MOTION MOUNTAIN

104 3 what is light?
Page 84
gases change colour when subject to a field yielded several Nobel Prizes for physics. With
time, many more influences on light-relatedpropertiesbymattersubjectedtofieldswere
found. An extensive list is given below, in the table on page 216. It turns out that apart
from a few exceptions the effects canall be described by the electromagnetic Lagrangian
(51), or equivalently, by Maxwell’s equations (55). In summary, classical electrodynamicsindeed
unifies thedescriptionofelectricity,magnetismandoptics;all phenomena
inthesefields,fromtherainbowtoradioandfromlightningtoelectricmotors,arefound
tobedifferentaspectsoftheevolution of the electromagnetic field.
After two centuries of research, it became clear that light and radio waves form only
a small section of the full spectrum of electromagnetic waves, which contains the waves
from the smallest possible to the largest possible wavelengths.The full spectrum is given
in the following table.
TA B L E 14 The electromagnetic spectrum.
Fre - Wavelength
quency
Name Main
properties
Appearance Use
3⋅10 −18 Hz10 26 m Lowerfrequencylimit see the section on cosmology
30 Mm Quasistaticfields intergalactic,
galactic, stellar and
planetary fields,
brain, electrical fish
10 Hz–
50 kHz
50 –
500 kHz
500 –
1500 kHz
1.5 –
30 MHz
15 –
150 MHz
30 Mm–
6 km
6 km–
0.6 km
Radiowaves
ELW go round the
globe, penetrate
into water,
penetrate metal
LW
600 m– MW
200 m
200 m–10 m SW circle world if
reflected by the
ionosphere,
destroy hot air
balloons
20 m–2 m VHF allow battery
operated
transmitters
collaborator ofWilliam Thomson.
electronic devices
nerve cells,
electromechanical
devices
follow Earth’s emitted by
curvature, felt by thunderstorms
nerves (‘bad
weather nerves’)
reflected by night
sky
emitted by stars
emitted by Jupiter
power transmission,
accelerating and
deflecting cosmic
radiation
power transmission,
communication
through metal walls,
communication with
submarines www.vlf.
it
radio
communications,
telegraphy, inductive
heating
radio
radio transmissions,
radio amateurs,
spying
remote controls,
closed networks, tv,
radio amateurs, radio
navigation, military,
police, taxi
Motion Mountain – The Adventure of Physics copyright © Christoph Schiller June 1990–November 2015 free pdf file available at www.motionmountain.net