MOTION MOUNTAIN

66 1 electricity and fields
Challenge 54 s
Challenge 55 s
Page 232
Challenge 56 e
Challenge 57 ny
Challenge 58 ny
for the coil, and thus for a transformer?
The picture also includes the transistor. This device, as the hydraulic component
shows, can be used to control a large current by using a small current. Therefore, transistors
can be used as switches and as amplifiers. This is the reason that all electronic
circuits,fromradiostomobilephonesandcomputers–makeheavy use of transistors. A
modern mobile phone or computer typically contains several million transistors, mostly
assembled inside so-calledintegratedcircuits.Thedesignofthesedevices is a science on
its own.
∗∗
There is even a way to push the previous analogy in another direction: it is possible to
produce a mathematically consistent analogy between electric circuits and continuous
fields. The required circuits are infinite grids or meshes in all directions of space, and
are called mimetic discretizations. If you like to think in electric terms, you might enjoy
pursuing this. Just search for the term on the internet.
∗∗
The ionosphere around the Earth has a resonant frequency of7 Hz; for this reason any
apparatus measuring low frequencies always gets a strong signal at this value. Can you
give an explanation of the frequency?
∗∗
The Kirlian effect, which allows one to make such intriguingly beautiful photographs, is
not a property of objects, but a result of the applied time-varyingelectricfield.
∗∗
At home, electricity is mostly used as alternating current. In other words, no electrons
actually flow through cables; as the drift speed of electrons in copper wires is of the order
of1 µm/s, electrons just move back and forward by20 nm. Nothing flows in or out of the
cables! Why do the electricity companies require a real flow of money in return, instead
of being satisfied with a back and forth motion of money?
∗∗
Do electrons and protons have the same charge? Experiments show that the values are
equal to within at least twenty digits. How would you check this?
∗∗
Charge values are velocity-independent, even near the speed of light. How would you
confirm this?
∗∗
Magnets can be used, even by school children, to climb steel walls. Have a look at the
www.physicslessons.com/TPNN.htm website.
∗∗
Can magnets be used to make a floating bed? In 2006, a Dutch architect presented to
Motion Mountain – The Adventure of Physics copyright © Christoph Schiller June 1990–November 2015 free pdf file available at www.motionmountain.net