Download Mega avolts and Kil loamps s – The Life of fa Bolt t of

De
emonstrattion Megaavolts and Killoampss – The Life off a Boltt of Ligh
htning
Please notice
e: The electrical exp
perimentss in this de
emonstrattion have tthe poten
ntial to inteer‐
feree with sen
nsitive electronic eq
quipment. Visitors w
with pacem
makers or other ele
ectronic imp
plants sho
ould mainttain a distaance of 6 meters fro
om the staage which
h is marked by the rred linee on the floor. periments are very loud. Pleasse protectt your ears when th
his sign is SSome exp
illuminated. The Van‐‐de‐Graafff Generato
or In the Van
n‐de‐Graaff generator electrical ccharges aree sprayed on
nto a plastiic band which transpo
orts the chaarges upwards in
nto the hollow metal ball. Here tthe chargess cross overr to the mettal dome via an electrrical bridge. Like charges re
epel each other and th
herefore sp
pread out across the outerm
most surfacce of the baall. This makes space iin the center of tthe ball for more electtricity. The mechanicaal energy fro
om the band used in raaising the ccharges into
o the ball create
es the very high voltagges. Thee voltage risses and risees until the air, which is normallyy a bad con
nductor of eelectricity, breaks dow
wn. An eelectrical discharge th
hen occurs which neuttralizes the
e charge imbalance. If a grounded object is held neaar to the charged ball tthen sparkss can be produced. In dry air spaarks can be up to 50 cm
m in length
h, which corresponds to 500,000 Voltss. If a needle is placed
d near to th
he charged ball then th
he charges will be aattracted to
o the point. If a person is ccharged using the Van
n‐de‐Graaff generator,, then the ccharges sprread out ovver the surfface As all the ch
harges repe
el each otheer the effecct is literallyy a hair‐raissing of their body, including their hair. A
experience. Tech
hnoramastraasse 1, CH‐84
404 Winterth
hur Tel. +41 (0)52 24
44 08 44, Faxx +41 (0)52 2
244 08 45 info@
@technoram
ma.ch, www..technoramaa.ch © Swiss Scieence Center Technoramaa, Edition 07/2010, Mod
difications resserved
What is Plasma? When atoms and molecules are separated from some of their electrons, for instance through the influ‐
ence of a high voltage, the freed up ions and electrons can conduct electricity. When a gas is in this state we call it plasma. The stars are all made of plasma and on Earth we can see plasma in fluorescent lights, in lightning and in the Northern Lights. Before lightning strikes an initial almost invisible ion discharge rises from the ground. The main lightning bolt takes place when a plasma channel has connected the ground with the cloud. The lightning is then visible as blinding white spark. When a large current flows through plasma a strong magnetic field is produced which prevents the gas molecules from spreading out. Due to this magnetic constraint and the high temperatures a very large pressure is produced. When the current ceases the magnetic field disappears and the air expands explosively, producing thunder. Wimshurst Machine (Influence Machine) All objects contain positive and negative charges. If there are equal quantities of the two charges then the object is electrically neutral. Small irregularities in this distribution can lead to the movement of charges because similar charges repel each other and opposite charges attract each other. If a positively charged object approaches another object then the negative charges in the second object are attracted to the positive object so that the near side becomes negatively charged. At the same time only the positive charges remain at the far side as they can’t be moved as easily as the negative charges. As a result, the second originally neutral object gains a positive charge on the far side. This effect is called influence. In the Wimshurst machine there are two glass discs with attached metal foil patches which rotate in opposite directions. As the foil patches rotate small differences in charge are magnified through influ‐
ence and the excess charge is removed by a metal comb and stored in Leyden jars. As with the Van‐de‐ Graaff generator it is mechanical energy which through the rotation of the discs is converted into high voltage electricity. The separated charges are electrically connected to two metal balls and when the voltage is high enough a spark is produced between them. This machine can produce up to 700,000 Volts and sparks up to 70 cm in length. In the past Wimshurst machines were used to run X‐ray machines. With a diameter of over two meters this is the largest Wimshurst machine in the world.
Exploding Wire When electricity flows through the filament of a light bulb the wire heats up and begins to glow because of the electrical resistance. Here we can see what happens when 20 times as much voltage causes 2’000 times as much current to flow through a copper wire. When a large amount of electricity stored in a capacitor is forced through a copper wire in a very short amount of time then the metal heats up so much that it evaporates within a thousandth of a second with a big bang. The voltage (4,500 Volts) indicates what a large amount of energy each electron contains. The Current (1,000 Amps) indicates what a great number of electrons pass through the wire. The bang is caused by the air which is heated explosively and the hot plasma channel sends out a flash of light. Can Crusher A very large electrical current flows through the thick copper coil. This produces an electric and a magnetic field around the coil. An aluminum can is placed in the coil. The electrical field induces a current in the can which then produces its own magnetic field opposing the magnetism of the coil. The copper coil and the can then repel each other and the flimsy aluminum can is crushed by the forces produced. Plasma Ball Although there have been many reports of ball lightning scientists still struggle to reproduce the phenomenon and are undecided as to whether it really exists. In this experi‐
ment we simulate a lightning strike in wet earth. At the bottom of the glass container there is a ring electrode. In the middle there is a small ceramic tube above the sur‐
face of the water with an electrode at the center. During the electrical discharge plasma forms and rises out of the water. Could this be the same as ball lightning? Tesla Coil Tesla coils can produce very high frequency, high voltage AC electricity. The polarity changes up to 140,000 times per second. The high voltages ionize the air and cause very long sparks. Our Tesla Coil produces 1.2 million Volts and “bolts of lightning” of up to three meters in length. The noise is caused by the air heating up and the corres‐
ponding pressure fluctuations. The explainer clothed in chain mail and the visitors in the metal faraday corridor can safely catch the sparks in their hands using chain mail gloves. This works because the electricity remains on the outside of so called “Faraday cages” made of conducting metal. When the explainer holds a fluorescent tube in their hand it appears to light up of its own accord. The high voltages ionize the atoms in the tube which then produce light. Singing Tesla Coil This little Tesla coil makes music. The sparks heat up the air which then expands and produces a sound. A loud‐
speaker makes sound with a moving membrane. If the membrane moves 500 times a second then we hear a sound with a tone of 500 hertz. The same happens when the singing Tesla coil sparks discharge 500 times a second. The sparks act as a loudspeaker membrane and produce a recognizable sound. Incidentally: Hi‐fi fans swear by plasma tweeter loudspeakers because they have a very small moving mass and therefore reproduce high frequency sounds very well.