MOTION MOUNTAIN

liquid electricity, invisible fields and maximum speed 55
capacitive head
(c.10-20 pF to earth)
c.1000 turns
large sparks
10-100nF
230 V
50 Hz
c.10 kV
50 Hz
spark gap
for switching
c.10 turns
resonance frequencies
100 - 500 kHz
ground
Challenge 35 s
Challenge 36 d
F I G U R E 23 The schematics, the realization and the operation of a Tesla coil, including spark and corona
discharges (photographs © Robert Billon).
tion: this is dangerous; that is the reason that such devices cannot be bought (almost)
anywhere.The basic diagram and an example is shown in Figure 23. Tesla coils look like
large metal mushrooms (to avoid unwanted discharges) and plans for their construction
can be found on numerous websites or from numerous enthusiast’s clubs, such as www.
stefan-kluge.de.
∗∗
In 1722, George Graham discovered, by watching a compass needle, that the magnetic
field of the Earth shows daily variations. Can you imagine why these variations occur?
∗∗
If even knocking on a wooden door is an electric effect, we should be able to detect fields
when doing so. Can you devise an experiment to check this?
∗∗
Birds come to no harm when they sit on unprotected electricity lines. Nevertheless, one
almost never observes any birds on tall, high voltage lines of100 kV or more, which
moted the polyphase alternating current system, the alternating current electric motor, wireless communication,
fluorescent lighting and many other applications of electricity. He is also one of the inventors of
radio. The SI unit of the magnetic field is named after him. A flamboyant character, his ideas were sometimesunrealistic;for
exampleheimagined that Teslacoils couldbeusedforwirelesspower transmission.
Motion Mountain – The Adventure of Physics copyright © Christoph Schiller June 1990–November 2015 free pdf file available at www.motionmountain.net