 to 5 kilovolts. I have been using 110 amps. When voltage is applied to the electrode, it creates an electic field between the electrode and the glass globe. The jets are plasma (although thats kind of obvious) and attain their certain color because of the various noble gasses inside. The gasses are kept under pressure (All I could find was "medium" pressure, so I'm assuming thats something around 5 atmospheres?) and that means more collisions with electrons shooting out from the electrode. There you go, info on the plasma ball. Flourescent bulbs contain mercury vapor, which when hit with electrons emmit UV and visible light, the coating on the inside of the bulb absorbs UV and reemits as visible light. This takes place when an electric current is sent through the bulb. I have provided this information here so you don't have to do much extra research. Sorry if I wasted your time.... Anyhow, yea why does the bulb light up even when its not touching the plasma globe? I also noticed that if you stick a battery with the negative side towards the plasma globe very close to the bulb it will stop the bulb from lighting up, and if you take the battery away it lights up again.... just a side note I guess.

 

Question 2: How do you calculate the average temperature of something based on the color of light it emits? I know about black body radiation, but I don't really know how to calculate the temperature based on the color or the color based on the temperature. I was experimenting with magnets and electrically conductive materials on a plasma globe when I noticed that there is a grounding of electrons when you provide a path (touching the magnet.) I placed a magnet (or any sort of conductive material; copper, steel, iron, etc.) on top of the plasma globe and then very lightly touched it. There was a static electric bolt that went from the magnet to my finger and (because this is obviously grounding) I assume when into the rest of the house. Now, the interesting thing is that this doesn't happen without the metal there. But to get back to my question. I set up a tripod so I could have a sustained spark (it was hard, it needed to be within 1/5 mm but not actually touching it) and observed it was indigo. How can I figure out the temperature of the bolt with blackbody radiation on the basis of it's color? Thank you. 

 

PS: Even if the bolt's color was not caused by blackbody radiation, I would still like to be able to calculate somethings temperature on the basis of its color using blackbody radiation. (I'm assuming it would be done with x as the wavelength in nanometers or micrometers.

Answer 1

Question 1)

 

There is a very high voltage field with very low currents inside the bulb as you learned.  Currents pass through he plasma and light up.  Put you hand near the the globe and the arcs change because to disturb the field.  Just because the arcs are contained inside the globe by the gasses being only in the globe does Not mean the electric field is only in the globe.  When your hand approaches it you (your 98% water of a body) provides a large conductor in the electric field changing the field lines.  (Like a metal object in an electric field will perturb the field.)  You body is also fairly well grounded unless you take special care to wear insulating shoes, stand on insulation, or something.  [[Ben Franklin used to make his guests at parties stand on paraffin blocks to insulate them so he could charge them up and they could play party games, like the electric kiss, or drinking a charged up glass of wine - Old Ben was a party animal.]]  So your body also provides a path to ground and these (very low) currents pass through you unnoticed.

 

So now you take a florescent bulb in your hand.  Normally there is a high voltage 'plasma' arc in the bulb and the mercury emits UV light.  The phosphors on the bulb are energized by the UV and phoress (sic ?) a white light.  Different phosphors are used and you get cool white, day light, warm white, and other special colors for stores to male clothing look good, or make meat look nice and red without heating it.

 

When the florescent bulb enters the electric field a field is set up on and in the bulb.  Your body provides the path to ground for the low currents.  The field excites the phosphors (??either directly or my exciting the Hg gas inside ??) and they glow.  The area around you hand would not have a large enough voltage (due to your body grounding the field) and so the tube would not light on its whole length. 

 

I suspect that the battery is just providing a large sink (place for the field to go) for the field and like the bulb not lighting near your hand, it doesn't light near the battery terminal too.  I also suspect that is the plasma globe was reversed so that the center electrode had the opposite polarity then putting the (+) end of the battery near would do the same thing.

IMPORTANT <DO NOT DO IT, unless you are Very Well Trained in the engineering - it could be very dangerous if done wrong!>

 

Question 2)

 

I think you want Plank's Law:

 

I_v = (2hv³/c²)( 1/ (e^(hv/kT)-1)

 

NOTE: The v's are NOT v's they are the Greek letter nu (ν)

 

ν=nu=wavelenght 

h=Plank's constant

k=Boltxman's constant

c=speed of light

T=temperature

I_v=Intensity (energy emitted per unit surface per unit time per unit solid angle and in the frequency range between v and v + dv

 

T_b = (hv/k) ln^-1(1+(2hv³/I_vc²))

 

if hv << k

 

T_b = (I_vc²)/(2kv²)

 

for narrow band where delta(v) << v  and known I

 

T_b = (Ic²)/(2kv² [delta]v)