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Electrical Applications 2 by David W. Tyler

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108 Illumination
CD
M
en
Cü
>
cu
e
g
o
rr
200xl0
8;/
4xl0
14
7.5xl0
14
?
/
3xl0
18
Frequency Hz
Figure 7.2
The speed of
all
electromagnetic radiations such as light and radio
is
3
x
10
8
m/s (approximately).
At frequencies slightly lower than red there is infra-red radiation
which, although invisible, can be detected by the human skin since it
is warming.
At
the other end
of
the spectrum
at
frequencies above
that
of
violet light, there is ultra-violet radiation which also has
an
effect on the human