Frequency,
Hz1022
1021
1020
1019
1018
1017
1016
1015
1014
1013
1012
1011
1010
109
108
107
106
105
104
103(1 GHz)(1 MHz)(1 kHz)Photon
energy, eV107
106
105
104
103
102
10
1
10 –1
10 –2
10 –3
10 –4
10 –5
10 –6
10 –7
10 –8
10 –9
10 –10
10 –11(1 MeV)(1 keV)RadiationWavelength,
m10 –13
10 –12
10 –11
10 –10
10 –9
10 –8
10 –7
10 –6
10 –5
10 –4
10 –3
10 –2
10 –1
1
10
102
103
104
105(1 pm)(1 nm)(1 μm)(1 mm)
(1 cm)(1 km)GammaraysUltra-violetInfraredRadioVisibleTV, FMStandard
broadcastX-raysMicro-wavesFigure 2.2The spectrum of electromagnetic radiation.their frequencies. Light waves, which are em waves the eye responds to, span only a
brief frequency interval, from about 4.3 1014 Hz for red light to about 7.5 1014
Hz for violet light. Figure 2.2shows the em wave spectrum from the low frequencies
used in radio communication to the high frequencies found in x-rays and gamma rays.
A characteristic property of all waves is that they obey the principle of superposition:When two or more waves of the same nature travel past a point at the same time,
the instantaneous amplitude there is the sum of the instantaneous amplitudes of
the individual waves.Instantaneous amplitude refers to the value at a certain place and time of the quan-
tity whose variations constitute the wave. (“Amplitude” without qualification refers to
the maximum value of the wave variable.) Thus the instantaneous amplitude of a wave
in a stretched string is the displacement of the string from its normal position; that of
a water wave is the height of the water surface relative to its normal level; that of a
sound wave is the change in pressure relative to the normal pressure. Since the elec-
tric and magnetic fields in a light wave are related by E cB, its instantaneous amplitude
can be taken as either Eor B. Usually Eis used, since it is the electric fields of light
waves whose interactions with matter give rise to nearly all common optical effects.Particle Properties of Waves 55
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